Guidelines on diet, nutrition, and cancer prevention: reducing the risk of cancer with healthy food choices and physical activity. The American Cancer Society 1996 Advisory Committee on Diet, Nutrition, and Cancer Prevention

Abstract

The American Cancer Society publishes nutrition guidelines to advise the public about dietary practices that reduce cancer risk.1 These guidelines are developed by expert advisory committees and are based on existing scientific evidence that relates diet and nutrition to cancer risk in human population studies as well as in laboratory experiments. This evidence suggests that about one third of the 500,000 cancer deaths that occur in the United States each year is due to dietary factors. Another third is due to cigarette smoking. Therefore, for the large majority of Americans who do not smoke cigarettes, dietary choices and physical activity become the most important modifiable determinants of cancer risk.2 The evidence also indicates that although genetics is a factor in the development of cancer, cancer cannot be explained by heredity alone. Behavioral factors such as cigarette smoking, dietary choices, and physical activity modify the risk of cancer at all stages of its development. The introduction of healthful diet and exercise practices at any time from childhood to old age can promote health and reduce cancer risk. On the basis of its review of the scientific evidence, the American Cancer Society 1996 Advisory Committee on Diet, Nutrition, and Cancer Prevention reaffirms previous conclusions of the Society that dietary practices and physical activity—along with smoking cessation, avoidance of occupational carcinogens, and early detection—are important factors in the prevention of cancer and cancer death. Many dietary factors can affect cancer risk: types of foods, food preparation methods, portion sizes, food variety, and overall caloric balance. Cancer risk can be reduced by an overall dietary pattern that includes a high proportion of plant foods (fruits, vegetables, grains, and beans); limited amounts of meat, dairy, and other high-fat foods; and a balance of caloric intake and physical activity. Many Americans do not follow such healthful practices. Indeed, trends indicate an increase in caloric intake, greater use of high-fat convenience foods, and a decline in physical activity among Americans.3 We believe that such unhealthful trends are due in part to shifts toward consumption of food outside the home, to more sedentary lifestyle patterns, and to the advertising and promotion of high-calorie foods.4 The committee is especially concerned about the effects of such trends on the long-term health of children, who are establishing lifetime patterns of food intake and physical activity.5 In this report, the committee presents four broad guidelines to reduce cancer risk among people aged two years and older (Table 1). In addition, we offer advice on a wide variety of questions about nutrition and cancer that concern the public at large. These recommendations represent the committee's best efforts to provide advice based on scientific studies related specifically to the primary prevention of cancer. This advice does not apply to cancer treatment or to reducing the risk of cancer recurrence. The committee's recommendations are consistent in principle with the 1992 Food Guide Pyramid,6 the 1995 Dietary Guidelines for Americans,7 and dietary recommendations of other agencies for general health promotion and for the prevention of coronary heart disease, diabetes, and other diet-related chronic conditions.8-11 Although the committee recognizes that no diet can guarantee full protection against any disease, we believe that our recommendations offer the best nutrition information currently available to help Americans reduce their risk of cancer. The evidence is particularly strong that increased consumption of fruits and vegetables reduces the risk of colon cancer. Include fruits or vegetables in every meal. Choose fruits and vegetables for snacks. Include grain products in every meal. Choose whole grains in preference to processed (refined) grains. Choose beans as an alternative to meat. The scientific basis for these recommendations is very strong for cancers at many sites, particularly for cancers of the gastrointestinal and respiratory tracts.12-15 The evidence is particularly strong that increased consumption of fruits and vegetables reduces the risk of colon cancer.16 Evidence is less strong for cancers considered hormonal, such as breast and prostate cancer. Of the many scientific studies on this subject, the great majority show that eating fruits and vegetables (especially green and dark yellow vegetables and those in the cabbage family, soy products, and legumes) protects against colon cancer. Greater consumption of vegetables, fruits, or both together has also been associated with a lower risk of lung cancer.17 The major risk factor for lung cancer is tobacco, but diet also affects risk. Studies have shown that people who smoke cigarettes tend to eat less healthful diets than nonsmokers, but fruits and vegetables reduce cancer risk whether or not people smoke. Because many studies indicate that foods high in beta carotene protect against lung cancer, scientists have suggested that beta carotene itself might reduce lung cancer risk. Recent clinical trials of beta carotene supplements, however, have shown that smokers taking the supplement developed lung cancer at higher rates than those taking a placebo.18, 19 These findings support the idea that beta carotene may be a proxy for other protective nutrients or substances, singly or in combination, within foods. They also suggest that taking a single nutrient in large amounts may produce adverse effects. Despite the strength of the evidence associating consumption of fruits and vegetables with decreased cancer risk, intake of these foods is low among many adults and children.20 Concern about low intake levels has led to a country-wide initiative—the National 5 A Day for Better Health Program—to increase fruit and vegetable intake to five or more servings of fruits and vegetables daily.21 This recommendation applies to foods in their fresh, frozen, canned, dried, or juice forms, but does not apply to specific nutrients or other substances that might be extracted from them. Vegetables and fruits are complex foods containing more than 100 beneficial vitamins, minerals, fiber, and other substances. Scientists do not yet know which of the nutrients or other substances in fruits and vegetables may be protective against cancer. The principal possibilities include specific vitamins and minerals, fiber, and phytochemicals—carotenoids, flavonoids, terpenes, sterols, indoles, and phenols—that are present in foods of plant origin.12, 14 How fruits and vegetables exert their protective effects constitutes an active area of scientific inquiry. Until more is known about specific food components, the best advice is to eat 5 or more servings of fruits and vegetables each day. Grains such as wheat, rice, oats, barley, and the foods made from them constitute the base of healthful diets as illustrated in the Food Guide Pyramid.6 Healthful diets contain six to 11 standard servings of foods from this group each day. As shown in Table 2, standard portion sizes are defined as quite small, and this number of servings is not difficult to achieve. Grains are an important source of many vitamins and minerals such as folate, calcium, and selenium, all of which have been associated with a lower risk of colon cancer.16 Whole grains are higher in fiber and certain vitamins and minerals than refined flour products. Because the benefits of grain foods may derive from their other nutrients as well as from fiber,22 it is best to obtain fiber from fruits, vegetables, and whole grains rather than from fiber supplements. Beans are excellent sources of many vitamins and minerals, protein, and fiber. Beans are legumes, the technical term for the family of plants that includes dried beans, pinto beans, lentils, and soybeans, among many others. Beans are especially rich in nutrients that may protect against cancer23 and can be a useful low-fat but high-protein alternative to meat. Replace fat-rich foods with fruits, vegetables, grains, and beans. Eat smaller portions of high-fat foods. Choose baked and broiled foods instead of fried foods. Select non-fat and low-fat milk and dairy products. When you eat packaged, snack, convenience, and restaurant foods, choose those low in fat. When you eat meat, select lean cuts. Eat smaller portions of meats. Choose beans, seafood, and poultry as an alternative to beef, pork, and lamb. Select baked and broiled meats, seafood, and poultry, rather than fried. High-fat diets have been associated with an increase in the risk of cancers of the colon and rectum,16 prostate,24 and endometrium.25 The association between high-fat diets and breast cancer is much weaker.26 Whether these associations are due to the total amount of fat, the particular type of fat (saturated, monounsaturated, or polyunsaturated), the calories contributed by fat, or some other factor in food fats has not yet been determined. Because a gram of fat contains more than twice the calories of a gram of protein or carbohydrate (9 versus 4 kcal/gram), studies cannot easily distinguish the effects of fat itself from effects of the calories it contains. Moreover, people who eat high-fat diets tend to be heavier and to eat more meat and fewer fruits and vegetables, so their risk of cancer also is increased for other from sources major of total fat, fat, and in the American Although are sources of protein and many important vitamins and minerals, consumption of pork, been to cancers at sites, most colon and How much of the association between and cancer is due to total fat or fat, and much is due to other of meat or the diet is at in to fat, such as which are protein is may help the association between meat and colon cancer. monounsaturated, and fats all the number of but may affect cancer risk in the effects of specific such as those from vegetable or may in their effects on cancer risk. This of types of fat to cancer risk is active High-fat diets have been associated with an increase in the risk of cancers of the colon and and evidence indicates that fat may be particularly important in the risk for cancer as well as for heart The best to reduce fat intake is to choices in the and preparation of foods. Choose lean and dairy products, and vegetable for or Food can be a useful to foods lower in fat. Choose smaller portions and use meat as a rather than as the of a meal. beans, grains, and vegetables in to help dietary patterns to include more foods from plant rather than are also and foods, rather than reduces the overall amount of fat in These recommendations for cancer prevention are consistent with dietary advice to reduce at active for or more on most of the within activity can help protect against some by caloric intake with or by other of caloric intake and can to and increased risk for cancers at colon and rectum,16 prostate,24 breast and These findings are by and by studies an association between physical activity and a reduced risk of some may or it may in other to reduce cancer risk. breast and prostate cancer, physical activity may effects on colon cancer, physical activity the reducing the of time that the is to physical activity and caloric intake are to or to a The for and of all a within to reduce the risk for chronic such as coronary heart and as well as cancer. physical activity may increase caloric and people to more healthful fruits, vegetables, grains, and a The for and Prevention and the American of a National of Health and the of physical activity each as a to promote The does not to be to be and can be by for about two or by a variety of other and at a of to Studies suggest that people reduce their cancer caloric intake and increase physical activity. 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The for this is but the association may be due to of or its to in levels of such as or to some other may have effects on cancer risk. calories but people who may be for foods. of the studies suggest that the risk of breast cancer may increase with an intake of a intake of has been shown to the risk of coronary heart disease, at in These benefits may the risk of cancer in older than years and in older than health advise people who to their intake to two a for and one for less well than as a of smaller and greater to with an high risk for breast cancer might from and and people taking certain also from cancer is the for cancer among American and is to lung cancer in cancer cancer is by factors that affect levels age at number of breast and physical activity. Many studies suggest that may increase the risk of breast in studies suggest that diets high in fruits and vegetables the risk of breast cancer, although this evidence is much than that for other cancer the present the best advice to reduce the risk of breast cancer is to intake of eat a diet rich in fruits and vegetables, be and cancers are the of cancer among high in foods from plant sources fruits, whole grains, have been associated with a decreased risk, diets high in fat and meat have been associated with an increased risk of cancer. and physical also to increase risk. the best to reducing the risk of cancer is to fewer high-fat foods, intake of meats, eat more vegetables, fruits, and whole grains, be and Studies of cancer that risk. The association may be due to the increase in levels that among who are reduce the risk of cancer, a physical activity and food cancer is the of cancer among than of lung cancer occur as a of smoking. Many studies have that the risk of lung cancer among both smokers and is lower among people who amounts of fruits and reduce the risk of lung cancer, do not smoke tobacco, and eat at five servings of vegetables and fruits every cigarettes, tobacco, and singly and increase the risk of cancers of the and amounts of fruits and vegetables that risk. protect against these do not use in any do not more than one or two each and eat at five servings of fruits and vegetables each cancer is the cancer among American Scientists know that prostate cancer is related to but are as to the of fat, meats, and dairy products has been to be associated with an increase in the risk of prostate cancer, a for reduce the risk of prostate cancer, intake of foods from especially fats and meats. 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