Proper nutrition is essential to human growth, de- velopment, and well-being. It is in fact impossible to separate health and nutrition. Four of the ten top leading causes of death among American women—
coronary heart disease, certain types of cancer, stroke, and diabetes—have dietary factors associ- ated with them [1]. Furthermore, the prevalence of osteoporosis and extremes in body weight contin- ues to increase and have reached epidemic propor- tions. It is projected that overweight and obesity will soon replace smoking as the leading contribu- tors to morbidity and mortality in the United States [2]. Measures to reduce this disease burden are rel- atively simple and well researched: maintaining a healthy weight; eating a well-balanced, nutritious diet; not smoking; and exercising regularly.
However, survey data from the American Dietetic Association (ADA) reveal that while women seem to recognize the relationship between diet and health, only about one-third of them actually im- plement dietary strategies to reduce their risk of nu- tritionally related progressive chronic disease [3].
It is essential that midwives incorporate the promotion of healthy nutrition into their clinical and preventive health visits as well as their treat- ment plans for diseases that have dietary factors as- sociated with them. This must be done in a clear manner that avoids conflicting messages and that provides clients with specific steps that can realisti- cally be incorporated into their everyday lives. In order to do this, midwives must have an under- standing of basic nutrition principles and of nutri- tional concerns specific to their client population.
Midwives must then be able to translate this knowl- edge into effective educational messages and nutri- tional recommendations and interventions.
6
ety of foods rather than from nutritional supple- ments. This diet must be balanced in a way that pre- vents nutritional deficiencies and excesses. Variety is essential both to guarantee proper intake of all necessary nutrients and in order to benefit from the protective effects of certain dietary components against diseases such as cancer and heart disease, which research suggests are due to combinations of substances in foods and food groups rather than to the effect of a single substance [4]. The sections that follow review intake recommendations for major nutrients, which can be used as a guide in the plan- ning of a balanced diet, and describe in detail the five major nutrient classes.
Recommended Nutrient Intake
The federal government has issued a series of rec- ommendations based on research data to guide health professionals and the American public in the task of designing a diet that provides adequate and well-balanced intake of the nutrients discussed above. These guidelines include Recommended Dietary Allowances (RDAs), U.S. Recommended Daily Allowances (U.S. RDAs), Reference Daily Intakes (RDIs), Daily Reference Values (DRVs), and Daily Values (DVs). This alphabet soup of recom- mendations can be quite difficult for patients to de- cipher and translate into food choices. The midwife should, therefore, have a basic understanding of these terms in order to assist clients in determining with what frequency and in what quantities each nutrient should be consumed.
The Recommended Dietary Allowances (RDAs) are guides for estimating nutritional needs for all people of similar age and gender. They were estab- lished in the 1940s by the first Food and Nutrition Board of the National Academy of Sciences and are updated every four to five years. Less than half of the over 40 necessary nutrients have an established RDA. It should be noted that RDAs are not daily al- lowances. Our bodies store most nutrients for later use, and it is normal that our intake of specific nu- trients will vary from meal to meal and day to day based on the foods consumed. The RDA for a spe- cific nutrient, therefore, should be the average intake over a 3- to 7-day period. It should also be kept in mind that RDAs were designed to apply to groups (initially to American soldiers during World War II) rather than to individuals, and they are therefore meant for meal planning for healthy groups of peo- ple, such as elementary school or college students eating in a school cafeteria. The RDAs are set quite high so as to meet the needs of almost all (97 to 98
percent) of individuals in a group, and thus may be too high for individual needs.
The Food and Drug Administration (FDA) used the RDAs to create the U.S. Recommended Daily Allowances (U.S. RDAs) in 1973. Designed as nu- trient standards for use on nutrition labels on foods and on vitamin and mineral supplements, calcula- tion of the U.S. RDAs were based on the highest 1968 RDA value for each nutrient in the appropri- ate age and gender category. Until the National Labeling Education Act of 1990 was passed, food labeling using U.S. RDAs was voluntary. With pas- sage of that legislation, however, the government increased regulation of food labels and also called for a reexamination of the U.S. RDAs.
Partly due to the need to eliminate the long- standing confusion created by the similarity in the two terms (RDA and U.S. RDA), and also in order to set recommended levels for nutrients not covered by the U.S. RDA, the FDA in 1993 decided both to change the name of the U.S. RDA to Reference Daily Intakes (RDIs) and to create new reference values for nutrients that did not have an RDA.
Daily Reference Values (DRVs) set standard levels for sodium, carbohydrate, fat, and dietary fiber in- take. Initially, the RDIs for all the nutrients except protein remained the same as the U.S. RDA, but since 1993 the values for certain nutrients have been revised and updated.
The RDIs and DRVs are currently used to cal- culate Daily Values (DVs). Starting in 1994, Daily Values must appear on the labels of FDA-regulated products (including vitamin and mineral supple- ments) and are meant to help consumers use the food label information to plan a healthy diet. Using Daily Values, they can determine what percentage of recommended nutrient intake a particular food provides (based, unless otherwise stated, on a diet of 2000 calories). For example, the DV for fat (based on a 2000-calorie diet) is 65 grams. A food item that contains 10 grams of fat, therefore, pro- vides approximately 15 percent Daily Value for fat.
DVs also help set upper or lower limits for descrip- tive terms such as “low fat” that are often used on food labels. It must be noted that DVs are not meant to set levels of nutrients to be consumed every day, but rather to help determine how partic- ular foods fit in to an overall healthy diet.
The Institute of Medicine’s Food and Nutrition Board developed Dietary Reference Intakes (DRIs), a new set of standards that refer collectively to three reference values developed by the Board using the latest available research knowledge on the role of
nutrients in human health: (1) the Estimated Average Requirement (EAR), (2) the Recommended Dietary Allowance (RDA), and (3) the Tolerable Upper Intake Level (UL). The EAR is the intake value that is estimated to meet the requirement de- fined by a specified indicator of adequacy in 50 per- cent of an age- and gender-specific group. At this level of intake, the remaining 50 percent of the specified group would not have its needs met. The RDA is the dietary intake level that is sufficient to meet the nutrient requirements of nearly all individ- uals in the group. The UL is the maximum level of daily nutrient intake that is unlikely to pose risks of adverse health effects to almost all of the individu- als in the group for whom it is designed. An impor- tant characteristic of the DRIs is that they not only aim at determining minimum nutrient intake levels necessary to prevent nutritional deficiencies, but they also strive to set standards to decrease chronic diseases such as osteoporosis and cancer. (See Tables 6-1–6-3.)
The standards outlined above are used by a range of agencies and individuals for a variety of purposes—from meal planning for military forces and determining eligibility for federal programs such as food stamps and WIC, to creating food la- bels and educational materials on nutrition such as the food pyramid, and determining the need for for- tification of food products. Midwives should un- derstand how to appropriately use these standards in clinical practice when conducting nutritional ed- ucation, evaluation, and interventions both for groups of women and for individual patients. It is of foremost importance for the midwife to remem- ber that these standards are guidelines derived from group data and that they were not created to serve as the sole guideline in determining individual daily nutritional needs. Midwives conducting an assess- ment of a woman’s diet must elicit information on the types of foods in her diet; on dietary patterns (which include religious, socioeconomic and cul- tural factors that impact food choice); on lifestyle practices such as drug and tobacco use and exercise or activity level; on anthropometric data such as weight, height, and blood pressure; and on coexist- ing diseases or disease risks. Using this information in conjunction with the standards outlined above and guidelines on ideal body weight (see the section on weight and body fat measurements below), the midwife will be able to assist a woman in adjusting her diet in a manner that avoids caloric and nutri- tional deficiencies and/or excesses and that pro- motes wellness and disease prevention.
Daily Values TABLE 6-1
Daily Values (DVs) are made up of two sets of dietary guidelines:
1. Daily Reference Values (DRVs)—guidelines for in- take of the following nutrients:
• Fat (including saturated fat)*
No more than 30% of total daily calories; saturated fat should comprise no more than 10% of daily calories**
• Cholesterol
No more than 300 mg per day
• Carbohydrates* 60% of daily calories
• Protein*
10% of daily calories (for adults and children over the age of 4)
• Fiber*
11.5 g per 1000 daily calories
• Sodium
No more than 2400 mg per day
• Potassium
No more than 3500 mg per day
2. Recommended Daily Intakes (RDIs)—guidelines for intake of certain essential vitamins and minerals (in- dependent of total caloric intake):
• Vitamin A:5000 International Units (IU)
• Vitamin C:60 mg
• Thiamin (vitamin B1):1.5 mg
• Riboflavin (vitamin B2):1.7 mg
• Niacin (vitamin B3):20 mg
• Calcium:1000 mg (1.0 g)
• Iron:18 mg
• Vitamin D
• Vitamin E:30 IU
• Vitamin B6:2.0 mg
• Folic acid:0.4 mg (400 mcg)
• Vitamin B12:6 mcg
• Phosphorus:1000 mg (1.0 g)
• Iodine:150 mcg
• Magnesium:400 mg
• Zinc:15 mg
• Copper:2 mg
• Biotin:0.3 mg (300 mcg)
• Pantothenic acid:10 mg
*These DRVs depend upon total caloric intake. Please refer to Table 6-2 on calculating DRVs based on caloric intake.
**The National Cholesterol Program of the National Institutes of Health (NIH) now considers 7% to be the cutoff for the maxi- mum number of calories that should come from saturated fat.
Source:Institute of Medicine Food and Nutrition Board.
Protein
Protein is the basic component of cells and is needed for cellular growth, replacement, and repair.
Enzymes—the substances responsible for control- ling the processes that keep the human body func- tioning—are composed of protein. Hormones, hemoglobin, and antibodies are also composed par- tially or entirely of protein. Protein is in turn com- posed of organic compounds known as amino acids. The different arrangements of amino acids into proteins determine the particular properties of the protein.
There are approximately 20 amino acids that are necessary for human growth and metabolism.
The body is able to produce the majority of these necessary amino acids. There are, however, approx- imately nine amino acids that must be provided by foods. These are known as the essential amino acids. Foods of animal origin such as meat, fish,
eggs, and dairy products provide all of these essen- tial amino acids and are known as complete pro- teins. Proteins derived from plants such as legumes, nuts, and grains are known as incomplete proteins because they lack certain essential amino acids. It is possible, however, with proper meal planning to combine different plant foods to obtain all the es- sential amino acids from a vegetarian diet.
Proteins cannot be stored in the body and must therefore be consumed daily in order to avoid the body breaking down nonessential tissue such as muscle to supply proteins vital for survival. While protein intake deficiencies are common in the de- veloping world, most Americans consume quanti- ties of protein well in excess of the RDA. The average American woman, for example, consumes approximately 70 grams of protein per day [5], which is much more than the RDA for protein for most nonpregnant, nonlactating women 25 to 51 years of age.
There are two ways to estimate desirable pro- tein intake for healthy, nonpregnant, nonlactating adult women:
1.Approximately 10 percent of total caloric in- take should be from protein (Daily Reference Value).
2.Women should consume 0.8 grams of protein per kilogram of ideal body weight (Recommended Dietary Allowance).
Table 6-4 contains a list of foods rich in complete and incomplete proteins.
Carbohydrates
Carbohydrates, which can be found in grains, veg- etables, fruits, and sugars, are the major dietary source of energy. They are also necessary for the di- gestion of proteins and for certain brain functions.
Sugars are known as the simple carbohydrates, and starches and fiber as the complex carbohydrates (including glycogen, the animal starch that serves as a storage molecule for glucose). Sugars may be sin- gle molecules (monosaccharides) such as glucose, fructose, and galactose or double molecules (disac- charides) such as sucrose, maltose, and lactose.
Glucose, a monosaccharide, is the body’s main en- ergy source. These simple carbohydrates provide a readily available source of energy for the body.
Starches—found in potatoes, whole-grain bread, corn, brown rice, and pasta—and fiber found in grains, vegetables, and fruits are polysaccharides composed of long straight chains or branched chains of monosaccharide units.
Calculating Caloric-Dependent DRVs (Fat, Carbohydrates, Protein, Fiber) TABLE 6-2
To calculate DRVs based on total caloric intake, the fol- lowing conversion factors are used:
• Fat:9 calories per g
• Carbohydrate:4 calories per g
• Protein:4 calories per g
Sample calculation for carbohydrates in a 2000 calorie diet:
Recommended DRV for carbohydrates is 60% of daily caloric intake (from Table 6-1).
2000 calories ¥60% = 1200 calories.
1200 calories ÷ 4 calories per g = 300 g of carbohydrates per day.
Source:Institute of Medicine Food and Nutrition Board.
Dietary Reference Intakes TABLE 6-3
• Estimated Average Requirement (EAR):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.
• Recommended Dietary Allowance (RDA):Dietary in- take level that is sufficient to meet the nutrient re- quirements of nearly all individuals in the group.
• Tolerable Upper Intake Level (UL):Maximum level of daily nutrient intake that is unlikely to pose risks of adverse health effects to almost all of the individu- als in the group for whom it is designed.
Source:Institute of Medicine Food and Nutrition Board.
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 glu- cose whenever there is a need for reserve energy.
Dietary fibers are polysaccharides that are dif- ferent from starches in that they are joined by chemical links that cannot be digested by the en- zymes in the small intestine. These fibers are either soluble or insoluble fibers. Soluble fibers are di- gested by bacteria in the large intestine, while insol- uble fibers are not. The typical American diet is characterized by being low in dietary fiber. Fiber in- take among adults in the United States averages about 15 grams. That is about half the recom- mended amount [6]. Research has revealed that di- etary fiber is associated with a decreased risk of heart disease (probably through lowering total cho-
lesterol and LDL levels), diabetes, diverticulitis, and constipation [7, 8]. Although earlier research seemed to suggest that increased fiber intake was protective against colon cancer, more recent data, including evidence from the Nurses’ Health Study, indicate that fiber intake is unrelated to colon can- cer [9]. The Nurses’ Health Study did, however, confirm earlier findings on the role of dietary fiber in reducing the risk of diabetes, heart disease, and diverticular diseases of the colon, thus underscoring the importance of a diet rich in fiber [10].
It is recommended that carbohydrates make up at least 55 to 60 percent of daily caloric intake.
Individuals should try to maximize intake of non- starchy, nonrefined complex carbohydrates, espe- cially fiber, and to minimize intake of the simple sugars and certain starchy foods such as white rice and white potatoes. Simple sugar intake should be 10 to 15 percent of total caloric intake. A desirable intake of fiber is a minimum of 20 to 35 grams per day or 11.5 grams per 1000 calories.
Fats
Fats are also a source of energy and provide more calories per gram than do protein or carbohydrates.
Fats are composed of fatty acids and have various roles in the human body. They are involved in the transport and digestion of the fat-soluble vitamins and are part of cell structure. Stored body fat helps in temperature regulation by serving as insulation and helps to protect vital organs by providing a cushioning effect. Excessive dietary fat intake—in particular, high intake of saturated fat—is related to increased rates of chronic disease and increased morbidity and mortality from these diseases.
There are four types of fats in food which dif- fer from each other in the chemical structure of their fatty acids:
1.Cholesterol 2.Saturated fat
3.Monounsaturated fat 4.Polyunsaturated fat
Cholesterol, a fatlike substance, is present in all animal tissue. There are two types of cholesterol:
(1) dietary cholesterol, which is found in foods of animal origin such as meat and eggs, and (2) blood cholesterol, which is a waxy, fatlike substance man- ufactured by the body and stored in the liver. The body uses blood cholesterol to make estrogen, progesterone, and bile. Cholesterol is also an im- portant component of cell membranes. High levels Food Sources of Protein
TABLE 6-4
Amount of
Food Quantity Protein (grams)
Complete Proteins
Lentils 1 cup (cooked) 30
Beef, chuck, roasted 3 oz 28
Pork, center loin 3 oz 27
Turkey 3 oz 27
Chicken breast 3 oz 26
Flounder 3 oz 25
Tuna, canned 3 oz 24
Beef, lean ground 3 oz 22
Scallops 3 oz 16
Cottage cheese 1/2 cup 15
Ham 3 oz 15
Eggs 2 large 12
Shrimp 3 oz 11
Yogurt 1 cup 8
Milk, any type 8 oz 8
Cheddar cheese 1 oz 7
Incomplete Proteins
Tofu 1/2 cup 10
Green peas 1 cup 9
Peanut butter 2 tbsp 8
Egg noodles 1 cup 7
Brown rice 1 cup 5
White rice 1 cup 4
Bread, whole wheat 1 slice 3
Source:Varney, H., Kriebs, J. M., and Gegor, C. L. Varney’s Pocket Midwife. Sudbury, MA: Jones and Bartlett Publishers, 1998.
of cholesterol in the blood, however, promote the production of fatty plaques in arterial walls causing them to lose elasticity and narrow—a disease process known as arteriosclerosis.
Cholesterol cannot be dissolved in the blood and must therefore be carried by fatty proteins called lipoproteins. The main type of this carrier lipoprotein is known as low-density lipoprotein (LDL). An excess of circulating LDL forms fatty plaques in the arteries. Blood LDL-cholesterol level is, therefore, used as a predictor of heart attacks.
The type of fats and oils that we consume is an im- portant determinant of LDL levels. Research evi- dence suggests that high intake of saturated fat is associated with a rise in LDL levels and therefore in the risk for coronary heart disease and heart attacks [11, 12].
High-density lipoprotein (HDL) is another type of carrier molecule of cholesterol in the body. HDL carries excess cholesterol away from the arteries and back to the liver and is thus known as the “good”
cholesterol. A high level of HDL appears to have a protective effect against coronary heart disease and heart attacks [13]. In women, unlike in men, it ap- pears that HDL levels may be more predictive of the risk for cardiovascular disease than total cholesterol levels [14]. Exercise is strongly associated with higher levels of HDL in the body and, therefore, of lower risk of cardiovascular disease [15].
The National Institutes of Health (NIH) and the American Heart Foundation recommend that the daily dietary intake of cholesterol should be below 300 milligrams. It is also recommended that total serum cholesterol should be below 200 mil- ligrams per deciliter of blood and that HDL level should be higher than 35 milligrams per 1000 mil- liliters of blood.
Another way in which fats are transported through the blood to tissues is in the form of triglycerides. The body also uses triglycerides as a means of storing fat. It is still unclear whether a high triglyceride level is an independent cause of heart disease because many individuals with high triglyceride levels also have high LDL cholesterol and low HDL cholesterol, which are known risk factors for heart disease [16]. It does appear, how- ever, that high triglyceride levels are more predictive of cardiovascular disease risk in women than in men [15]. It is recommended that the level of triglycerides in the blood be below 200 milligrams per deciliter of blood although there are no current recommendations for routine screening of triglyc- eride levels.
Saturated fats come from both animal and plant sources. They are often solid at room temper- ature and are known to raise the amount of choles- terol in the bloodstream. In fact, research evidence indicates that serum cholesterol level is affected more by intake of dietary fat than by intake of di- etary cholesterol. Saturated fats are found in meat fat, butter, whole milk products, coconut oil, palm oil, and palm kernel oil. Of the saturated fats, transfatty acids seem to have the most detrimental effect on blood cholesterol levels [17]. Transfatty acids are formed when food manufacturers partially hydrogenate (saturate) liquid oils in an effort to make the oils stay fresh longer. These acids are most commonly found in deep-fried foods, doughnuts, cookies, pies, shortening, and margarine. The American Heart Association recommends that less than 10 percent of daily caloric intake should be from saturated fats.
Polyunsaturated fats are found mainly in veg- etable oils such as safflower, sunflower, corn, soy- bean, flaxseed, and canola oils in the form of omega-6 fatty acids. They are also the main fats found in seafood in the form of omega-3 fatty acids.
Research has shown that eating polyunsaturated fats instead of saturated fats decreases the level of LDL cholesterol in the blood and is therefore pro- tective against heart disease [11].
Monounsaturated fats are also found mainly in vegetable oils such as olive, canola, and peanut oils.
Like polyunsaturated fats, research indicates that consumption of monounsaturated fats may also de- crease LDL cholesterol when used in the place of saturated fats [11].
In summary, the most recent research on fat suggests that the type of fat consumed is as impor- tant if not more important than the quantity of fat intake. As was outlined above, research evidence suggests that replacing saturated and trans unsatu- rated fats with unhydrogenated monosaturated and polyunsaturated fats is more effective in preventing coronary heart disease than simply reducing total fat intake. It is also important to note that even though a woman’s total cholesterol level may not be elevated, her lipid profile may still indicate that she is at high risk for cardiovascular disease. Women with normal or high LDL levels, low HDL levels, and high triglyceride levels seem to be particularly at risk [16].
Tables 6-5 and 6-6 contain summaries of recommended fat and cholesterol intake and rec- ommended blood levels for cholesterol and tri- glycerides.