Toward Healthful Diets
Food and Nutrition Board, National Research Council
National Academy of Sciences, Washington, D.C., 1980
Since its inception in 1941, the Food and Nutrition Board of the National Research Council has striven to encourage sound nutritional practices by the U.S. population. A fundamental element of any national nutrition policy, inherent in the recommendations of the Board, is to ensure the provision of a supply of diverse, safe, and attractive foods that will meet the nutritional requirements of the population at reasonable cost.
The first action of the Board, taken in 1941 on the basis of information from the scientific literature, was to recommend allowances of essential nutrients that would assure adequate nutrition in the U.S. population. These Recommended Dietary Allowances (RDA) were calculated to exceed average nutritional requirements by a “safe margin,” taking into consideration the difference in requirements among individuals in a basically healthy population. The allowances are defined as levels of intake of essential nutrients considered, in the judgment of the Food and Nutrition Board on the basis of available scientific knowledge, to be adequate to meet the known nutritional needs of practically all healthy persons. The RDA have been reevaluated and revised at regular intervals as new scientific information has become available. The ninth edition was published in 1980 (FNB, 1980).
The RDA have been accepted by both governmental and non-governmental agencies as the basis for planning and procuring food supplies for population groups, interpreting food consumption records, establishing standards for food assistance programs, developing nutrition education programs, developing new products by industry, and establishing guidelines for nutritional labeling of foods by the Food and Drug Administration. The General Accounting Office (GAO) has recently concluded that the RDA provide the basis for current national policy in nutrition, and urged the Secretaries of Agriculture and of Health, Education, and Welfare to identify research needs and priorities in clinical nutrition, particularly as they relate to concerns about given “food components, lifestyle factors, and diet and health” (Comptroller General of the U.S., 1978). The Food and Nutrition Board recently addressed this issue in response to a request from the National Institutes of Health (FNB, 1979).
The food guides developed by the U.S. Department of Agriculture (USDA, 1957, 1979) have been used in nutrition education to assist people in planning adequate diets that will meet the RDA set by the Board. The RDA are met by selecting servings of foods in given food groups, rather than by calculating amounts of nutrients. In the recent guide, foods are divided into five main groups on the basis of their similarity in nutrient composition. The five groups are (1) milk and other dairy products; (2) meat, fish, poultry, dry beans, and other high-protein foods; (3) vegetables and fruits; (4) cereals and breads; and (5) fats, oils, sugars, and alcoholic beverages. This guide (USDA, 1979) provides information to help consumers identify components from the different food groups in complex foods, such as pizza. The recently published Canadian food guide (Health and Welfare Canada, 1979) is particularly valuable for this purpose. The key to the guides is the information they provide about the number and sizes of daily servings from among the different food groups that will meet the major requirements of given population groups. On the average, 80-120 percent of the RDA for several selected nutrients for adults can be obtained in a diet consisting of about 1,200 kilocalories of properly selected foods. If a diet meets the requirements for these nutrients, it is unlikely to be deficient in others. The recommended selections provide the foundation for a nutritionally adequate diet. It is a sound guide, particularly for sedentary people who have low energy needs and for overweight persons on weight-reducing diets. Active individuals, who have higher nutrient and energy requirements, can meet their needs with additional or larger servings from among the first four groups and may include additional foods from the fifth group, which consists of calorie-rich foods.
The Food and Nutrition Board is concerned about the flood of dietary recommendations currently being made to the American public in the hope that a variety of chronic degenerative diseases my be prevented in some persons. These recommendations, which have come from various agencies in government, voluntary health groups, consumer advocates, and health-food interests, often lack a sound scientific foundation, and some are contradictory to one another. In an effort to reduce the confusion in the mind of the public that has resulted from these many conflicting recommendations, the Board has prepared the following statement.
QUEST FOR GUIDELINES TOWARD HEALTHFUL DIETS
Associations between dietary patterns and disease prevalence have been observed in a variety of epidemiological investigations of coronary heart disease, hypertension, and diabetes. These observations have raised the question whether it is possible to develop additional nutritional guidelines for improving health. In fact, general recommendations to alter consumption of dietary fat, cholesterol, complex carbohydrates, sugar, salt, and fiber have been made to the public by a number of organizations. Such nutritional guidelines for improved health deal not with requirements for essential nutrients but with the pattern of intake of nonessential nutrients or with the intake of essential nutrients in amounts that greatly exceed requirements.
The Board considers it scientifically unsound to make single, all-inclusive recommendations to the public regarding intakes of energy, protein, fat, cholesterol, carbohydrate, fiber, and sodium. Needs for energy and essential nutrients vary with age, sex, physiological state, hereditary factors, physical activity, and the state of health. The nutritional needs of the young growing infant are distinctly different from those of the inactive octogenarian; those of the vigorous active young person differ from those of the sedentary, obese person of middle age. Variations in requirement due to age, sex, physical activity, and individual variability are taken into account in the formulation of the RDA. Guidelines for a healthful diet must also take into account these same variables if they are to be realistic.
The recent Surgeon General’s report on healthy people (DHEW, 1979) has stated that the population of the United States has never been healthier. It reported that age-corrected mortality rates have been falling throughout this century, that life expectancy at birth is continuing to rise, and that the mortality rate for coronary heart disease has declined 20 percent during the last 20 years and is currently falling at a rate of 2 percent per year.
Likewise, death rates from cancers not associated with excessive cigarette smoking have not bean rising, and some have been falling. Nonetheless, heart disease and cancer continue to be the leading causes of death in the United States, together accounting for about 66 percent of total mortality. Both are diseases of multiple etiology. Some argue that because there are associations between dietary practices and the incidence of these diseases, it should be possible to reduce death rates from them by proper nutritional practices.
Although the Board considers it appropriate to set dietary guidelines beyond those implicit in the RDA, in the hope of correcting metabolic patterns in susceptible individuals in such a way as to prevent or delay the onset of chronic degenerative diseases, it is concerned about the adequacy of the scientific undergirding on which these recommendations are based. The Board recognizes that epidemiology establishes coincidence, but not cause and effect. Epidemiologic findings, however, lay the groundwork for further studies to test given hypotheses. Many such studies are in progress. The Board believes that advice should be given to the public when the strength, extent, consistency, coherence, and plausibility of the evidence from lines of investigation ranging from epidemiology to molecular biology converge to indicate that certain dietary practices or other aspects of lifestyle promote health benefits without incurring undue risks.
The American food supply on the whole is nutritious and provides adequate quantities of nutrients to protect essentially all healthy Americans from deficiency diseases. The excellent state of health of the American people as documented in the Surgeon General’s report could not have been achieved unless most people made wise food choices. It is clear, however, that appropriate selections are not made and equitable distribution of nutrients is not currently attained by a portion of the population because of economic, educational, and cultural factors. Inappropriate selection or uneven distribution of nutrients that result in intakes appreciably above or below needs affects nutritional status. The high prevalence in the United States of obesity, which is a form of malnutrition, is due in part to the abundance of appetizing foods. It is not only undesirable physiologically for persons to be too fat, but obesity increases for many persons the risk of developing a number of chronic degenerative diseases.
The Board has considered the current evidence pertaining to relationships between dietary practices and the occurrence of obesity, hypertension. atherosclerosis and its complications (coronary heart disease, stroke. and peripheral vascular disease), cancer. and diabetes. It did not consider dental caries to be a member of this group of chronic degenerative diseases, but endorses fluoridation of water supplies as the most effective preventive measure against this disease (Morgen, 1979).
The ensuing discussion includes specific dietary recommendations that the Board feels are justified at this time.
Obesity, or excess fatness, is the commonest form of malnutrition in the Western nations of the world. It has a multiple etiology and is influenced by neurohumoral, endocrine. metabolic, and social factors. In the United States, according to the recent HANES survey, approximately 30 percent of middle-aged women and 15 percent of middle-aged men are obese, i.e., they weigh more than 120 percent of desired weight (Abraham and Johnson, 1979). It is generally recognized that in many persons obesity is associated with significant increases in morbidity and mortality from such diseases as hypertension, diabetes, coronary heart disease, and gall bladder disease and that mortality from these diseases is reduced with weight reduction (Dublin and Marks, 1952).
Obesity occurs in those who fail, for various reasons, to match energy intake to energy expenditure. Energy balance is most difficult to achieve when energy expenditure is low, as is generally the case in the adult population in the United States. Energy requirements vary widely among persons depending upon their age, sex, body size, and physical activity. The fixed component of energy expenditure (basal metabolic rate or BMR) is a function of body surface area and, for a given body size, varies less among individuals than does total energy expenditure. The amount of physical activity varies greatly among individuals. Furthermore, energy expenditure among individuals doing similar amounts of work is variable, suggesting that different persons perform work with different efficiencies. As people age, energy requirements decrease because of a modest fall in basal metabolic rate and a general tendency toward less physical activity. Modern life and work styles as a consequence of mechanized aids in the workplace and household, dependence on the automobile, and the popularity of such sedentary leisure activities as television viewing and spectator sports have reduced energy expenditure by the U.S. population. A recent USDA survey estimates that, in the United States, the current mean energy intake for adult men is 2,200 kilocalories and for adult women 1,500 kilocalories (Hegsted, 1979). When these data are considered in the light of the prevalence of obesity in these same groups, it appears that energy expenditure is not only low but is decreasing, on the average, in this country despite increased participation by many in exercise programs.
Achievement of weight control and reduction in the incidence of obesity should be a major objective of any set of dietary guidelines. Achievement of this objective, however, is difficult for a large number of people who resist changes in lifestyle. This is attested to by the continued high prevalence of obesity in our population despite the proliferation of weight-control programs and the continuous publication of books and articles that promise an easy road to weight reduction through diet. The high rate of failure underscores the complexity of the problem and the need for new strategies to produce sustained negative energy balances in obese persons without undue risk. Nationwide attempts to prevent obesity in children and adolescents might provide a new approach to this difficult problem.
Slimming to achieve and maintain desired weight involves long-term discipline. Fad diets promising “quick” weight loss through the use of special dietary formulas are to be avoided, because they are potentially harmful. Short-term effects observed with these diets provide no assurance of long-term attainment of desired weight. Diets restricted in energy content to below 1,200 kilocalories per day should be employed only under the guidance of a physician or other health professional.
The USDA. food guides (USDA, 1957, 1979) explain how to select foods so that essential nutrient needs can be met from a diet providing only 1,200 to 1,500 kilocalories. This is an excellent starting point for adults who wish to avoid gaining weight or for overweight persons who wish to reduce. Moderation should be the watchword in deciding the frequency and size of servings that will be needed to maintain energy balance and desired weight in sedentary persons. Moderation does not imply avoidance of any particular food, but it should be recognized that fats provide over twice as much energy per gram as do carbohydrates and proteins.
Also, those who drink alcoholic beverages must recognize that alcohol is a high-calorie food as well as a drug and that it supplies more calories (7 kcal/g) than does carbohydrate. Many Americans who drink do not do so moderately. Prudent individuals should consume no more than the equivalent of three mixed drinks a day (Ahrens et al., 1979). This is particularly true for those for whom weight control proves difficult.
A moderate increase in physical activity is equally important in slimming. Increases in energy expenditure improve physical fitness (American Medical Association, 1979), as well as contribute to mobilization of stored fat. Additional energy expenditure will permit those who are not seriously overweight to liberalize their diets without becoming obese. For those who are more obese, a consistent program of physical activity will not only increase energy expenditure, but may also facilitate control of appetite and hence food intake.
Atherosclerosis and its complications, i.e., coronary artery disease, stroke, and peripheral vascular disease, are the leading causes of death in the United States. Although the age-adjusted mortality rate from cardiovascular disease has declined 20 percent since 1960, this disorder still accounts for about 50 percent of the deaths in this country and is the leading health problem. As is true for other degenerative diseases, mortality rates from cardiovascular disease increase sharply with increasing age, 78 percent of deaths from this disease occur among those over 65 years of age (DHEW, 1979).
The causes of atherosclerosis are unknown. A number of hypotheses are being investigated in both animals and man in search of a better understanding of the factors affecting atheroma formation. High concentrations of low-density lipoproteins (LDL), enhanced platelet aggregation, transformation of smooth muscle cells, altered prostaglandin metabolism, and effects of various androgenic and estrogen steroid hormones on arterial metabolism are implicated as possible causative factors. A number of risk factors for cardiovascular disease have been identified from epidemiologic studies. These include male sex, positive family history of cardiovascular disease, hypercholesterolemia, hypertension, obesity, diabetes, cigarette smoking, and physical inactivity. Risk factors are those factors found to be statistically associated with an increased incidence of disease. They cannot, without independent evidence, be considered to be causative agents of the disease. Risk factors are “fellow travelers” that may aggravate some event in the overall pathogenesis of the disease or develop in parallel with true causes. At the present time only 50 percent of the risk of persons in the United States for coronary artery disease can be accounted for statistically by recognized risk factors (Ahrens, 1979). Thus much additional research is necessary to understand fully the multiple etiology of coronary atherosclerosis. Nonetheless, in our present state of knowledge, sound medical and public health practice should be aimed at reducing the known risk factors to the extent possible.
Diet modification as recommended for the prevention of atherosclerosis is based upon the assumption, not yet adequately tested, that reduction of high serum cholesterol levels, i.e., those greater than 250 mg/dl, will reduce the probability of cardiovascular disease (Ahrens, 1976, 1979). Total serum cholesterol is distributed among three classes of lipoproteins that accomplish the transport of cholesterol within the body. These are the very-low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). In both normal and hypercholesterolemic individuals, LDL carry the highest level of the serum cholesterol, about 65 percent. High-density lipoproteins carry the next largest quantity, about 25 percent, and the very-low-density lipoproteins carry about 10 percent (Fredrickson and Levy, 1972). These lipoprotein fractions are considered to have inherently different risk values for coronary heart disease. VLDL is essentially neutral, high LDL is a positive risk factor for atherogenesis, and high HDL is a negative risk factor, i.e., protective against atherogenesis. The concentration of HDL, which appears to be protective against atherogenesis, is higher in females and athletes, although individual responses to increased physical activity are highly variable. Heredity is important in determining the levels of various lipoprotein fractions in a given individual and the variability of the serum cholesterol response to diet. In general, dietary modifications that reduce the concentration of serum cholesterol reduce LDL concentrations.
It has been shown that modification of the diet with respect to level of fat, kind of fat, and amount of dietary cholesterol of subjects in metabolic wards under rigid dietary control can result in alterations in their serum lipid and lipoprotein concentrations (Ahrens et al., 1979). A high intake of saturated fat as a percent of calories is a major factor in elevating serum cholesterol and LDL levels. A high intake of polyunsaturated fat is important in the lowering of serum cholesterol and LDL levels. Dietary cholesterol has the least impact, particularly in the range of intake of 300-600 mg per day. In order of importance, without respect to direction of effect, the dietary factors affecting serum cholesterol concentration are saturated fat, polyunsaturated fat, and cholesterol ((Keys et al., 1965). In the diet-heart feasibility study carried out in six medical centers in the United States, using free-living populations with a controlled food supply, the effect of a low-saturated fat, high-polyunsaturated fat, low-cholesterol diet was only about 60 percent as effective in lowering serum cholesterol as it was in subjects in metabolic units (American Heart Association, 1968). Clearly, other factors in addition to adherence to diet influence serum lipid values of free-living persons in an as yet unpredictable manner.
Intervention trials in which diet modification was employed to alter the incidence of coronary artery disease and mortality in middle-aged men have been generally negative. Seven large-scale studies were carried out in London, Oslo, Helsinki, New York City, New Jersey, and Los Angeles, for 2 to 10 years on 3,060 men, 20 to 59 years of age, with or without previous myocardial infarction. In these studies, comprising about 20,000 men-years of observation, in which decreases in serum cholesterol concentrations of 7 to 16 percent occurred, there was a marginal decrease in coronary disease incidence but no effect on overall mortality. In addition, five trials involving 16,000 men for 5 years have been carried out with hypocholesterolemic drugs in England, Scotland, Europe, and the United States. The effects of the drugs on incidence of coronary artery disease were not impressive, and some unpredicted toxicities were observed (Ahrens, 1976, 1979; Report from the Committee of Principal Investigators, 1978). It appears, therefore, that although high serum cholesterol and LDL levels are positive risk factors for coronary heart disease, it has not been proven that lowering these levels by dietary intervention will consistently affect the rate of new coronary events.
Despite these generally unimpressive results, some organizations (American Heart Association, 1961. 1978; Select Committee on Nutrition and Human Needs, 1977) have recommended that dietary lipids be reduced from 40 percent to about 30 percent of calories and that the ratio of polyunsaturated to saturated fat (P:S ratio) be changed from the present value in the American diet of 0.4 to 0.5 to a ratio of about 1.0, in order to achieve lower serum cholesterol levels in the population generally. Unfortunately, the benefit of altering the diet to this extent has not been established. As noted, other studies employing diets containing 35-40 percent of calories from fat and higher P:S ratios have shown equivocal effects on coronary disease and have been accompanied by a somewhat greater incidence of gastrointestinal disease (Ahrens, 1976).
In the light of these observations, the Board recommends that the fat content be adjusted to a level appropriate for the caloric requirements of the individual. Infants, adolescent boys, pregnant teenage girls, as well as adults performing heavy manual labor, probably have no need to reduce the fat level of their diets below 40 percent of calories. On the other hand, sedentary persons attempting to achieve weight control may be well advised to reduce the caloric density of their diets by reduction of dietary fat. It does not seem prudent at this time to recommend an increase in the dietary P:S ratio except for individuals in high-risk categories. The average intake of polyunsaturated fatty acids in this country is 6-7 percent of calories, which provides about five times the nutritional requirement for essential fatty acids.
The intake of dietary cholesterol by the U.S. population averages about 450 mg per day at the present time, ranging from 200 to 1,500 mg (Nichols et al., 1976; Hegsted, 1979). Between 1900 and 1970, the average intake of cholesterol varied from 509 to 576 mg/day (Gortner, 1975; Ahrens and Boucher, 1978). The present lower value reflects a decrease in total caloric intake by the U.S. population during the past decade. Cholesterol is an essential metabolite and is actively synthesized by the human body in amounts of 800 to 1,500 mg daily. In contrast to many species, man absorbs cholesterol poorly, permitting the entry of only 10-50 percent of that in the diet (Dietschy and Wilson, 1970). There is a curvilinear relationship between dietary cholesterol intake and serum cholesterol concentration in man, as evidenced by a slope that decreases with increasing cholesterol intake from about 12 mg/dl of serum cholesterol/100 mg dietary cholesterol/1,000 calories at low levels to less than 2 mg/dl/100 mg/1,000 calories at high levels (Keys et al., 1965; Ahrens et al., 1979). This effect is due to the poor absorption of cholesterol at high levels, plus feedback mechanisms in the body that adjust biosynthesis to body needs. No significant correlation between cholesterol intake and serum cholesterol concentration has been shown in free-living persons in this country (Kannel and Gordon, 1970; Nichols et al., 1976). For these reasons the Board makes no specific recommendations about dietary cholesterol for the healthy person. Similar conclusions were reached by the Canadian Health Protection Branch (Department of National Health and Welfare. 1977).
For persons with a positive family history of heart disease and other risk factors, such as obesity, hypertension, and diabetes , concentrations of blood lipids and lipoprotein fractions should be determined and, if any are abnormal, therapy should be undertaken under a physician’s guidance.
A relationship between the intake of salt and the development of hypertension was emphasized as early as 1904 by Ambard and Beaujard (1904). In 1950 Dahl and a group of collaborators at the Rockefeller Institute carried out a series of investigations demonstrating that the principal reason for the effect of the rice diet (Kempner, 1948) in reducing hypertension was its low salt content (Dole et al., 1951; Dahl, 1972). The low-protein content of this diet may also be contributory. According to Freis (1976), increased extracellular fluid volume is the most significant factor initiating the sequence of events leading to chronic hypertension. Low-sodium diets reduce extracellular fluid volume, and the chlorothiazide diuretics appear to act in a similar manner.
The nutritional requirement for sodium for growth and for unavoidable losses from skin and feces is in the range of 4-8 mEq or 100-200 mg of sodium per day (equivalent to 250-500 mg of salt per day). Hypertension is absent in some nonindustrialized populations in the Solomon Islands, the Amazon basin, and the Coco Islands of Polynesia, where the salt intake is about 2 g per day (FNB, 1979). The incidence is high in populations in northern Japan, where salt intake commonly exceeds 20-25 g/day. Available evidence indicates that sodium restriction to approximately 3.8 g of salt per day will effect a slight reduction (5 mm Hg) in blood pressure among moderately hypertensive adults (Parijs et al., 1973). Several very carefully controlled studies of severely hypertensive adults have shown that sodium must be restricted to 200 mg (0.5 g salt) per day in order to achieve a significant reduction in blood pressure (Kempner, 1948). The level of dietary sodium chloride that will permit the development of hypertension in the 15-20 percent of the population that have a genetic predisposition for this condition is unknown. Studies in animals show that genetically predisposed rats develop hypertension when fed high levels of sodium chloride (Meneely and Battarbee, 1976). Genetic variations in man are large, however and an association between blood pressure and salt intake has not been demonstrated within selected U.S. populations. The average sodium chloride intake in this country is about 10 g per day. with a range of 4-25 g. This average intake .of salt is 20 times the nutritional requirement.
Hypertension is also known to be associated with obesity, and a number of studies have demonstrated that weight reduction is associated with a decrease in blood pressure. The extent to which decreased sodium intake is a factor in these cases is still controversial, although it has recently been reported that weight reduction exerts an independent effect (Reisin et al., 1978). In a study of 10,900 persons, the National Heart, Lung and Blood Institute recently reported that concerted antihypertensive drug therapy, combined with advice to avoid salty food, resulted in a 17 percent reduction in mortality from those chronic diseases for which hypertension is a risk factor (National Heart, Lung and Blood Institute, 1979).
The Board believes that sodium chloride intakes of many people in this country are excessive, particularly in that 15 percent of the American population at risk for hypertension. There is no reason to believe that reduction of sodium chloride intake to levels of 3 g per day would be harmful for healthy persons, and it may be helpful for the prevention of hypertension in susceptible individuals for whom salt is a permissive factor. Achieving an intake of 3 g of salt per day would require elimination of salt in cooking and at the table since nondiscretionary salt intake in foods amounts to at least 3 g per day (FASEB, 1978).
Cancer is the second leading cause of death in the United States. A putative relationship between diet and cancer implicating “lifestyle” factors in addition to smoking has been proposed on the basis of epidemiologic and experimental observations. However, for the most part, specific causative agents that can be related to have not been identified. Foods contain both nutritive and nonnutritive components. Most of the latter are present naturally, but same are added during formulation, processing, and cooking. Studies have shown that some specific nonnutritive substances can promote tumor development in animals. For example, aflatoxin, a potent carcinogen derived from mold on grains. legumes, or nuts, is a “naturally occurring” toxin in these foods. For decades. sodium nitrite has been added to cured meats at levels of about 200 parts per million to prevent botulism. Since nitrite can react with secondary amines to form carcinogenic nitrosamines, the question of the safety of nitrites in amounts present in cured meats has been raised (Issenberg, 1976) and is currently under review. The average nitrate intake from mixed diets in the United States is 100-200 mg daily, and the intake of performed nitrite as food additives is about 3 mg. Bacteria in the mouth or intestine, however, reduce nitrate to nitrite in appreciable amounts, so that up to 100 mg may be formed daily (National Academy of Sciences, 1979).
The situation regarding nutritive elements in the U.S. diet is complex. Certain tumors, such as those of the breast and uterus, are associated with obesity in human beings (MacMahon et al., 1970). Studies have shown that tumor incidence in animals may be decreased in some circumstances by restricting calories, fats (particularly polyunsaturated fats), and protein (Tannenbaum and Silverstone, 1953; Carroll and Khor, 1971). From epidemiologic observations, associations between high-calorie, high-fat, and low-fiber diets and cancer of the colon have been reported (Wynder, 1978). These effects are assumed to be related to metabolites produced by intestinal bacteria that can be modified by a change in the composition of the diet. It has been suggested that some of these metabolic products may be mutagens that are potential carcinogens, but there is no current evidence to support this view. Further study of bacterial metabolism in the gut under various dietary conditions favoring tumorigenesis is needed.
The Board believes that in the absence of evidence of a causal relationship between the macronutrients of the diet and cancer, there is no basis for making recommendations to modify the proportions of these macronutrients in the American diet at this time. Although the recommendations reflected therein are slightly different, the recent statement on diet and cancer from the National Cancer Institute also recognized that no direct cause-effect relationship has been observed for nutrition and cancer in humans (Upton, 1979). It is possible that the correlation between high-fat diets and colon cancer may reflect on a high energy intake leading to overweight or some other diet-related variable. Clearly, a nutritious diet providing adequate amounts of all nutrients and the proper energy content to achieve desirable weight is important for general health and for vigorous defense mechanisms against cancer as well as other diseases.
Diabetes mellitus is not a single disease but rather a syndrome of hyperglycemia and glycosuria, accompanied by varying degrees or ketosis and acidosis, with or without weight loss. It has several causes and mechanisms of inheritance. Juvenile diabetes occurs in young people because of a failure of the pancreas to secrete insulin in adequate amounts and represents an insulin deficiency. Ketoacidosis and weight loss due to catabolism of fat and protein are common in this form of the disease. Late onset of diabetes in adults after age 40 does not usually result from insulin deficiency, but is strongly associated with obesity and appears to result from an alteration in insulin receptors. Severe ketosis is not common in this form of diabetes.
Epidemiological studies are not consistent with the hypothesis that high sugar consumption is a cause of diabetes mellitus (Medalie et al., 1975). The Pima Indians of Arizona, for example, have a prevalence of adult-onset diabetes that is among the highest in the world, but their intake of sugar is considerably lower than that of the average American (Bennett et al., 1976). There is evidence that genetic factors are important in the development of diabetes in the Pima and in the development of noninsulin-dependent diabetes generally. High-carbohydrate diets have been reported to increase the glucose tolerance of mild late-onset diabetics (Brunzell et al., 1971). It has been shown that increasing the ratio of “complex” carbohydrates to simple sugars in the diet improves glucose tolerance in diabetic individuals (Crapo et al., 1976). In addition, it has been shown that such viscous soluble fibers as metamucil, pectin, and guar further improve glucose tolerance and reduce insulin requirements in diabetics (Jenkins, 1979). For this reason, persons with factors predisposing to diabetes, including obesity, might well increase the consumption of foods containing “complex” carbohydrates and soluble plant fibers at the expense of simple sugars. A ratio between “complex” carbohydrates and simple sugars of between 1:1 and 2:1 in the diet could be beneficial for persons with diabetes. Excessive caloric intake should be avoided and an adequate level of physical activity maintained. In juvenile diabetics, blood sugar levels should be maintained within normal limits by judicious use of insulin, diet and exercise. Late-onset, obese diabetic subjects in general do not require exogenous insulin and should be regulated with diet and a program of physical activity (Cahill et al., 1976).
Even though coronary artery disease and other manifestations of atherosclerosis are more common in diabetic persons than others, there is no convincing evidence that fasting serum cholesterol and lipoprotein levels are higher in well-regulated diabetic men than in normal men (Bennion and Grundy, 1977).
The Board recommends that careful regulation of diabetes with a diet containing more complex carbohydrates, insulin (if necessary), and exercise to achieve normal weight and blood sugar levels is important to extend life and minimize the complications of the disease, including atherosclerosis.
DECISION-MAKING IN PUBLIC HEALTH
Good public health practice depends upon the application of sound principles of preventive medicine to population groups. One of these principles is that primary prevention of disease is preferable to treatment, provided the preventive intervention is effective and safe. Another is that primary prevention is preferable to secondary prevention, i.e., the prevention of the progression of a disease, once established. Immunization of healthy persons against preventable infectious diseases is a classic example of primary prevention and constitutes good public health practice. It is clear that risk-benefit considerations for proposed new interventions constitute an important aspect of decision making in public health.
Any public official considering a new public health program for disease prevention must evaluate the potential effectiveness of the proposed action before recommending its adoption. If there is uncertainty about its effectiveness, there must be clear evidence that the proposed intervention will not be harmful or detrimental in other ways. In the case of diseases with multiple and poorly understood etiology, such as cancer and cardiovascular disease, the assumption that dietary change will be effective as a preventive measure is controversial. These diseases are not primarily nutritional, although they have nutritional determinants that vary in importance from individual to individual. Authorities who resist recommendations for diet modification express a legitimate concern about promising tangible benefits from controversial recommendations that alter people’s lives and habits. Many also have an equally valid concern about diverting attention and resources away from investigation of the underlying causes of these diseases toward unproven action programs. Those experts who advocate a more aggressive approach and seek to change the national diet in the hope of preventing these degenerative diseases assume that the risk of change is minimal and rely heavily on epidemiologic evidence for support of their belief in the probability of benefit. Neither the degree of risk nor the extent of benefit can be assumed in the absence of suitable evidence.
The Board has debated its recommendations in the light of these considerations. It believes that an extensive and critical evaluation of assumptions underlying any recommendations for dietary change should be carried out, including risk-benefit analyses. It is aware that changes in the American food supply are occurring spontaneously and continuously due to innovations by the food industry, impact of advertising, and consumer preferences. The subject of dietary guidelines will be under continuing study by the Board, and reports will be issued periodically in the future.
CONCLUSIONS AND RECOMMENDATIONS
In a sound program of preventive medicine, appropriate nutritional guidance is an essential part of a comprehensive plan involving immunization, improvement of physical fitness, prevention of accidents, and avoidance of cigarette smoking and alcohol abuse. Individual variation in human populations with respect to susceptibility to the chronic degenerative diseases is large; therefore, surveillance of risks by health professionals is recommended for all healthy persons. Each individual should be aware of his personal metabolic risk factor profile, which includes assessment of hyperglycemia, hypercholesterolemia, hypertension, and family history. The Board expresses its concern over excessive hopes and fears in many current attitudes toward food and nutrition. Sound nutrition is not a panacea. Good food that provides appropriate proportions of nutrients should not be regarded as a poison, a medicine, or a talisman. It should be eaten and enjoyed.
In view of these premises, the Board makes the following recommendations to adult Americans. It believes that these guidelines will improve general nutritional status, may be beneficial in preventing or delaying the onset of some chronic degenerative diseases, and incur no appreciable risks. Recommendations for infants and children and for pregnant and lactating worsen have been made previously (FNB, 1980).
- Select a nutritionally adequate diet from the foods available, by consuming each day appropriate servings of dairy products, meats or legumes, vegetables and fruits, and cereal and breads.
- Select as wide a variety of foods in each of the major food groups as is practicable in order to ensure a high probability of consuming adequate quantities of all essential nutrients.
- Adjust dietary energy intake and energy expenditure so as to maintain appropriate weight for height; if overweight, achieve appropriate weight reduction by decreasing total food and fat intake and by increasing physical activity.
- If the requirement for energy is low (e.g., reducing diet) , reduce consumption of foods such as alcohol, sugars, fats, and oils, which provide calories but few other essential nutrients.
- Use salt in moderation; adequate but safe intakes are considered to range between 3 and 8 g of sodium chloride daily.
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