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to Menu PageOver the course of evolution, human beings (and their primate predecessors) adapted gradually to a wide range of naturally occurring foods, but the types of food and mix of nutrients (in terms of carbohydrates, fats, and proteins) remained relatively constant. Food supplies were often precarious, and the threat of death from starvation was a constant preoccupation for most of the Earth's inhabitants.
About 12,000 years ago, an agricultural revolution brought profound dietary changes to many human populations. The ability to produce and store foods became widespread, and some foods, such as grains, were preferentially cultivated. These new techniques and the overabundance of some foods they produced presented novel challenges to the human digestive system.
The Industrial Revolution, which began about 200 years ago in Europe and soon spread to North America, introduced more radical changes in the human diet due to advances in food ~production, processing, storage, and distribution. Recent technological innovations, along with increased material well-being, or affluence, and lifestyles that have allowed people more freedom in deciding what and when they wish to eat (amplified by modern marketing techniques), have led to even further major dietary changes in developed countries. Indeed, such innovations as sugared breakfast cereals and a variety of snack items were unheard of before World War II; Hampe and Wittenberg (1964) estimated that 60 percent of the items on supermarket shelves in 1960 came into existence in the 15 years following World War II.
Health Consequences of the Modern Affluent Diet
Because changes in the dietary patterns of the more technologically developed countries, such as the United States, have been so dramatic and rapid, the people consuming these affluent diets have had little time to adapt biologically to the types and quantities of food available to them today. The longer term adverse health effects of the affluent diets prevailing in these countries--characterized by an excess of energy-dense foods rich in animal fat, partially hydrogenated vegetable oils, and refined carbohydrates but lacking in whole grains, ~fruits, and vegetables--have become apparent only in recent decades.
Comparisons of population groups have demonstrated a close and consistent relationship between the adoption of this affluent diet and the emergence of a range of chronic, noninfectious diseases, such as coronary heart disease, cerebrovascular disease, various cancers, diabetes mellitus, gallstones, dental caries (cavities), gastrointestinal disorders, and various bone and joint diseases (World Health Organization, 1990). Some nutrition and health experts believe that the relationship between rapid changes in a population's diet and rapidly changing disease and mortality profiles is reflected in many recently acculturated (i.e., adapted to the dominant culture) groups in the United States who are now eating a diet more akin to that of the northern European and U.S. general populations (see the sidebar on page 214).
For example, increasing rates of diabetes mellitus have been reported in Native American and other populations that suddenly switch from a traditional to a more modern lifestyle (West, 1974). This disease has only recently become a major health problem for Native ~Americans, who now often have rates much higher than those found in either U.S. Caucasian or African-American populations. Indeed, although the overall rate of diabetes in the general U.S. population is between 1 and 3 percent, and 5 to 6 percent for those over age 35, it ranges from 10 to 50 percent among Pima Indians 35 years of age and older (Bennett et al., 1979; Neel, 1976). Furthermore, in Hawaii, the incidence of breast cancer for Caucasians is similar to U.S. mainland rates, but the incidence among Hawaii's Japanese population is more than twice the rate in Japan and approaches the rate for Caucasians (Muir et al., 1987).
The reasons for these abnormally high disease rates in American Indian and other non-Caucasian populations are complex; however, they include obesity related to changes in activity patterns and, probably, the increased consumption of refined carbohydrates and sugar. Also, intake of dietary fiber has decreased dramatically. Excessive caloric consumption in some of these populations also may be a major contributor; one study found that obese American Indians consumed 250 to 1,600 more calories than were recommended for persons of their height, gender, age, and level of activity (Joos, 1984).~In one of the few studies of its kind, a group of Native Hawaiians with multiple risk factors for cardiovascular disease believed to be related to consuming a nontraditional diet were placed on a "pre-Western contact," or traditional, Hawaiian diet to assess its effect on obesity and cardiovascular risk factors. Twenty individuals were placed on a diet low in fat (7 percent), high in complex carbohydrates (78 percent), and moderate in protein (15 percent) for 21 days. The subjects were encouraged to eat as much as they wanted. At the end of the diet modification period, the average weight loss was 7.8 kilograms (approximately 17 lbs.), and the average serum cholesterol dropped by about 14 percent. Blood pressure decreased an average of 11.5 mm Hg systolic and 8.9 mm Hg diastolic (Shintani et al., 1991).
Evolution of Federal Dietary Guidelines
Due to the rapid rise in chronic illness related to diet in recent decades, the focus of nutrition research has shifted from eliminating nutritional deficiency resulting from undernutrition to dealing with chronic diseases caused by nutritional excess, or "overnutrition." Since the ~1950s, researchers have identified a number of types of dietary excess that appear to influence the incidence and course of specific chronic diseases.
Another growing concern among nutrition researchers is the accumulation of evidence indicating that inadequate intakes of some micronutrients over a long time may increase the risk of developing a variety of disease conditions, including coronary heart disease, many cancers, cataracts, and birth defects. Earlier, many of these conditions were not even considered diet-related. Furthermore, many other components of foods, in addition to those traditionally considered nutrients, may be important in achieving optimal health. Unfortunately, the "standard" American diet, while rich in calories, contains processed foods deficient in many important micronutrients and other components of the original unrefined foods.
The Federal Government has been involved in developing nutrition guidelines for the American public since the mid-1800s, when the U.S. Department of Agriculture (USDA) was established. However, such guidelines traditionally had dealt with how to prevent ~nutritional deficiencies, as well as how to promote the consumption of U.S. agricultural products. Only in the past several decades, as the focus of public health policy has shifted from preventing disease caused by nutritional deficiencies to preventing disease caused by overnutrition or nutritional imbalances, have Federal dietary guidelines attempted to address the latter. Today, such guidelines are becoming more difficult to develop and often meet fierce resistance from various lobbying groups when they are disseminated (Nestle, 1993).
Nevertheless, since the early 1970s, USDA and other Federal agencies and advisory groups have periodically released diet and nutrition guidelines dealing with preventing chronic illness related to nutrition. This material typically targets public health policymakers, medical doctors, or the general public. Two of the better known current Federal dietary and nutritional guidelines, from which public health policy is made, are the recommended daily allowances (RDAs) and the Food Guide Pyramid.
RDAs are defined as the average daily amounts of essential nutrients estimated, on the basis of available scientific knowledge, as adequate to meet the physiological needs of practically ~all healthy persons (Monsen, 1990). (See figure 1.) To establish the standards for RDAs, which are updated periodically (most recently with the 10th edition in 1989; see Monsen, 1990), the Food and Nutrition Board of the National Academy of Sciences critically evaluates the literature on human requirements for each nutrient, examines the individual variability of requirements, and tries to estimate the efficiency with which the nutrients are biologically available and used from foods consumed. The RDAs are levels that should be reached as averages in a period of several days, not necessarily daily.
RDAs are not meant to be guidelines for consumers; they were initially designed to serve as standards for planning food supplies for population groups (National Research Council, 1989). However, they are used as a partial basis for the development of other guidelines that are intended for consumers, such as the Food Guide Pyramid, which was released by USDA in 1992 to replace the old "basic four" food groups. The Food Guide Pyramid is designed to give consumers information on how to eat a "balanced" diet that will provide them with the RDAs for essential nutrients while lowering their risks of chronic illness due to nutritional excesses (Journal of the American Dietetic Association, 1992). Sweets, fats, and ~oily foods are at the top of the pyramid, indicating that they should be consumed in small amounts. Dairy products such as milk, yogurt, and cheese, and meats, poultry, fish, dried beans, eggs, and nuts are just below, indicating they should be consumed in moderation. Fruits and vegetables follow; bread, cereal, rice, and pasta are at the bottom of the pyramid, indicating that they should be consumed in rather large amounts in comparison with the foods at the top of the pyramid (see figure 2).
Guidelines such as the Food Guide Pyramid are intended to inform consumers, as well as public health policymakers, about what kinds and amounts of certain foods are best suited for maintaining health and lowering the risks of nutrition-related illnesses. Generally, this approach to affecting health through diet and nutrition interventions involves manipulating the "typical," or mainstream, diet so that foods with less nutritional value are eaten less and foods with more nutritional value are eaten more.
The Federal Government's approach to dietary intervention, which has been formulated over the years by boards composed of nutrition scientists, generally does not recommend ~supplementing this "typical" diet with vitamins or nutritional supplements (National Research Council, 1989). It also does not take a "good food" or "bad food" approach (Herron, 1991) or suggest that certain foods are "off limits" because of their propensity to cause chronic disease (Nestle, 1993).