Nutrition
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Nutrition and Health
Nutrition
Mary K. Barger
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Health and nutrition are intimately interrelated. Proper nutrition is essential to human growth, development, and well-being. Increasing attention to the role of the body's microbiome, especially in the gastrointestinal tract, in metabolic, cellular, and neurologic functioning has, in turn, increased our knowledge about the direct connection between what we eat and our health. Our dietary patterns and food preferences begin in yoo-tuh-roh from the pregnant person's diet flavoring the amniotic fluid, and they continue after birth based on family tradition and culture, geographic residence, financial resources, and educational levels.
Since the average individual in the United States can expect to live for at least 75 years, they should be aware of the growing body of evidence that suggests a healthy diet can prevent several detrimental conditions, such as cardiovascular disease (including myocardial infarction and stroke), cancer, adult-onset diabetes, osteoporosis, and age-related vision loss. Measures to reduce this disease burden are relatively simple and well researched: maintaining a healthy weight; eating a well-balanced, nutrient-dense diet; not smoking; and exercising regularly. Although Americans have increased their physical activity in the last 10 years and decreased their alcohol and tobacco consumption, not much progress has been made on improving the quality of their diet. Indeed, their Healthy Eating Index (H.E.I) scores remain low, averaging 59 points out of 100 over the last 10 years. Additionally, the rate of obesity in the United States continues to increase, with 11.5% of women and 6.9% of men in the United States experiencing severe obesity, defined as a body mass index (B.M.I) of 40 or greater.
The role of social determinants of health in determining nutritional consumption, dietary patterns, and their consequences cannot be overlooked by the midwife. A person's experience of the food environment is determined by the combination of food availability, perceived affordability, and acceptability. It is not surprising that fruit and vegetable consumption varies by income level and that often-cited barriers to higher consumption include cost, accessibility, and availability. Food availability depends on transportation systems and refrigeration to move a variety of foods, particularly perishable fruits and vegetables, to grocery stores. Food availability also depends on the geographic location of grocery stores and farmers markets, and the ability to access these food sources via public transit systems or other means.
Many locations in the United States are considered “food deserts.” (See the U.S. Department of Agriculture (U.S.D.A) maps in the Resources list at the end of this chapter.) Perceived affordability of food depends on a combination of absolute and relative judgments. Absolute judgments include not only the actual cost but the potential waste due to package size, limited longevity of fresh foods, and satiability of the food. Relative judgments include price compared to another food—often a less healthy alternative—or to prepared fast food. Food acceptability is shaped by taste, texture, smell, convenience, and familiarity. Some of these food environment-related factors can be lessened with education and nutritional counseling or innovative clinical practice such as produce prescriptions, but many require policy strategies at the local and national levels to overcome the barriers to healthy eating.
If midwives are to promote healthy eating habits to their patients, they need to understand some basic principles of nutrition, appreciate the physiologic response of the body to ingested food, and be familiar with current recommendations and the numerous ways these guidelines are measured and communicated to the public. Healthy nutritional intake is essential in all phases of life, including preconception and during pregnancy, and the key principles remain the same for everyone whether they want to lose weight, gain weight, or maintain their current weight. Although understanding individual components of the diet is important for health professionals, counseling people about diet should be positively focused on types of preferred foods and the need to eat a variety of nutrient-dense foods, rather than emphasizing individual macronutrients and micronutrients. Increasingly, midwives are caring for transgender and nonbinary individuals, and more research is needed to develop evidence-based guidelines to support the unique nutritional needs of this population.
Principles of Nutrition and Nutrient Recommendations
Nutrients are the chemical components of food. Humans require more than 40 different nutrients for good health. These nutrients are classified as either macronutrients (fats, carbohydrates, and protein) or micronutrients (vitamins and minerals). Water is also a necessary nutrient, but it does not fit into either category. Water, vitamins, and minerals provide no calories but are necessary, although not totally sufficient, for the body to be able to utilize the energy provided by fat, carbohydrates, and protein.
Vitamin and mineral supplements have become increasingly popular in recent years, and some people incorrectly think these agents can supply all needed nutrients. Ideally, people should obtain both macronutrients and micronutrients from a diet composed of a variety of nutrient-dense foods rather than from nutritional supplements. This diet must be balanced in a way that prevents nutritional deficiencies and excesses.
Variety is essential both to guarantee proper intake of all necessary nutrients and to benefit from the protective effects of certain dietary components against diseases such as cancer and heart disease. Today's research suggests that decreased health risks associated with a healthy diet are due to combinations of substances in foods and food groups rather than to the effect of any single substance or nutrient.
Nomenclature for Nutritional Standards
The U.S. Dietary Guidelines for Americans are updated regularly, with the ninth edition (the most recent version) being published in 2020. The Dietary Guidelines emphasize healthy dietary patterns that people should follow, rather than concentrating on the individual nutrient levels they should consume. Nevertheless, labeling on packaged foods regarding the overall nutritive value of a product can still be useful. Therefore, it is important to be familiar with the nomenclature used by various U.S. governmental organizations for nutritional standards setting.
U.S. nutritional standards have two origins: the Food and Nutrition Board, which is part of the Health and Medicine Division (H.M.D) of the National Academy of Medicine (formerly the Institute of Medicine (I.O.M)), and the Food and Drug Administration (F.D.A). The Food and Nutrition Board standards were originally developed during World War 2 as part of an effort to ensure adequate nutrition for members of the armed services. Since then, these standards have been used to set government policy related to food programs such as the School Lunch Program and food relief efforts globally. The F.D.A guidelines are more recent and are intended to assist consumers in obtaining recommended nutrients in their diets.
Table 6 to 1 compares the terms used by the H.M.D's Food and Nutrition Board and by the F.D.A. An important characteristic of the Daily Reference Intakes (D.R.I's) is that they not only aim to determine minimum nutrient intake levels necessary to prevent nutritional deficiencies, but also strive to set standards to decrease the incidence of chronic diseases such as osteoporosis and cancer.
Most food labels are based on a “typical” diet of 2000 calories per day. However, the number of calories actually needed in a day depends on the individual's daily expenditure of calories. Several formulas are available to calculate how many calories an individual needs daily, but clinicians may not have the time to make those calculations. Another option is to use a website that calculates the number of calories needed to maintain or lose weight when provided with the individual's specific sex, age, height, weight, and daily activity levels (see the Resources section at the end of this chapter).
In general, women of average stature and weight will need between 1600 to 2000 calories per day to maintain their current weight depending on their activity level. Those with obesity or who are very active will
Table 6 to 1 U. S. Nutritional Standards
Food and Nutrition Board, Health and Medicine Division, National Academy of Medicine
Dietary Reference Intakes (D.R.I's)
- D.R.I's aim to determine the minimum nutrient intake levels necessary to prevent nutritional deficiencies, and set standards to decrease chronic diseases such as osteoporosis and cancer. This term has more or less supplanted Recommended Daily Allowance (R.D.A).
- D.R.I's are a combination of the R.D.A and Adequate Intake (A.I).
- D.R.I's also specify the Tolerable Upper Limit (U.L), R.D.A's, estimated average requirement (e.a.r), and Als.
Tolerable U.L
- The maximum level of daily nutrient intake that is unlikely to pose risks of adverse health effects to almost all of the individuals in the group for whom it is designed.
R.D.A's
• Developed and updated periodically.
- Set the recommended average intake over a 3-to 7-day period for each nutrient specified.
- Fewer than half of the more than 40 necessary nutrients have an established R.D.A.
• R.D.A's are set quite high to meet the needs of almost all (97 to 98%) individuals in a group, so they may be too high for individual needs.
e.a.r
- The intake value that is estimated to meet the requirement defined by a specified indicator of adequacy in 50% of an age-and gender-specific group. At this level of intake, the remaining 50% of the specified group would not have their needs met.
Als
- Used to develop a recommended intake when a scientific basis for establishing the e.a.r is lacking.
Food and Drug Administration Daily Value (D.V)
- D.V's appear on F.D.A-regulated products.
- D.V's are not meant to set levels of nutrients to be consumed every day, but rather to help determine how particular foods fit into an overall healthy diet.
- D.V's are calculated based on a diet of 2000 calories per day (unless otherwise stated).
- D.V's are calculated from two sources—D.R.V's and R.D.I.
Daily Reference Value (D.R.V)
• Recommended proportions of protein, carbohydrate, and fat in the diet.
• Recommended grams per 1000 calories of dietary fiber intake.
• Recommended daily maximums for sodium and potassium.
Reference Daily Intake (R.D.I)
• Refers to vitamins and minerals as well as protein for younger children and pregnant and lactating persons per day. To ensure that the nutritional needs of all age groups are met, the R.D.I is calculated from the highest D.R.I for each nutrient.
Abbreviations: Als, adequate intakes, D.R.I, dietary reference intake; D.R.V, Daily Reference Value; D.V's, Daily Values; e.a.r, estimated average requirement; F.D.A, U.S. Food and Drug Administration; R.D.A's, Recommended Dietary Allowances; R.D.I, Reference Daily Intake; U.L, upper intake level. need more calories to maintain their current weight, whereas those who are older, or who are trying to lose weight, will require fewer calories. However, all food is not the same, so calories are simply one consideration within the full scope of an individual's diet. The sections that follow review macronutrients, micronutrients, and the physiologic response to ingested food.
Macronutrients
Macronutrients contain calories and are the energy-providing nutrients for the human body. The three basic macronutrients are fat, carbohydrates, and proteins. Macronutrients are needed in large quantities and meet the bulk of the human body's energy needs. One of the primary components of a healthy diet is consuming fat, carbohydrate, and protein in balanced proportions.
Fats
Fats are an important source of energy, providing more calories per gram than either protein or carbohydrates. Fat provides energy at a rate of 9 kilocalories/g, compared to 4 kilocalories/g for protein and carbohydrates. Fats are composed of fatty acids and have various roles in the human body, including transport and digestion of the fat-soluble vitamins and components of cell structure. Stored body fat facilitates temperature regulation by serving as insulation, and it helps to protect vital organs by providing a cushioning effect. In addition, dietary fat intake increases the pleasure of eating and helps signal satiety during a meal.
Although in the last half of the twentieth century the American Heart Association (A.H.A) led a campaign to decrease intake of fats, particularly saturated fats, due to their purported association with heart disease, evidence to date has not substantially supported a causal link between chronic disease and the consumption of most fats. The A.H.A campaign succeeded in decreasing Americans' fat intake from 45% of total calories to 33.16. However, the percentage of calories consumed from fats is not linked to chronic diseases; instead, what matters is the type and source of fats consumed. Therefore, the focus of nutrition recommendations has shifted to dietary patterns and instead of individual macronutrients.
Body Fats
Body fats need to be distinguished from dietary fat. For example, the cholesterol (a fatlike substance present in all animal tissues) consumed as part of the diet is different than the cholesterol in blood that is measured as part of a lipid panel. Dietary cholesterol is found in foods of animal origin such as meat and eggs, while blood cholesterol is a waxy, fatlike substance manufactured by the body and stored in the liver.
Fifty years of evidence has shown that although there is a slight association between dietary cholesterol and serum cholesterol, dietary cholesterol has a minimal effect on risk for cardiovascular disease due to the complexities of the metabolic effects of ingested food. However, dietary cholesterol may affect the liver. For example, eggs—a common source of cholesterol—are rich in other nutrients that may counterbalance the cholesterol's detrimental effects on the cardiovascular system. In addition, more harmful physiologic effects can occur when an individual substitutes an egg for breakfast with a high-glycemic food, such as a large muffin, as discussed later in this chapter.
The body uses blood cholesterol to make steroid hormones such as estrogen and progesterone, as described in the Anatomy and Physiology of the Reproductive System chapter. Blood cholesterol is also required for production of vitamin D and bile, as well as being an important component of cell membranes.
Several subtypes of cholesterol are found in the body, with the two primary forms being low-density lipoprotein (L.D.L) and high-density lipoprotein (H.D.L). L.D.L transports cholesterol out of the liver to other parts of the body. Cells attach to these particles and then extract either L.D.L or cholesterol. Excess amounts of L.D.L promote the production of fatty plaques on arterial walls, causing them to lose elasticity and narrow, resulting in arteriosclerosis. If a plaque breaks free, it may cause a cardiac event such as a heart attack or stroke. L.D.L is often characterized as “bad” or “lousy” cholesterol. Conversely, H.D.L carries excess cholesterol away from the arteries and back to the liver; thus, it is known as “good” or “healthy” cholesterol.
A high level of H.D.L appears to have a protective effect against coronary heart disease and heart attacks. Exercise is strongly associated with higher levels of H.D.L in the body and, therefore, with lower risk of cardiovascular disease.
Another way in which fats are transported through the blood to cells is in the form of triglycerides. Serum triglycerides are either derived from consumed fat, especially trans fats, or synthesized de novo by body fat or the liver. The amount of triglycerides synthesized de novo is positively correlated with the individual's consumption of refined carbohydrates. Triglycerides store excess calories in adipose cells and are released when a source of energy is needed, especially by the brain. Whether a high triglyceride level is an independent cause of heart disease remains controversial, because many individuals with high triglyceride levels also have high L.D.L and low H.D.L cholesterol levels, which are known risk factors for heart disease. Data collected for the National Health and Nutrition Examination Survey (nhanes) reveal that serum levels of total cholesterol, L.D.L, and triglycerides declined from the 1990s through 2014 in all population subgroups of women, regardless of lipid-lowering medication use.
Dietary Fats
Dietary fats are characterized by the chemical structure of their fatty acids. They are classified into four types: trans fats, saturated fats, polyunsaturated fats, and monounsaturated fats.
Trans Fats. Trans fats are produced when vegetable oils are heated in the presence of hydrogen gas and a catalyst, resulting in a partially hydrogenated oil. Such oils become a solid when they cool, making them easier to transport; they are more stable and unlikely to spoil, providing a longer shelf life; and they can be reheated without breaking down, so they are ideal for making fried foods. Although trans fats are found in small amounts in beef and dairy fat, they are largely consumed in the form of commercially made products.
Trans fats are harmful because they elevate L.D.L cholesterol levels and lower H.D.L cholesterol levels; they also stimulate production of prostaglandins and other eicosanoids that increase inflammation, platelet aggregation, and vasoconstriction. The combination of these effects results in an increased risk for cardiovascular disease, diabetes, gallstones, weight gain, and ovulatory infertility. In 2015, the F.D.A declared trans fats “unfit for human consumption” and banned them from processed foods in 2018, with a final deadline of 2020 for their removal from these products.
Saturated Fats. Saturated fats are derived from both animal and plant sources. These fats often are solid at room temperature and are found in highest amounts in meat fat, butter, whole-milk products, coconut oil, palm oil, and palm kernel oil. Consumption of these fats worsens individuals' serum lipoprotein profiles.
Unsaturated Fats. In contrast to saturated fats, unsaturated fats have several beneficial roles in the body, including improving serum cholesterol levels, reducing inflammation, and stabilizing heart rhythms. These fats are found primarily in vegetable oils, nuts, and seeds, and are liquid at room temperature.
Unsaturated fats are of two types: monounsaturated and polyunsaturated. Monounsaturated fats are found in high concentrations in olives, peanuts, oils such as canola oil, avocados, nuts such as almonds and pecans, and seeds such as pumpkin and sunflower seeds. Polyunsaturated fats are grouped into two types, distinguished by their chemical bonds: omega-6 (n-6) and omega-3 (n-3) fatty acids.
There are several kinds of n-3s but the most studied are alpha-linolenic acid (A.L.A), eicosapentaenoic acid (E.P.A), and docosahexaenoic acid (D.H.A). Both n-6 and n-3 are considered “essential fatty acids” due to the body's limited ability to produce them, which means they must be obtained from dietary sources. Omega-6 fatty (linoleic) acids are found in safflower, sunflower, corn, soybean, and flaxseed oils, as well as canola oils. The omega-3 fatty acids D.H.A and E.P.A are found in oily fish such as salmon, mackerel, anchovies, and sardines, as well as algae. Plant sources of omega-3 fatty acids, such as chia and flax seeds, walnuts, soybean, and canola oil, are rich in A.L.A.
The amount of n-3 fats in the U.S. diet has decreased significantly since the 1950s, in part due to changes in the food chain. Today most meat comes from grain-fed animals; relatively speaking, grain-fed animals have less n-3 fats in their meat than do grass-fed animals. The consumption of oily fish has also decreased over the same period of time, perhaps due to warnings about heavy metals in fish. Observational studies have shown an association between n-3s and a range of health outcomes, including heart disease mortality, mood disorders, cancer prevention, rheumatoid arthritis improvement, and infant development. Results from clinical trials that used n-3 fats supplements to prevent myocardial infarction and stroke have been somewhat mixed, with some evidence suggesting higher supplements in the range of 4 g/day are required to realize a benefit.
In summary, the total number of calories obtained from fat is unimportant for cardiovascular and general health; rather, it is the type of fats consumed that is important for health outcomes. Trans fats should be eliminated from the diet as much as possible. Replacing saturated fats with monounsaturated and polyunsaturated fats will provide modest improvements in protection against heart disease. Consumers should be cautious about the foods they choose to substitute for trans fats and saturated fats, as some seemingly healthy alternatives are not necessarily healthier substitutes. Nevertheless, a good recommendation is to reduce consumption of red meat and whole-milk dairy products, increase intake of fish to at least two 6-ounce servings per week, and increase consumption of soy products, nonhydrogenated vegetable oils, and nuts. Table 6 to 2 provides the distribution of daily recommended values of macronutrients for women age 19 to 30 years, and Table 6 to 3 shows the recommended D.R.I's for women.
: Table 6-2 summary: Recommended daily macronutrient intake for women aged 19 to 30, showing general alignment between the Food and Drug Administration and the Health and Medicine Division. For fat, the FDA recommends 30 percent of daily calories, while the Health and Medicine Division suggests 20 to 35 percent. Carbohydrates are recommended at 60 percent by the FDA and 45 to 65 percent by the Health and Medicine Division. Protein recommendations are 10 percent from the FDA and 10 to 35 percent from the Health and Medicine Division. Both organizations recommend zero trans fat. For saturated fat and cholesterol, the FDA sets limits of less than 10 percent and less than 300 milligrams respectively, while the Health and Medicine Division advises as little as possible. Dietary fiber recommendations are similar, at 25 grams from the FDA and 28 grams from the Health and Medicine Division.
: Table 6-3 summary: Dietary requirements vary by pregnancy and lactation status, with the highest needs occurring during multiple pregnancies. For multiple pregnancies, carbohydrate requirements peak at 330 grams and protein at 175 grams. In contrast, nonpregnant individuals, whether 14 to 18 years old or adults, require 130 grams of carbohydrates and 46 grams of protein. Requirements for those with singletons and those in lactation are identical for protein at 71 grams, while lactation requires 210 grams of carbohydrates and 29 grams of fiber. Water needs range from 2.3 liters for nonpregnant teens to 3.0 liters for adults, pregnant individuals, and those in lactation.
Based on Food and Nutrition Board. Dietary Reference Intakes (DRIs): Recommended Intakes for Individuals. Washington, DC: National Academy of Sciences; 2004, updated 2011; Food and Drug Administration. Food Labeling: Revision of the Nutrition and Supplement Facts Labels. Federal Register 81(103):33742-33999.
Carbohydrates
, which can be found in grains, vegetables, fruits, and sugars, are the major dietary source of glucose, the body's essential energy for cellular metabolism. All carbohydrates except insoluble fibers are broken down by the body into the basic sugars and absorbed in the bloodstream. Glucose, galactose, and fructose can be used immediately by the body or can be stored in the liver or muscle tissue in the form of glycogen, which is then converted to glucose whenever this reserve energy is needed.
In the past, carbohydrates have been described as simple or complex, with people being encouraged to eat more complex carbohydrates. However, this recommendation does not distinguish between the different physiologic consequences that occur after eating different types of complex carbohydrates. Because the amount of insulin production that is stimulated in response to carbohydrate intake is a key factor in the body's physiologic response, researchers have developed two measures to assess this response: the glycemic index and the glycemic load. In general, ingestion of high-glycemic foods results in a worsened lipoprotein profile, more thrombotic activity, abnormal glucose metabolism, increased inflammation, and more cellular proliferation.
Glycemic Index
The glycemic index is a measure of the blood glucose response during the 2 hours after ingesting 50 grams of a carbohydrate contained in a food, compared to a standard 50 grams of glucose. This index is influenced by the amount of fiber and fat in the consumed food, both of which slow the absorption of the carbohydrate. Highly processed grains such as those found in white bread, white rice, and semolina-flour pasta have a high index. For example, white rice's glycemic index is 89, whereas that for brown rice is 45. Vegetables have a low glycemic index due to their fiber content and low natural sugar content; indeed, in some cases, it is hard to even measure their glycemic index. For example, obtaining 50 grams of carbohydrate from broccoli requires ingesting 16 cups. Fruits, although naturally sweet, if consumed as the whole fruit, have a low glycemic index due to the fruit's fiber; for example, an apple has a glycemic index of about 10. Riper fruits have a higher glycemic index. In general, low-glycemic foods have a glycemic index of 55 or less, whereas those with a glycemic index of 70 or greater are considered high-glycemic foods.
Abbreviation: ND, not determined.
Data from Food and Nutrition Board. Dietary Reference Intakes (DRIs): Recommended Intakes for Individuals. Washington, DC: National Academy of Sciences; 2004, updated 2011; Goodnight W, Newman R. Optimal nutrition for improved twin pregnancy outcome. Obstet Gynecol. 2009;114(5):1121-1134.
Glycemic Load
Compared to the glycemic index, the glycemic load is a better measure of the amount of insulin production stimulated by consumption of specific foods. The glycemic load is calculated by multiplying the glycemic index of the food by the amount of carbohydrate consumed, expressed in grams, and then dividing by 100. A low glycemic load is less than 10 grams per serving and a high glycemic load is greater than 20 grams per serving, with values in between considered intermediate. For example, the glycemic index for one cup of brown rice is 45, but the glycemic load is 20. The same amount of white rice would have a glycemic index of 89 and a glycemic load of 40. This is a typical example, in which unprocessed grain products stimulate the production of less insulin than do processed foods such as white rice. The same is true for whole fruits as compared to consuming only the juice of the fruit. A person would need to consume three or four oranges to ingest the same glycemic load as contained in 8 ounces of orange juice.
Fiber
Fiber is a type of complex carbohydrate composed of nonstarch polysaccharides that cannot be digested by enzymes in the small intestine. Fiber is characterized as either soluble or insoluble based on its solubility in water. Soluble fiber types include pectin found in fruits, beta-glucans found in oats and barley, and gums found in beans and cereals. Insoluble fiber types include cellulose found in leaves, root vegetables (for example, beets and carrots), bran, and whole wheat; hemicellulose found in bran and whole grains; and lignin found in plant stems and leaves.
The typical U.S. diet is relatively low in dietary fiber. Fiber intake among adults in the United States averages approximately 16 grams, or only 60% of the recommended amounts. Research has revealed that dietary fiber is associated with a decreased risk of heart disease, most likely through lowering total cholesterol and L.D.L cholesterol levels, and with decreased risk of type 2 diabetes, diverticulitis, and constipation.
The Health and Medicine Division of the National Academies of Science, Engineering, and Medicine and U.S.D.A recommend that carbohydrates make up 45% to 65% of daily caloric intake. People should attempt to maximize their intake of low-glycemic foods rich in fiber, such as whole grains, vegetables, and fruits, and to minimize their intake of high-glycemic foods, such as sweetened and energy drinks; refined grains such as white bread, white rice, and russet potatoes; and high-sugar snacks. A desirable intake of fiber for women is 20 to 28 grams per day.
Protein
Protein is a basic component of cells and is needed for cellular growth, replacement, and repair. Enzymes—the substances responsible for controlling the processes that keep the human body functioning smoothly—are composed of protein. Hormones, hemoglobin, and antibodies also are composed partly or entirely of protein. Protein, in turn, is composed of organic compounds known as amino acids. The different arrangements of amino acids into proteins determine the particular properties of each protein.
Approximately 20 amino acids exist that are necessary for human growth and metabolism. The body produces the majority of these necessary amino acids. Approximately nine amino acids, however, must be obtained through foods; thus, they are called essential amino acids.
Foods of animal origin, such as meat, poultry, fish, eggs, and dairy products, provide all of these essential amino acids and are known as complete proteins. Proteins derived from plants, such as legumes, nuts, and grains, lack certain essential amino acids and are termed incomplete proteins. Even so, a vegetarian diet can supply all of the essential amino acids as long as a variety of plant-based proteins are eaten throughout the day.
Proteins cannot be stored in the body, so each day they must be consumed to avoid the body breaking down nonessential tissue, such as muscle, to supply proteins vital for survival. Recommended protein intake is 0.8 to 1.0 g/kg, or 10% to 35% of total calories. While protein intake deficiencies are common in the developing world, most persons in the United States consume adequate amounts of protein. The average intake of women in the United States is approximately 70 g/day or 15% to 16% of kilocalories consumed, with adolescents and older women having less than average intakes.
The body does not distinguish between animal and plant sources of amino acids. However, protein food sources usually contain other nutrients, such as saturated fat. Evidence from the Nurses' Health Study suggests that substituting plant-based protein for high-glycemic carbohydrates can decrease the risk for heart disease and type 2 diabetes among women.
Physiologic Response to Food Intake
The quality of human nutrition encompasses not only the type of food that is consumed, but also the physiologic and chemical responses to it. Food is a hormonal stimulant whose effects are more powerful than those of most drugs. Understanding this reality may be the impetus providers need to spend time with patients assessing their diets and helping them to choose better foods. The body's response to food intake depends on the composition of both the macronutrients and the micronutrients ingested. With regard to prevention of inflammation and other processes that promote disease, especially chronic disease, the most important physiologic response to food intake is how much insulin production is stimulated.
Distinguishing high-glycemic meals from low-glycemic meals is important in understanding the body's physiologic response to carbohydrates. A high-glycemic meal creates a rapidly rising and high blood glucose response, which results in a similar insulin production response. Subsequently, the blood glucose level falls more rapidly than the insulin level decreases, which results in high insulin levels, low glucose levels, and suppression of glucagon production. Faced with these conditions, the body responds as if adequate glucose is present—that is, it suppresses the secretion of free fatty acids, thereby blocking the body's access to stored fat for energy.
Low glucose levels also cause poor brain function, which stimulates the appetite, especially for a high-glycemic meal. After several more hours, to maintain a euglycemic state, skeletal muscles become insulin resistant, decreasing their glucose uptake. In turn, free fatty acids and cortisol are secreted to allow access to stored glucose from the liver. In addition, other inflammatory hormones are released, causing oxidative stress and potentially damage from the production of excessive free radicals. Over time, this cycle of increased levels of glucose, insulin, and free fatty acids damages pancreatic beta cells, potentially resulting in type 2 diabetes, as well as affecting other processes associated with a variety of conditions, including cardiovascular disease, cancer, neural tube defects in the fetus (if the individual is pregnant), and gallbladder disease.
Eating a diet rich in carbohydrates from whole grains, beans, fruits, and vegetables results in a much more modulated glucose response, in which insulin levels follow but never exceed glucose levels. Therefore, insulin levels are maintained within a narrower range. As glucose levels slowly decline and do not overshoot insulin levels, there is also appropriate glucagon stimulation, which permits access to stored fat as an alternative energy source until the next meal.
Micronutrients: Vitamins and Minerals
Micronutrients are dietary elements that the body needs in trace amounts. Metabolism and use of macronutrients by the body require a host of enzymatic and hormonal processes that are also influenced by the necessary presence of micronutrients—specifically, vitamins and minerals, which for the most part cannot be synthesized by the body. Micronutrient deficiencies can have profound adverse health effects. Such deficiencies are a common health problem in developing nations and in some geographic areas in developed nations.
Vitamins are organic substances used by the body as catalysts for intracellular metabolic reactions, whereas minerals are inorganic substances. Both vitamins and minerals are essential for physiologic function, but must be obtained via the diet. Vitamins are classified as fat-soluble or water-soluble: Water-soluble vitamins are excreted from the body and are not stored, whereas fat-soluble vitamins are stored in body fat.
A few of these micronutrients are highlighted here because they play a special role in women's health, pregnancy, or lactation, or because women in the United States are likely to be deficient in them. The roles of vitamins and minerals in pregnancy are discussed later in this chapter. Table 6 to 3 lists the recommended intakes for selected vitamins and minerals in women ages 14 to 70 years, the requirements in pregnancy and lactation, and common food sources of these nutrients.
Fat-Soluble Vitamins
Large doses of fat-soluble vitamins are stored in the body and can reach toxic levels that have dangerous effects. For example, accumulation of vitamin A, which occurs when this nutrient is ingested as retinol, can result in liver toxicity, visual problems, and increased risk for hip fractures. Vitamin A is important for vision (especially night vision), a healthy immune system, and cell growth. Vitamin A deficiency is rare in the U.S. population, but it may be an important nutrient to attend to in low-resource countries. Table 6 to 4 presents the current recommended daily reference intake of vitamins and micronutrients in women in the United States.
Table 6-4 summary: Recommended daily reference intakes for vitamins and micronutrients in women, where requirements generally increase during pregnancy and lactation. Notable examples include Vitamin C, which rises from 75 milligrams for women aged 19 to 70 to 120 milligrams during lactation, and Folate, which increases from 400 micrograms for nonpregnant women to 600 micrograms during pregnancy. Iron requirements peak during pregnancy at 27 milligrams, compared to 18 milligrams for women aged 19 to 50 and 8 milligrams for those aged 51 to 70. Other significant increases during lactation include Iodine, rising to 290 micrograms, and Choline, rising to 550 milligrams. Phosphorus has a unique trend, with the highest recommendation of 1250 milligrams for nonpregnant women aged 14 to 18, dropping to 700 milligrams for all other groups.
Vitamin D promotes absorption of calcium and phosphate and helps deposit these minerals in teeth and bones, but it also plays a role in health beyond bone formation. Most body tissues have vitamin D receptors; thus, this vitamin is involved with regulation of many systems, such as blood pressure, glucose and insulin regulation, and modulation of the immune system. Vitamin D is a not a true vitamin, as humans synthesize D 3 when their skin is exposed to ultraviolet sunlight.
Vitamin D 3 synthesis from sunlight is affected by the intensity of sunlight, especially related to latitude and season; the presence of air pollution; and factors that limit the skin's absorptive ability, such as the amount of pigmentation, presence of sunscreen, and increasing age. Oily fish and fish liver oils are other sources of vitamin D 3 , although absorption is decreased in people with intestinal malabsorptive conditions. Vitamin D 2 —another form of vitamin D—is derived from plant sterols, such as those found in mushrooms. Vitamin D is also consumed through fortified products, such as dairy and nondairy milks.
Both D 3 and D 2 are inactive forms that require metabolism in the liver to convert the vitamin D to 25(OH)D, the form most commonly used to assess a person's vitamin D levels, followed by metabolism in the kidney to convert it to 1,25(OH)_2D, the physiologic active form.
Vitamin D deficiency has historically been defined as a serum 25(OH) D concentration less than 10 nanograms per milliliter (25 nanomoles per liter), which is the level at which rickets or myopathy develops. Currently, there is some controversy about what constitutes vitamin D deficiency in adults based on whether the goal is bone health only or whether other general health conditions are also considered. H.M.D's Food and Nutrition Board, using bone health as the goal, has defined a vitamin D level of less than 50 nanomoles per liter (20 nanograms per milliliter) as inadequate, with the recommended range for this vitamin being 50 to 100 nanomoles per liter (20 to 40 nanograms per milliliter). This agency recommends supplement intakes of 600 to 800 I.U in the absence of adequate sunlight, with an upper tolerable limit of 4000 I.U. However, the U.S. Endocrine Society, the American Geriatrics Society, and Central Europe guidelines recommend a minimum of 75 nanomoles per liter (30 nanograms per milliliter) as the vitamin D level, with a level in the range of 75 to 155 nanomoles per liter (40 to 60 nanograms per milliliter) considered ideal. These organizations acknowledge that individuals may need to consume 1500 to 2000 I.U daily to achieve these levels, with an upper tolerable level of 10,000 to 40,000 I.U. Adults who have obesity; who take anticonvulsants, glucocorticoids, some antifungals, or antiretroviral drugs; or who have inflammatory bowel disease or gastric bypass surgery may require two to three times this dose to achieve healthy levels.
Despite the current controversy about precisely which serum values represent vitamin D deficiency—vitamin D 25(OH) D levels of less than 20 nanograms per milliliter (50 nanomoles) versus less than 30 nanograms per milliliter (75 nanomoles) —there is no question that vitamin D deficiency is prevalent in all ethnic groups of women in the United States (Table 6 to 5). More than 50% of American women have serum vitamin D levels less than 50 nanomoles per liter (20 nanograms per milliliter), and non-Hispanic Black and Mexican women have particularly low average levels.
:(Table 6-5 summary: ) Median micronutrient levels for women aged 20 to 39 in the U.S. generally meet or exceed adequate levels, with some notable exceptions in Folate and Vitamin D. For Folate, where adequate levels are listed between 95 and 330 nanograms per milliliter, all groups fall below the upper threshold, with the Non-Hispanic Black group having the lowest median at 210. Vitamin D shows significant variation; while Non-Hispanic White women have a median of 66.6 nanomoles per liter, Non-Hispanic Black women are well below the recommended 50 to 75 nanomoles per liter threshold with a median of 32.4. In contrast, indicators like Vitamin B12, Vitamin E, and Iron are adequate across all groups, with Vitamin E showing high median values, such as 1,020 micrograms per deciliter for Non-Hispanic White women against an adequate level of over 500.
Abbreviation: DGLV, dark green leafy vegetables.
$ ^{a} $ Some nutrients do not have Dietary Reference Intake (DRI) but an Adequate Intake (AI) has been established.
$ ^{b} $ Lower values: Food and Nutrition Board; higher values: Hollis and Wagner. $ ^{31} $
Data from Food and Nutrition Board. Dietary Reference Intakes (DRIs): Recommended Intakes for Individuals. Washington, DC: National Academy of Sciences; 2004, updated 2011; Hollis BW, Wagner CL. Substantial vitamin D supplementation is required during the prenatal period to improve birth outcomes. Nutrients. 2022;14(4).
Water-Soluble Vitamins Folic Acid
Among the water-soluble B vitamins, folic acid (vitamin B₉) has a great impact for childbearing people due to its role in preventing neural tube defects. Folate is essential for R.N.A and D.N.A synthesis. Observational studies have shown that high folate levels are associated with lower rates of cancer (especially intestinal cancer), cardiovascular disease, dementia, and depression. Supplementation with folate and other B vitamins has proved effective in lowering homocysteine levels, which are associated with cardiovascular disease.
However, randomized trials involving fairly large populations have not found that vitamin B supplements decrease the incidence of any of these conditions. Nevertheless, folate deficiency is clearly associated with megaloblastic anemia. People at risk for megaloblastic anemia include those with poor diets, those with alcohol use disorder, and those who have malabsorptive disorders or take pharmacologic agents that act as folic acid antagonists (for example, anticonvulsants, sulfasalazine Azulfidine).
Folate is found in liver and leafy greens such as spinach, but the primary dietary sources of this micronutrient in the United States are fortified cereals and flours as well as multivitamin supplements. Folate status can be assessed by either serum folate or red blood cell (R.B.C) folate tests, with the latter being a better indicator of tissue levels or long-term status.
In general, the U.S. population is not folate deficient. Since food fortification began in the mid-1990s, the percentage of the population that is folate deficient, defined as being at risk for hypersegmented R.B.C's, in all age and ethnic groups has been 1% or less. However, approximately 20% of U.S. reproductive-age women have folate levels considered inadequate for protection from neural tube defects. Although there is little risk of toxicity from high folic acid intake, concern has arisen that consumption of excess amounts could exacerbate the anemia and cognitive symptoms associated with vitamin B 12 deficiency. Therefore, folic acid supplements of 1 milligrams or more require a provider prescription.
Abbreviation: RBC, red blood cell.
$ ^{a} $ Amount to prevent hypersegmented RBCs.
$ ^{b} $ Amount to prevent neural tube defects.
Bolded text: Deficient levels using the highest standard (e.g., for pregnancy if applicable).
Data from National Center for Environmental Health. Second National Report on Biochemical Indicators of Diet and Nutrition in the U.S. Population. Atlanta, GA: Centers for Disease Control and Prevention; 2012.
Vitamin B _{12}
Vitamin B 12 deficiency can lead to anemia, as well as neurologic and cognitive dysfunction including depression. Everyone needs vitamin B 12 in their diet; human beings do not make this vitamin on their own, and the vitamin B 12 that may be produced by bacteria in the colon is mostly not bioavailable. Subgroups at risk for vitamin B 12 deficiency are those with small bowel or inflammatory bowel disease, those with a history of gastric bypass surgery, vegans, and elderly persons. If a pregnant person is vitamin B 12 deficient, they should be quickly treated, since this condition may affect the developing fetus.
Beef liver, beef, fatty fish (for example, salmon), and dairy products are good dietary sources of vitamin B 12 . For vegans, this nutrient may be obtained from soy and other products such as nutritional yeast, which is fortified with vitamin B 12 .
Recommended routine supplementation of vitamin B 12 and eating vitamin B 12-fortified foods is recommended by the Food and Nutrition Board for all adults older than age 50 due to the prevalence of atrophic gastritis in older adults, which inhibits absorption of vitamin B 12 . There is no evidence that supplementation in those without neurologic disease or vitamin B 12 deficiency improves cognition, depression, or fatigue.
Vitamin B 12 supplements may be provided as injections, orally, or intranasally. Oral supplements are relatively inexpensive and widely available. Methylcobalamin, adenosinecobalamin, and hydroxycobalamin are natural bioidentical forms of vitamin B 12 found in commercial supplements. However, the most common form in supplements and the best studied is the synthetic compound cyanocobalamin. However, smokers should be aware that cyanocobalamin supplements may not be effective for them due to their higher excretion rates of this compound and should consider a different bioidentical form of the supplement. Polymorphisms may affect the bioavailability of different forms, so individuals may need to try different formulations to improve their serum levels. A typical oral vitamin B 12 supplementation regimen might be 250 to 500 mcg/day, which would probably compensate for poor absorption of the supplements. Few data are available on differences in bioavailability between sublingual and oral doses, but it appears that sublingual doses are equivalent to injections for elderly persons. Intake of relatively high doses of vitamin B 12 does not appear to be associated with any detrimental health problems, so no upper tolerable limit has been established.
In summary, most women in the United States have adequate intakes of vitamins, except for vitamin D and, in some subpopulations, folate or vitamin B 12 (for example, in the elderly subpopulation). Nutrition scientists have been learning more about the roles that vitamins play in health beyond the basic understanding achieved in the twentieth century. Randomized trials on the use of vitamin supplements to prevent chronic disease have yielded disappointing results, but it may be that, without addressing the content of the entire diet, vitamin supplementation is not powerful enough to overcome the physiologic effects of types and amounts of macronutrients in the diet.
Minerals
Minerals are chemical compounds found in the earth and absorbed by plants or animals, or dissolved in water. The five major minerals found in the human body are calcium, magnesium, phosphorus, potassium, and sodium. The other minerals needed in minute quantities, called “trace minerals,” have specific functions within the body; they include cobalt, copper, iodine, iron, manganese, molybdenum, and selenium. The minerals reviewed in this chapter are those commonly associated with deficiencies and their resulting adverse health conditions.
Calcium
Calcium is essential not only for healthy bone and teeth formation, but also for nerve conduction, muscle contraction, and blood clotting; given the last function, it plays a role in cardiovascular health. Additionally, it is an important treatment for hypoparathyroidism. Because approximately 20% of women in the United States older than 50 years are at risk for bone fracture due to osteoporosis, maximizing peak bone mass through adolescence and early adulthood is essential. Unfortunately, adolescent girls have the lowest total intakes of calcium, 918 milligrams ± 30 milligrams per day, with only 13% to 15% meeting the daily requirement of 1300 milligrams from both diet and supplements. In addition to calcium's role in building bone mass during adolescence and early adulthood, it is important that women obtain adequate amounts of calcium throughout the lifespan to maintain bone mass. Among women using supplements who are older than age 40, more than 40% of their calcium intake comes from daily supplements or calcium carbonate antacids. Recent studies have highlighted the potential adverse effects of taking calcium supplement doses of 1000 milligrams or more per day, such as an increase in myocardial infarction events and increased incidence of hip fractures and kidney stones. Some evidence suggests that these adverse effects occur with excessive amounts in the form of supplements, but not dietary sources.
Iodine
Iodine is essential for normal thyroid function, and deficiency of this mineral can lead to an enlargement of the thyroid gland known as goiter; it can also have devastating effects on fetal and infant neurobehavioral development. Iodine deficiency has been associated with decreased ability to conceive. The leading sources of dietary iodine in the United States are dairy foods, eggs, seafood, and seaweed. From the late 1970s through 2010, iodine levels in the U.S. population declined by 50%, though these levels have since stabilized. This decline is probably due to a combination of decreased intake of salt, especially iodized salt, fish, and possibly dairy products, or a decrease in the amount of iodine in cow feed, which collectively account for 60% of iodine intake. The recommended daily intake of iodine is 150 mcg in nonpregnant women and 220 mcg in pregnancy, which would result in the World Health Organization's (W.H.O's) recommended sufficient urinary iodine levels of 100 mcg/L and 150 mcg/L, respectively. The most recent data show that, in general, the U.S. population obtains sufficient iodine, but 40% of childbearing-age women have deficient urinary iodine levels ( less than 100 mcg/L) and all population groups are below the pregnancy recommendation, but especially non-Hispanic Asian women (see Table 6 to 5). However, since 2005, when the American Thyroid Association made the recommendation that prenatal vitamins be formulated to contain 150 mcg of iodine, the nhanes data suggest that mean urinary iodine levels in pregnant people have increased to 144 mcg/L; they may be higher now, given that the latest data are from 2014.
Iron
The most common nutritional deficiency globally is iron deficiency, which disproportionately affects women. Iron is essential to the production of hemoglobin and, therefore, for the transport of oxygen. R.B.C's contain 80% of the body's iron, where it can be measured as hemoglobin. Iron not in R.B.C's is stored as ferritin; transferrin is a protein needed for this stored iron to be transported in the circulation. Women who are not pregnant are at risk of anemia because of iron loss during menstruation, coupled with inadequate iron intake or decreased iron stores associated with close spacing of pregnancies. Special populations of people at higher risk for iron-deficiency anemia include pregnant people and those with malabsorption conditions, such as individuals with inflammatory bowel disease and those who have undergone bariatric surgery. Slightly less than 1 milligrams of iron is lost from the intestines daily; this daily iron loss is more than 1 milligrams among people with Helicobacter pylori infection, malaria, or infection with intestinal parasites.
Two forms of iron are found in food: heme and non-heme. Heme iron found in animal products is absorbed more efficiently than non-heme iron. For example, 20% to 30% of heme iron is absorbed, compared to 2% to 10% of non-heme iron.
Iron uptake also varies according to the specific needs of a person's body. If a person has adequate iron stores, only approximately 10% of ingested iron is absorbed. In the presence of iron deficiency, however, as much as 40% of ingested iron can be absorbed.
Some foods or supplements can enhance or inhibit iron absorption, and these items should be discussed when counseling patients. Iron uptake enhancers include animal muscle from meat, chicken, or seafood; fermented vegetables and sauces (for example, sauerkraut, kimchee, and soy sauce); and, in populations deficient in vitamin A, vitamin A. The current evidence does not support a role of vitamin C in enhancing non-heme iron absorption or absorption of iron supplements. Iron uptake inhibitors include foods containing phytates (for example, whole grains, oats, bran, nuts, spinach), phenols (for example, tea, especially green tea; coffee; cocoa; and red wine), calcium, and soy proteins. Iron absorption also is decreased in the presence of antacids.
Pica—a condition characterized by persistent and compulsive eating of non-nutritive substances, including excessive consumption of ice—can be either a symptom of iron-deficiency anemia or a contributing cause. Frequently, correcting the anemia will eliminate the pica.
The loss of iron stores is followed by anemia. Adequacy of iron stores can be measured in several ways. The most commonly available tests assess characteristics of the R.B.C's, such as hemoglobin level, and a peripheral smear to characterize the morphology of the R.B.C's. However, biochemical tests of serum ferritin and transferrin saturation measure earlier stages of iron depletion prior to actual iron deficiency as evidenced by a low hemoglobin level. The primary laboratory and clinical findings with differing states of anemia are discussed in the Common Conditions in Primary Care and Pregnancy-Related Conditions chapters. Although iron-deficiency anemia typically is associated with pale (hypochromic) and small (microcytic) R.B.C's, changes in R.B.C morphology occur relatively late in the process.
In a large study of a multi-ethnic sample of non-pregnant women age 25 to 44 years in the United States and Canada, the prevalence of iron-deficiency anemia (strictly defined as a ferritin level less than 15 ng/dL and transferrin saturation less than 10%) ranged from nearly 3% for non-Hispanic white women to more than 6% for Native American, Hispanic, and non-Hispanic Black women. The rates of deficiency were significantly higher in pregnancy compared to nonpregnancy in white women (4.4% versus 2.8%) and Native American women (25% versus 6.3%), while non-Hispanic Black women had a lower prevalence of anemia in pregnancy (3.5% versus 6.1%). These rates are considerably lower than those reported for low-income pregnant populations in the United States using Special Supplemental Nutrition Program for Women, Infants, and Children (W.I.C) services, which used hemoglobin to define anemia. In 2018, the overall prevalence of anemia among W.I.C participants was 11.4%, with non-Hispanic Black women having the highest prevalence.
People diagnosed with iron-deficiency anemia who increase their dietary consumption of iron-rich foods and avoid taking antacids 2 hours before or 4 hours after meals may correct the problem nutritionally. The other option for remedying this deficiency is iron supplementation. After the addition of 30 to 100 milligrams of elemental iron taken daily, an increase in the reticulocyte count should be noted within 2 weeks and an increase in the hemoglobin noted within 3 to 4 weeks.
Ferrous salts are the first-line choice for oral iron supplementation for the treatment of iron-deficiency anemia. Other types of iron supplements are not more effective, do not appear to have a more benign side-effect profile, and cost approximately four times as much as ferrous salts. Because only a maximum amount of absorption is possible at one time, divided doses are preferable.
Also, separating administration of iron from ingestion of a multivitamin can maximize absorption. A key safety issue is that iron supplements—particularly those : prescribed prenatally—are a source of childhood poisoning.
Side effects of iron therapy, such as nausea, bloating, abdominal cramping, and constipation, are proportional to the dose. In many cases, people discontinue the therapy due to these side effects. Patients should be counseled about the potential side effects and measures they can take to lessen them.
An alternative to daily iron supplementation is taking 120 milligrams of elemental iron once or twice weekly. It is not recommended that people double their multivitamin supplement in an effort to obtain added iron, as this approach could result in excessive levels of fat-soluble vitamins.
Table 6 to 6 lists types of iron supplements and the amounts of elemental iron in each dose. Enteric-coated and slow-release iron formulations are not recommended because iron is absorbed in the small intestine and these products provide iron that is excreted unabsorbed.
Table 6-6 summary: Iron supplements categorized by form and type. For Iron Salts administered as tablets, Iron sulfate (FeoSol) has a total dose of 325 with 65 for the brand; Iron fumarate (Feostat, Hemocyte) is 200 with 66 for the brand; and Iron gluconate (Fergon) is 240 with 27 for the brand. Liquid Iron Salts include Iron sulfate elixir (FeoSol Elixir) at 220 with 44 or 300 with 60 per 5 mL, and Iron gluconate plus herbs (Floradix or Floravital) at 10 per 10 mL with a higher absorption rate. Polysaccharide Iron or Carbonyl Iron options include tablet forms of Carbonyl iron (FeoSol caplets) at 50 with 45 for the brand, and Polysaccharide iron (Ferrex-150) at 150 with 150 for the brand, as well as Polysaccharide iron elixir (Niferex Elixir) at 100 with 100 per 5 mL.
Role of Vitamin and Mineral Supplementation
Ideally, micronutrients should be obtained through intake of a variety of fruits and vegetables each. day—at a minimum, five servings per day—and exposure to adequate sunlight. Unfortunately, fruit and vegetable intake among Americans remains very low, with the median daily intakes being 1 and 1.6 servings per day, respectively; fewer than one in eight individuals meets the daily fruit recommendation and only 10% meet the recommendation for vegetables.
Use of supplements is not a substitute for a healthy diet. Currently half of U.S. adults take a daily supplement, 33% of whom take a multivitamin/mineral version. For some micronutrients, U.S. adult intake from supplements is much higher than from food (for example, B-vitamin intake is 5 times higher from supplements than from food). In some cases, supplements make up for intake shortfalls (for example, for vitamin D); in other cases, their ingestion may result in excess intake (for example, of calcium and folic acid). Too much of these micronutrients can be harmful to cardiovascular health. The U.S. Preventive Services Task Force (U.S.P.S.T.F) states there is insufficient evidence to recommend routine multivitamin/mineral supplementation for the general population. However, this recommendation does not apply to populations at risk for deficiencies, including persons who have undergone gastric bypass and those who have malabsorptive conditions or take medications that can result in lower absorption. As discussed in the section “Dietary Patterns,” limited supplementation should be at least considered by those consuming a vegetarian or vegan diet.
There is no conclusive evidence to support the use of supplements in generally healthy populations to prevent chronic diseases, such as cardiovascular disease, cancer, and diabetes. A randomized controlled trial among 21,000 older adults followed for 3.6 years showed no effect of multivitamin supplements on cardiovascular outcomes or total cancers. Of note, the U.S.P.T.F has assigned a “D” rating (moderate certainty of harm) to intake of beta-carotene and found no effect for vitamin E supplements in the prevention of cardiovascular disease and cancer. Surprisingly, studies have shown supplements of vitamin D and calcium in older adults do not prevent fractures. There are problems with supplement studies, such as a lack of uniformity of definition, identification of the micronutrients in the multi-supplements, reliance on self-reports for dose data, and length of studies. Additionally, as pointed out in the physiologic section, micronutrients are important for certain enzymatic processes but the quality and type of macronutrients initiate important physiologic responses that probably have a larger effect on long-term health. Rarely do studies examine the macronutrient effect in combination with the supplement. At the very least, multivitamin/mineral supplements do not seem to cause any harm. Therefore, in general, taking a multivitamin/mineral supplement "just in case" seems to do no harm, although it may not be money well spent.
Dietary Patterns
In research studies, the quality of the totality of what participants eat and drink are typically measured one of three ways: the Healthy Eating Index (H.E.I), the Alternative Healthy Eating Index (A.H.E.I), or the Dietary Approaches to Stop Hypertension (dash) score. The H.E.I measures how a set of foods aligns with the latest recommendations; the maximum score is 100. Revised H.E.I scoring for the latest 2020 U.S.D.A recommendations is in progress. The A.H.E.I assigns scores to foods based on their predictive value in preventing chronic disease. dash scores measure adherence with the dash diet out of 70 points. All three indexes demonstrate that populations with high diet scores have lower rates of all-cause mortality, cancer, diabetes, and cardiovascular and neurogenerative disease. Emphasizing the importance of the totality of what we eat is important.
When discussing nutrition, a healthcare provider will probably be of most value to patients by emphasizing healthier dietary patterns that are relevant at any weight and applicable throughout the life course. The word"diet" is often interpreted by many laypersons too narrowly—that is, as meaning"a weight-loss diet." It may be helpful, therefore, to use a less-familiar term such as"dietary pattern" with patients when counseling them on nutrition. The U.S.D.A Dietary Guidelines for Americans 2020 to 2025 highlight three food patterns that are recommended as healthy dietary patterns: (1) the Healthy U.S. style pattern; (2) the Mediterranean-style eating pattern; and (3) the Healthy Vegetarian eating pattern.
A 2020 systematic review identified moderate support for these patterns in the prevention of chronic disease. When making dietary suggestions, it is key to consider the individual's preferences, culture, and budget.
The same graphic, MyPlate, can be applied to all three dietary patterns (see the Health Promotion Across the Lifespan chapter). Essentially half of a food plate should be occupied by whole vegetables and fruits (minimum of five servings per day), one-quarter with whole grains, and one-quarter with protein, with low-fat dairy pictured as the drink. Not part of the MyPlate graphic but part of the more detailed description is limitation
Table 6 to 7 Key Principles in a Healthy Eating Pattern
1. Choose healthy fats instead of unhealthy fats.
Avoid trans fats; choose monounsaturated and polyunsaturated fats.
2. Choose slowly digested carbohydrates over highly refined ones.
Emphasize whole fruits, vegetables, beans, and nuts.
Choose whole grains, such as brown rice, bulgur, barley, quinoa, and wheat berries.
3. Choose proteins that are plant based at least half of the time, and choose fish, eggs, and poultry the rest of the time, eating little red meat.
4. Eat large amounts of fruits and vegetables—a minimum of five servings per day.
5. Choose low-calorie hydration—water is best.
• Drink coffee and tea in moderation.
If milk is part of the diet, choose low-fat types.
Limit juice to one small glass per day.
• Avoid high-sugar drinks.
Limit alcohol intake to one glass per day.
6. Meet daily recommendations for vitamins and minerals.
7. Get daily exercise—30 minutes of brisk walking daily.
Calories expended are important to maintain a healthy weight.
of added sugar, especially in the form of sweetened drinks (which are the leading source of sugar for Americans); saturated fats; and sodium. The A.H.E.I promotes the Healthy Eating Plate, which differs slightly from MyPlate in that the drink illustration replaces dairy with water, fruit is a smaller portion than vegetables, and healthy oil is visually depicted. If a clinician uses the MyPlate graphic in counseling, it is important to discuss what a person drinks during the day because fruit juices and sweetened beverages have a high glycemic index, are high in calories, and not nutritionally dense. General principles for following a Healthy U.S. style or Mediterranean-style eating pattern are summarized in Table 6 to 7.
Variety of Plant-Based Diet Patterns
The number of Americans stating they consume a vegetarian or vegan diet has increased rapidly in recent years, with 10% reporting that they follow one of these diet patterns. Reasons cited for a change to a plant-based diet, besides religious or cultural issues, are concerns for animal welfare, personal health, and the environment. In general, a vegetarian diet does not include meat, poultry, or fish. A vegetarian diet is subclassified as either lacto-ovo-vegetarian, which includes dairy products and eggs, or vegan, which does not contain any animal products. Both types of vegetarian diets can be nutritionally sound throughout the lifespan, including during pregnancy and lactation.
Because vegetarian diets are generally lower in saturated fat and higher in fruits, vegetables, and whole grains, this dietary pattern can reduce the risk of some chronic diseases. Population studies of vegetarians have found a lower incidence of obesity, hypertension, type 2 diabetes, and ischemic heart disease, and lower L.D.L cholesterol levels, compared to nonvegetarian populations. People adhering to a vegetarian-type diet pattern also have lower body fat and a more favorable body fat distribution.
When consuming a vegetarian diet, attention must be paid to some nutrients that are not found in large quantities in vegetarian food sources, such as vitamin B 12 , vitamin D, calcium, and n-3 fatty acids. Essential amino acid needs can be met by eating a wide variety of plant foods during the day.
Vitamin B 12 deficiency is the most common nutrient deficiency in persons who eat a vegetarian diet. Unfortunately, the foods in a typical vegan dietary pattern cannot guarantee uptake of sufficient dietary vitamin B 12 for normal functioning. Thus, vegans should assiduously supplement their vitamin B 12 intake with vitamin B 12-fortified foods and supplements. Such fortified foods can include vitamin B 12-fortified nutritional yeasts, vitamin B 12-fortified breakfast cereals, and vitamin B 12-fortified meat and milk alternatives.
No food available to a vegan contains adequate vitamin D and calcium. Vegans appear to have a 40% increased risk of bone fracture risk and more than twice the risk of hip fracture compared to omnivores, so they need to consciously choose fruit and plant sources of vitamin D and calcium. Sunshine on human skin is a significant “source” of vitamin D, but it may not be available to everyone depending on the geographic location and time of year. Fortunately, the F.D.A increased the amount of vitamin D supplementation in non-dairy milks in 2016, so they are now a good source of this nutrient, as are fortified cereals.
Vegans should consider vitamin D supplementation with vitamin D 3 , the best source of this nutrient. Calcium supplements should also be considered.
Cardiovascular disease appears to be less prevalent among vegetarians, even though vegetarians' n-3 fatty acid concentration is often lower than that of omnivores. People consuming a vegan diet must rely on endogenous A.L.A conversion to E.P.A and D.H.A to achieve adequate n-3 levels. However, most vegans' intake is high in linoleic acid (L.A), which inhibits this conversion. It is recommended that to increase their n-3 fatty acid intake, people consuming vegan and vegetarian diets consider algae supplements; decreasing their intake of high-L.A-content food sources, such as nuts, meat analogs, and high-L.A oils (for example, soybean and safflower); and increase their intake of A.L.A-rich foods such as flaxseed, canola oil, and walnuts and walnut oil.
Gluten-Free Diet
The number of people choosing a gluten-free diet has increased rapidly in the United States in the last few years, with the latest estimates suggesting that approximately 1.7% of people living in the United States adhere to a gluten-free diet, including 1.8 million people with celiac disease and 2.7 million people without celiac disease. For persons with celiac disease, adherence to a gluten-free diet decreases inflammation and symptoms of the disease. Although celiac disease and wheat allergy sensitivity are clearly defined disorders related to gluten intake, the health benefits of gluten avoidance in individuals without these issues is questionable. The evidence does not support that a gluten-free diet decreases weight loss or inflammatory bowel conditions, and a gluten-free diet may increase the risk for cardiovascular disease.
The midwife should be aware of potential dietary concerns related to a gluten-free diet. People consuming gluten-free products are at risk for excessive intake of high-glycemic carbohydrates and saturated fat, and deficiencies of fiber, vitamin C, vitamin B 12 , folic acid, and vitamin D as well as calcium, zinc, and magnesium. However, it should be noted that gluten-free pseudo-cereals, such as quinoa and amaranth, have twice the mineral content (including calcium and iron) of traditional cereals. Therefore, the principle of opting for whole-grain forms of food, instead of processed foods, is an important message to communicate.
Persons with celiac disease are at increased risk for poor pregnancy outcomes and osteoporosis. The pregnancy-related risks include prematurity, fetal growth restriction, small-for-gestational-age newborns, and stillbirth; these risks are lower if the disease is well controlled. Therefore, preconception counseling about a gluten-free diet in these persons has the potential to improve their pregnancy outcomes. Additionally, persons with celiac disease are at risk for low bone density that may or may not normalize with a gluten-free diet.
Nutrition Across the Lifespan
Nutritional needs change significantly over the course of a person's lifetime. The latest Dietary Guidelines for Americans highlight nutritional needs from infancy through older age. This section highlights some key issues for reproductive-age individuals, including those related to pregnancy and lactation; nutrition issues for persons of older ages are discussed in the Menopause chapter.
Nutrition During Adolescence
Adolescence is a period of rapid physical growth and, therefore, high nutritional need. During adolescence, girls gain 40% of their skeletal mass and 50% of their body weight. Inadequate nutrition, especially calcium intake, can compromise their peak bone mass.
Unfortunately, the diet pattern of adolescents tends to be poor, with 65% of adolescents having poor food quality scores. Besides poor intake of fruits, vegetables, and whole grains, adolescents consume more than 30% of their calories from calorie-dense, nutrient-poor drinks. Of perhaps greatest concern is the increased rate of obesity among U.S. children and adolescents. However, a prospective study of a multiethnic sample of youth from grades 10 through 1 year post high school found no association between quality of food intake and baseline weight.
In recent decades, the age of onset of puberty has decreased. Earlier onset of puberty can pose significant self-image and psychosocial problems for young children, who may be seen as more socially and emotionally mature than they really are. The reasons for this trend may include increased exposure to environmental pollutants and chemicals, as well as stress; being born small for gestational age, experiencing fetal growth restriction, and not being fed human milk are also risk factors. Likewise, increased body fat in childhood is a strong risk factor for earlier onset of puberty. For every one-point increase in B.M.I, menstruation occurs 1 month earlier. Stage 2 or greater breast development is no longer uncommon at ages 7 and 8 years; the median age for this stage among U.S. girls varies by race/ethnicity from 8.8 for African Americans to 9.7 for Asian Americans. Beyond body fat and environmental factors, type of food consumed plays a role in the development of puberty. Data from national surveys show that the onset of puberty is delayed approximately 7 months in children who consume large amounts of plant protein, whereas those with a high intake of animal protein enter puberty approximately 7 months earlier. Also, greater intake of isoflavone—a nutrient found in soy products, chickpeas, and lentils—delays breast development by 7 months.
Nutrition, the Menstrual Cycle, and Fertility
Nutrition also affects, and is affected by, the menstrual cycle. Studies suggest that caloric intake varies during the menstrual cycle, peaking once in the follicular phase and once in the luteal phase, and reaching a nadir during menses. These changes are theorized to coincide with cyclical fluxes in a woman's basal metabolic rate that are affected by hormones. Women also appear to increase their intake of carbohydrates and fat during the luteal phase, and their intake of protein and fat in the follicular phase, as compared to the menstrual phase. Persons with premenstrual syndrome have similar intakes as those without this condition, but increase their intakes of non-milk sugars and alcohol in the luteal phase. Women with very low body fat levels become anovulatory. There is an association between vitamin deficiency, particularly deficiencies of calcium and vitamin D, and increased physical symptoms of premenstrual disorder.
According to the Centers for Disease Control and Prevention, in the United States, 2.8 million married women are infertile, and another 9.5 million have impaired fecundity. Risk of ovulatory disorders and an inability to conceive is about 60% lower in those adhering to a Mediterranean-type diet pattern or the Fertility Diet compared to a typical Western-style diet, which is low in fruits and vegetables and high in fat and sugar. The Fertility Diet was derived from the Nurses' Health Study. Similar to the Mediterranean-style diet pattern, the Fertility Diet eliminates trans fats; favors consumption of low-glycemic carbohydrates, including choosing more plant-based proteins; and temporarily trades nonfat or low-fat dairy products for the full-fat versions. These diet patterns also increase the ability to achieve and maintain a pregnancy among those persons using assisted reproductive technologies. It appears that in high levels, glucose is not only a teratogen for the growing fetus but also severely affects a developing oocyte; thus, individuals who follow a diet pattern that features a lower glycemic load and who maintain their insulin levels within a narrow range are more fertile.
Women at the extremes in body weight are more likely to have reduced fertility. Therefore, aiming for a healthy body weight is important for improving fertility. Data from the Nurses' Health Study indicate that for people with high B.M.I's, losing 5% to 10% of body weight may improve ovulation, especially if regular exercise is incorporated into the regimen. Lean women who exercise strenuously should reduce this activity to a moderate level to improve their fertility.
Prenatal Nutrition and Gestational Weight Gain
Individuals who have a healthy diet before becoming pregnant need only subtle changes in their eating pattern to optimize nutrition in pregnancy. Energy requirements increase by approximately 200, 300, and 400 calories per day in the first, second, and third trimesters, respectively —an increase that is equivalent to the addition of one healthy snack per day.
Diet quality both preconception and during pregnancy has lasting effects not only on the fetus but also on the child as they grow into adulthood. Increasing evidence supports the effects of diet during pregnancy on the epigenetics of the fetus, which genes become activated through D.N.A methylation, and placental functioning. These epigenetic changes can have short-term effects on closure of the neural tube and oral cleft anomalies as well as long-term effects on cardiometabolic health and cancer. Adverse epigenetic effects occur in the presence of both over-and under-nutrition, the high glucose levels seen with diabetes in pregnancy, oxidative stress, and the lack of key substrates such as fatty acids (for example, D.H.A). Male fetuses appear more vulnerable to epigenetic changes than female fetuses. Therefore, specific and accurate nutrition counseling during pregnancy is more important now than ever.
Weight Gain
Gestational weight gain (G.W.G) is just one aspect of a pregnant person's nutritional status. Indeed, routine weight measurements during pregnancy are not the standard of care in all developed nations. The United States is one of the few developed nations in which weight gain is routinely tracked over the course of pregnancy.
A relationship exists between both insufficient and excess gestational weight gain and adverse outcomes for both the pregnant person and the fetus. Pregestational weight and subsequent G.W.G affects the offspring's weight gain and adiposity. In turn, birth adiposity affects adult weight and long-term health. Inadequate weight gain is associated with low birth weight, small-for-gestational-age infants, preterm birth, increased perinatal mortality, and long-term increased risk for obesity and diabetes. Conversely, infants of pregnant persons who gain excessive weight or enter pregnancy with obesity are at increased risk of being large for gestational age, hypoglycemia, and birth trauma associated with difficult birth. For pregnant people, excessive G.W.G is associated with cesarean birth, postpartum weight retention, and decreased lactation success. Long-term outcomes associated with excessive G.W.G may can include metabolic syndrome, type 2 diabetes, and cardiovascular disorders.
Guidelines for G.W.G have changed over the years. In 1990, the Institute of Medicine (I.O.M) issued pregnancy weight gain guidelines aimed at ensuring adequate weight gain to prevent low birth weight. At the time, the weight gain recommended by I.O.M was higher than the 12-pound weight gain typically recommended in clinical practice. Since then, obesity and excessive weight gain in pregnancy have become public health concerns in the United States. In 2009, I.O.M revisited its recommendations by considering the evidence accumulated since the early 1990s, with a particular focus on the role of retention of G.W.G in the development of long-term obesity in women, and issued new G.W.G guidelines (Table 6 to 8).
The recommended G.W.G differs based on the individual's pregestational B.M.I. The I.O.M recommendations are for the general population in the United States; subpopulations—such as adolescents, people who smoke, and those with chronic illness—may require individualized weight gain targets.
Persons are provided with information about their B.M.I category and target prenatal weight gain using the I.O.M recommendations at the first prenatal visit. Weight gain is then assessed and nutrition counseling reviewed at subsequent prenatal visits. Charting weight gain on a graph gives both the pregnant person and the prenatal care provider a pictorial representation for easy visualization of the G.W.G. Although a composite weight gain graph is often available in prenatal charts, weight gain graphs that show the mean and range specific for each B.M.I category are available. (See the Resources section at the end of this chapter for weight chart sources.) It is essential that pregnant individuals are provided with useful information to help manage their G.W.G. Besides ascertaining food insecurity, conversation starters can include the questions in Table 6 to 9.
Abbreviation: BMI, body mass index
$ ^{a} $ Calculations assume a mean first trimester weight gain of 2 kg (range: 1–3 kg) for people who are underweight, normal weight, and overweight. The assumed first trimester weight gain for people who are obese is 1.5 kg (range: 0.5–2 kg).
Based on Institute of Medicine. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: Institute of Medicine; 2009.
Table 6-8 summary: Recommended weight gain for a singleton pregnancy varies by the person's prepregnancy body mass index. Those categorized as Underweight with a BMI less than 18.5 are recommended to gain 28 to 40 pounds. For Normal weight individuals with a BMI between 18.5 and 24.9, the recommendation is 25 to 35 pounds. Weight gain recommendations decrease for higher BMIs, with 15 to 25 pounds for those in the Overweight category with a BMI of 25.0 to 29.9, and 11 to 20 pounds for those with Obesity and a BMI of 30 or greater.
Table 6 to 9 Nutrition Conversation Starters Food Insecurity Questions ("Yes" to either one indicates some level of insecurity.)
- Within the past 12 months, we were worried whether our food would run out before we got money to buy more.
- Within the past 12 months, the food we bought just did not last and we did not have money to get more.
Starter Questions
• Tell me about the food you usually eat.
• Are there foods you tend to avoid?
- Do you prepare your own food?
- How many times a week do you eat food that you do not prepare yourself?
- When asked about G.W.G, respond with “How do you feel about your food intake?” Strategize about ways to improve nutrition for maternal and fetal health and appropriate G.W.G.
Abbreviation: GWG, gestational weight gain.
Modified with permission from Marshall NE, Abrams B, Barbour LA, et al. The importance of nutrition in pregnancy and lactation: lifelong consequences. Am J Obstet Gynecol. 2022;226(5):607-632. doi:10.1016/j.ajog.2021.12.035.
Dietary Advice
The recommended Daily Reference Intakes for macronutrients and micronutrients for women during pregnancy are summarized in Tables 6 to 3 and 6 to 4. Diet can play a powerful role in maintaining a healthy pregnancy, and prenatal care is an ideal time to start the conversation about a healthy dietary pattern. This is a life event when people are willing to make lifestyle changes for the health of the fetus.
Frequency of meals also plays a role during pregnancy. A substantial body of research supports the recommendation that pregnant people eat three meals a day and at least two snacks. Some people will want to observe their religion's periods of fasting, even though Catholicism, Judaism, and Islam all customarily exempt a pregnant woman from any obligation to fast. As part of prenatal care, the midwife elicits this information and provides teaching as required.
Table 6 to 10 summarizes dietary recommendations during pregnancy, which are designed to meet the unique nutritional needs of pregnancy while reducing the risk of exposure to infections and teratogens. These recommendations are consistent with the healthy, nutrient-dense dietary patterns discussed previously. However, some popular diet patterns are not recommended in pregnancy, including the Atkins Diet, the Paleo diet, and the Ketogenic diet. These diet patterns substantially restrict some macronutrients, which can be harmful during pregnancy due to the resulting micronutrient deficiencies or induced ketosis. The basic message to pregnant people is “Eat better, not more.”
Vitamin and Mineral Supplementation. Prenatal vitamins are multivitamin supplements formulated to provide the vitamins and minerals needed most by pregnant women. Although prenatal vitamins are one of the hallmarks of prenatal care, the actual value of vitamin and micronutrient supplements for pregnant women is more nuanced and complex. First, a balanced diet generally provides all the nutrients needed for health during pregnancy.
Unfortunately, most pregnant people in the United States do not consume a diet that provides all the vitamins and micronutrients needed during pregnancy. The specific vitamins and micronutrients that have documented adverse effects on fetal development if present in insufficient amounts in the diet are folic acid, vitamin D, iron, iodine, and choline.
Folic Acid. Supplemental folic acid is recommended for all pregnant persons. This supplementation needs to be started in the preconception period since closure of the neural tube occurs by 6 weeks after the last menstrual period. Folic acid supplementation begun preconception and taken through the first trimester lowers the risk of neural tube defects (N.T.D's) by approximately 30% to 70%, with the amount of decrease depending on the study conducted and the amount of folic acid used by study participants. The recommended dose is 400 micrograms per day for persons who do not have an a priori risk for N.T.D's. Those who had a previous pregnancy complicated by an N.T.D, have diabetes, have a B.M.I greater than 30, or are taking antiepileptic medication are advised to take 4 milligrams of folic acid per day starting 1 month prior to conception and through the first 4 months of pregnancy.
Iron. Iron is the single most difficult nutrient to obtain via the diet during pregnancy. Iron intake needs are approximately doubled during pregnancy, but iron absorption is also increased with increasing gestational age. However, unlike folic acid supplementation, routine iron supplementation is controversial. Currently, the U.S.P.S.T.F does not find sufficient evidence to recommend routine iron supplementation in pregnancy, and its updated evidence report from 2020 does not provide any more convincing evidence. Iron supplementation increases plasma hemoglobin levels but does not affect overall maternal and neonatal outcomes unless iron is used specifically to treat anemia during pregnancy. Moreover, iron supplements frequently cause gastrointestinal distress.
There is clear evidence that the change in diet patterns away from consumption of red meat has led to decreased iron consumption in the United States. Although the rate of iron deficiency increases during pregnancy from 7% in the first trimester to nearly 40% in the third trimester, the rate of actual anemia is low. Some pregnant populations are especially at risk for anemia in pregnancy, including individuals with multiple gestation, adolescents, non-Hispanic Black people, and vegetarians. Additionally, pregnant individuals with pica may have iron deficiency.
The absorption of iron in prenatal vitamins can depend on the amount of calcium in the vitamin. For example, more iron may be absorbed from a vitamin with a lower iron content and no calcium than from a vitamin containing both calcium and iron. The absorption of iron in supplements depends on the amount of elemental iron in the formulation, whether it is a quick-release or extended-release formulation, and whether the iron is in the ferric, ferrous, or iron polymaltose complex form. Since iron is absorbed in the small intestine, extended-release formulations make little physiologic sense. Table 6 to 6 identifies the equivalent amounts of elemental iron for different iron preparations.
Because iron absorption increases in pregnancy, some authors have proposed that intermittent iron supplementation may be preferable to daily iron supplementation. Exposure of the intestinal mucosal cells to iron supplements on an intermittent basis may improve iron absorption because these cells might absorb iron better if not exposed to it continuously. Randomized controlled trials of intermittent iron supplementation rather than daily iron supplementation demonstrated equally positive pregnancy outcomes when iron supplements were taken one to three times per week rather than daily.
Iodine. Iodine deficiency in pregnancy is the leading cause of intellectual impairment worldwide, with data showing that even a mild deficiency is associated with attention-deficit disorders. Due to the increased production of thyroid hormone in pregnancy and the 30% to 50% increased urinary excretion of iodine in pregnant individuals, the demand for iodine increases both in pregnancy and during lactation. Most U.S. women are mildly iodine deficient, with only one subpopulation meeting the iodine requirements for pregnancy (see Table 6 to 5). The decreased food intake of iodine in recent years has led the American Thyroid Association to recommend routine iodine supplementation during pregnancy. A review by this chapter author of the 18 most recommended prenatal multivitamins from three different “best” lists on the Internet showed that all included iodine, although the source of iodine may not have been the most reliable form.
Choline. Newer research has focused on the importance of choline in pregnancy due to its role in central nervous system development, cell division, and cellular methylation, and its synergistic effect with D.H.A in delivering nutrients to the fetus. Choline demand is very high in pregnancy, with newborns having serum concentrations 3 to 5 times greater than of the birthing person; human milk has 15 times that of maternal serum. Only 8% of pregnant people in the United States have adequate intake of choline according to the current standard, with those following a vegan diet pattern being most at risk for deficiencies. The previously mentioned review of 18 recommended prenatal vitamin formulations showed that only 44% contained choline.
Vitamin D. Vitamin D not only plays a role in assuring bone homeostasis in the pregnant person and fetus, but also is essential for placental functioning and neural development in the fetus. The vitamin D levels in the pregnant person determine the vitamin D levels in the fetus. Certain populations of U.S. women are generally vitamin D deficient (see Table 6 to 5), which has implications for their pregnancy outcomes. Studies of vitamin D supplementation during pregnancy show that pregnant individuals who receive this therapy have lower incidence of preeclampsia and gestational diabetes, and may be at lower risk of a low-birthweight infant and postpartum hemorrhage. In contrast, the evidence for decreased risk of preterm birth with vitamin D supplementation is conflicting. Vitamin D deficiency has also been associated with infant asthma, slowed infant growth, and infant cognitive issues.
There are no current recommendations for routine screening of all pregnant people for vitamin D deficiency, but providers who care for those at risk, such as people who expose little skin to the sun or people with darker-colored skin living in northern climates, might selectively do so. Studies have supplemented pregnant participants with 2000 to 4000 I.U daily.
Prenatal Multivitamins. Prenatal multivitamins generally contain enough of the vitamins and minerals needed by a pregnant person and, therefore, are a convenient vehicle for delivering those micronutrients. Prenatal multivitamins are specifically recommended for people who are in one of the following categories: nutritionally inadequate diet, multiple gestation, cigarette smoking, substance use or alcohol use disorder, adolescent, vegetarian diet, history of bariatric surgery, eating disorder, or lactase deficiency.
The amounts of specific vitamins and minerals in commercially marketed prenatal vitamins vary greatly. Also, the lack of uniform labeling makes it difficult to compare different products. Prenatal vitamins should contain iodine and choline, since levels of these nutrients are low in the general population.
With the addition of extra calcium and the omega-3 long-chain polyunsaturated fats (D.H.A and E.P.A), however, many prenatal vitamins become difficult to swallow. Some manufacturers provide chewable or liquid formulations, whereas others recommend twice-daily dosing. If calcium, iron, and omega-3 supplementation are needed, midwives might consider recommending separate tablets for each nutrient needed.
Prenatal multivitamins can cause increased gastrointestinal distress and constipation in some people. These symptoms presumably arise secondary to the iron content in the vitamin. For individuals who experience nausea and vomiting, discontinuing iron-containing pills does appear to improve nausea symptoms. When a prenatal vitamin is discontinued, even if temporarily, it should be replaced with a folic acid supplement.
Vitamins are not always beneficial. For example, vitamin A in the form of retinol, when taken in large doses, can be a teratogen. Studies have shown that cranial neural crest anomalies may occur when a pregnant person takes as little as 10,000 I.U of retinol daily. Routine supplementation of vitamin A is unnecessary in the United States, and, if supplementation is used, it should not exceed 5000 I.U of retinol daily. Typical prenatal multivitamins contain at least 800 I.U of vitamin A, usually as beta-carotene, which is not a concern as a teratogen. Pregnant individuals should be cautioned not to double or triple their intake of multivitamins to get additional folic acid or calcium.
Abbreviation: BMI, body mass index.
Based on U.S. Food and Drug Administration. Food safety for pregnant women, their unborn babies, and children under five. https://www.fda.gov/media/83740/download. Published January 2022. Accessed June 20, 2022; Barger MK. Maternal nutrition and perinatal outcomes. J Midwifery Womens Health. 2010;55(6):502-511.
Table 6-10 summary: Nutritional and safety guidelines for pregnancy. To prevent neural tube defects, take folic acid in a multivitamin starting one month before conception and continuing for the first three months. Dietary recommendations include eating three meals and two snacks daily, consuming at least five servings of fruits and vegetables, choosing whole-grain carbohydrates and plant-based proteins, and drinking 8 to 10 glasses of water per day. Fish intake should include two 4-ounce servings of best-choice fish, such as salmon or shrimp, or one serving of good-choice fish, such as tuna, while limiting canned tuna to twice weekly. Caffeine should be limited to 200 milligrams per day, and all alcohol must be avoided. Key micronutrients to ensure include beta-carotene for Vitamin A, Vitamin D from sunlight or 1000 to 4000 IU supplements, B12 for vegans, iodine, iron, calcium, and choline. Avoid high-mercury fish like king mackerel and swordfish, as well as raw or unpasteurized foods, including raw eggs, raw fish, raw sprouts, and soft cheeses unless pasteurized. For food safety, wash all equipment used for raw meat and peel raw produce. Cook meat and eggs to 160 degrees Fahrenheit and seafood to 145 degrees Fahrenheit, and heat deli meats until steaming hot.
Special Nutritional Needs
Plant-Based Diets in Pregnancy
With the increased popularity of plant-based diets, more studies have examined the effects of these diets on pregnancy outcomes. A meta-analysis of 22 studies of various degrees of plant-based dietary patterns showed no differences in infant outcomes, with a subsequent systematic review identifying two studies showing an increase in hypospadias. A cohort study conducted after this meta-analysis indicated that pregnant individuals who were vegans or lacto-ovo vegetarians had 2.5 the odds of a small-for-gestational-age infant but no difference in infant morbidities. Greater adherence to a healthy plant-based diet is also associated with a lower risk of gestational diabetes and decreased excessive G.W.G and possibly preeclampsia.
Individuals who eat plant-based diet can meet all their nutritional needs in pregnancy, although some modifications in their eating pattern may be needed. Those who follow a vegetarian diet during pregnancy may not obtain the recommended daily amounts of protein, vitamins B 12 and D, or iron, calcium, iodine, choline, zinc, and omega-3s. The increased protein demands of pregnancy can be met by increasing consumption of legumes, nuts, and soy protein. Vitamin B 12 intake can be adequate among those vegetarians who consume eggs, dairy products, and fortified foods; if their diet lacks a regular source of vitamin B 12 , however, persons consuming a vegan diet need to be certain that they are receiving vitamin B 12 from either fortified soy and rice beverages, fortified foods, or nutritional yeast supplements. Fermented soy products are not a source of vitamin B 12 . It may be appropriate to screen persons on a vegan diet for vitamin B 12 deficiency.
Iron from plant sources is non-heme iron; thus, it is less easily absorbed and more foods can inhibit its absorption than is the case with heme iron. Nevertheless, iron can be obtained in a vegetarian diet.
Nonanimal sources of zinc include nuts and beans. Just as happens with iron, phytates can bind zinc, thereby preventing absorption of this micronutrient. Another source of zinc is fortified cereals.
If they do not consume any dairy products, pregnant persons may not have adequate vitamin D levels and, in the absence of sufficient sunlight exposure, may need vitamin D supplements. The same is true for choline, which mostly comes from eggs and animal proteins. Intake of iodine, which comes from fish, sea vegetables, and dairy products, will be low if these foods or iodized salt are not part of the diet.
Studies have shown that vegetarian diets, and especially vegan diets, are lower in the omega-3 long-chain polyunsaturated fats, D.H.A, and E.P.A, compared to an omnivorous diet. These fatty acids are essential for development of the fetus's retina and central nervous system. It is generally assumed that they must be obtained from the diet, although the exact amounts needed per day and the adverse effects of deficiencies have not been determined. Persons who eat eggs can increase their D.H.A by consuming D.H.A-fortified eggs from hens fed microalgae; otherwise, consumption of microalgae-derived D.H.A supplements is an alternative method for obtaining enough of these fatty acids.
Pregnant with Medical Conditions
Medical conditions that adversely impact nutrition during pregnancy include eating disorders, a history of bariatric surgery, conditions associated with malabsorption, and a need for medications that affect folic acid metabolism. These conditions result in nutritional deficiencies from diminished ability to absorb or metabolize both macronutrients and micronutrients. People with these conditions are at risk for pregnancy outcomes related to decreased supply of nutrients to the fetus—specifically, small for gestational age, low birth weight, preterm birth, and, in the case of a person who has a recent history of hospitalization for anorexia nervosa, stillbirth. Midwives caring for these persons will want to consult with a nutritionist to individualize their care.
Midwives are increasingly providing care for persons after bariatric surgery. Two types of bariatric surgery procedures are commonly performed: (1) restrictive (laparoscopic gastric banding or Lap-Band) and (2) restrictive/malabsorptive (gastric bypass). Lap-Band slippage and movement can occur during pregnancy and result in severe vomiting. Some sources advocate for deflating the band prior to pregnancy to allow for adequate nutrition, though no national guidelines have been established. Current recommendations advise persons to wait 12 to 18 months after bariatric surgery before starting a pregnancy, so that weight loss is stabilized. However, a meta-analysis showed no differences for those conceiving less than 12 months post surgery except for less G.W.G. Knowing the type of bariatric procedure done and when it was performed allows the midwife to provide appropriate nutritional advice and risk screening.
Notably, people tend to become less adherent in taking their multivitamin supplements with increasing time since their bariatric surgery. G.W.G recommendations are based on pregravid B.M.I even after bariatric surgery. Any type of malabsorptive surgery will reduce food, micronutrient, and medication absorption. Therefore, baseline vitamin and mineral status of the pregnant person post bariatric surgery is evaluated at the first prenatal visit, with supplements recommended as needed. A complete blood count and measurement of vitamin B 12 and D, ferritin, and calcium levels every trimester should also be considered, along with early glucose screening.
The midwife providing prenatal care for someone following bariatric surgery must effectively coordinate care among a network of clinicians, including maternal–fetal medicine physicians, nutritionists, and ultrasonographers. Such team-based care optimizes the pregnant person's chance for a safe and satisfying birth.
Pregnant people who are taking anticonvulsant medications (for example, valproate [Depakote, Depakene], carbamazepine Tegretol) should take 4 milligrams of folic acid per day starting 1 month prior to conception and continue that regimen throughout the pregnancy, as these medications have an antifolate effect.
Multifetal Gestation
There are no national guidelines on the increased nutritional requirements for persons with multiple gestations, but extrapolations have been made from singleton to twin pregnancies. There is a consensus for the need for more calories per day, in the range of 40 to 45 kilocalories/kg daily for someone with a B.M.I between 18.5 and 24.9 or about 2400 calories per day. Additionally, 1 milligrams of folic acid per day is recommended. Although individuals with multifetal gestation have lower vitamin D levels, as do their infants, there is no national consensus on how much vitamin D requirements increase in such cases. It is generally recommended that women with multiple fetuses take two prenatal vitamin supplements beginning in the second trimester to obtain the additional iron, folate, calcium, magnesium, and zinc that are needed. This recommendation is safe as long as the vitamin A in the supplements is not retinol; if it is retinol, then the dose needs to remain less than 10,000 I.U.
Pica
Pica is the term applied to the unusual condition in which an individual purposefully ingests nonfood items. Pica is more common in pregnant people than in those who are not pregnant. The prevalence of pica varies by geographic region and culture, but has been noted to affect as many as 50% of pregnant people in some settings. The most common substances eaten are earth, clay, or dirt; raw starches such as cornstarch; and ice and freezer frost.
The etiology of pica is unknown, although several theories exist. There is a clear association between pica and iron-deficiency anemia. Pica can cause lead poisoning and may be associated with other micronutrient deficiencies. Management consists of diagnosis and treatment of nutritional deficiencies, assessment of hunger or eating disorders, and health education.
Motivational interviewing may assist in behavior change and replacing the nonfood substance with a healthy food.
People with Limited Resources
People with low incomes are at increased risk for dietary deficiencies. As mentioned earlier, assessment for food insecurity is essential before any nutritional education. The Special Supplemental Nutrition Program for Women, Infants, and Children (W.I.C) —an income-based, supplemental food program provided by the U.S.D.A—provides food resources and cultural-based nutrition education for pregnant and lactating people, infants, and children younger than the age of 5. Current W.I.C policy is aimed at promoting consumption of healthier foods and access to farmers markets, and has expanded access to fresh fruits and vegetables and improved dietary intakes among this program's participants. The program is also able to connect participants with other important community resources to help improve their pregnancy outcomes.
W.I.C is not an entitlement program, but rather a grant program that requires reallocation of funding annually. Therefore, changes may occur at any time based on federal and state funding.
Conclusion
Research increasingly confirms that good nutrition is essential during all phases of life, and the basic principles of good nutrition remain remarkably consistent throughout the life course. Albeit with some caveats, good nutrition is good nutrition—for those who are pregnant, or who want to lose weight, gain weight, or maintain their weight. The midwife should understand the basics of nutrition and how dietary patterns affect normal physiology. Nutrition counseling should be gently incorporated into a midwife's regular practice so that each person can understand some basic principles of nutrition, the physiologic response of the body to ingested food.
Resources
and current evidence-based dietary guidelines. Although understanding individual components of the diet is important for health professionals, counseling a person about diet should remain positively focused on the types of preferable foods to eat and the need to eat a variety of nutrient-dense foods, rather than emphasizing individual macronutrients and micronutrients. Of course, a midwife should also be prepared with nutrition information specific to pregnancy, be alert to the possibility of eating disorders and refer clients appropriately in such cases, and be ready with encouragement, information, and possible referral to a registered dietician if a person indicates a desire to achieve a healthier weight.
Table summary: Nutrition guidelines, tools, and resources organized by source. Government bodies including the NIH, CDC, and USDA provide a body mass calculator, the MyPlate guide, and the Food Data Central nutrient database. Academic institutions provide specialized tools, such as the Rate My Plate, REAP, and WAVE assessments from Brown University School of Public Health, the Glycemic index from the University of Sydney, and The Nutrition Source from Harvard University School of Public Health. Free smartphone apps for tracking and cooking include MyPlate Calorie Counter, MyFitness Pal, Yumly Recipes and Cooking Tools, and Calorie Counter by Fat Secret. Additionally, the Journal of Midwifery and Women's Health offers nine Share with Women handouts focusing on topics like vegetarian diets and Vitamin D during pregnancy, available in English and some in Spanish.