The American Cancer Society (ACS) has issued its 2002 update on guidelines for reducing the risk of cancer with healthy food choices and physical activity. The full report appears in CA: A Cancer Journal for Clinicians, March/April 2002.

These guidelines are developed and published every five years by a national panel of experts in cancer research, prevention, epidemiology, public health, and policy. Recognizing that the ability to make healthy choices is often affected by factors within the environment in which people live, work, and play, the panel tried to identify key social and structural factors that influence access to resources for an active lifestyle. This year, the committee adds a recommendation for community action to accompany the four recommendations for individual choices for nutrition and physical activity.

In the United States, evidence suggests that one third of the more than 500,000 cancer deaths that occur each year can be attributed to diet and physical activity habits. The relative strength of current scientific evidence linking major components of diet to common cancer sites is summarized in the accompanying table.

Recommendations for Community Action

According to the ACS, most Americans would like to have a healthier lifestyle, but many encounter social, economic, and cultural barriers that make it difficult to follow diet and activity guidelines. Longer workdays and more homes with multiple wage earners reduce the time available for meal preparation and leisure activities. This results in a shift toward eating more fast food and leading a more sedentary lifestyle.

The ACS suggests that public, private, and community organizations work to create social and physical environments that support the adoption and maintenance of healthful nutrition and physical activity behaviors. Facilitating these changes will require increased access to healthy foods in schools, at work, and in the community. Efforts also are needed to provide safe and accessible environments for physical activity and transportation to and from these areas.

Recommendations for Individual Choices

In the United States, about 35 percent of cancer deaths may be avoidable through dietary modification. Epidemiologic studies have shown that populations with diets high in fruits and vegetables and low in animal fat, meat, or calories have a reduced risk of some of the most common types of cancer. The panel focuses on the following recommendations:

• Eat a variety of healthy foods, with an emphasis on plant sources. Eat five or more servings of a variety of vegetables and fruits every day in various forms (fresh, frozen, canned, dried, and juiced); limit french fries, snack chips, and other fried vegetable products; choose 100 percent juice if you drink fruit or vegetable juices. Greater consumption of fruits and vegetables has been associated with a lower risk of lung, oral, esophageal, stomach, and colon cancer.

Choose whole grain rice, bread, pasta, and cereals; limit consumption of refined carbohydrates, including pastries, sweetened cereals, soft drinks, and sugars. Whole grains are an important source of vitamins and minerals associated with lower risk of colon cancer, such as folate, vitamin E, and selenium. They are higher in fiber and other nutrients than refined flour products. Beans are particularly rich in nutrients that may protect against cancer, and are a low-fat, high-protein alternative to meat.

Limit consumption of red and processed meats, especially those high in fat. Choose fish, poultry, or beans as an alternative to beef, pork, and lamb; when eating meat, select lean cuts and have smaller portions, using meat as a side dish; prepare meat by baking, broiling, or poaching, rather than frying or charbroiling, to reduce the overall fat content. High-fat diets have been associated with an increase in risk for cancer of the colon, rectum, prostate, and endometrium. Choose lean meats and lower-fat dairy products, and substitute vegetable oils for butter or lard.

• Adopt a physically active lifestyle. Adults should engage in at least moderate activity for 30 minutes or more on five or more days a week. Forty-five minutes or more of moderate-to-vigorous activity a week may further enhance reductions in the risk of breast and colon cancer.

Children and adolescents should have at least 60 minutes a day of moderate-to-vigorous physical activity for at least five days a week. This should be encouraged because one of the best predictors of adult activity is activity levels during childhood and adolescence, and because of the critical role activity plays in maintaining a healthy weight.

Regular activity helps maintain a healthy body weight by balancing caloric intake with energy expenditure. Moderate-to-vigorous activity is needed to metabolize stored body fat and to modify physiologic functions that affect insulin, estrogen, androgen, prostaglandins, and immune function. Physical activity accelerates the movement of food through the intestine, reducing the length of time that the bowel lining is exposed to mutagens, may decrease the exposure of breast tissue to circulating estrogen, and improves energy metabolism and reduces circulating concentrations of insulin and related growth factors.

Moderate activities require effort equivalent to a brisk walk. Vigorous activities engage large muscle groups and cause an increase in heart rate, breathing depth and frequency, and sweating. Men older than 40 years, women older than 50 years, and people with chronic illnesses should consult their physicians before starting a vigorous exercise program. To reduce risk of musculoskeletal injuries, stretching and warm-up periods should be part of each program.

• Maintain a healthy weight throughout life. Current trends indicate that the largest percentage of calories in the American diet come from foods high in fat, sugar, and refined carbohydrates. Limiting portion sizes, especially of these types of foods, is another important strategy to reduce total caloric intake. Meals in restaurants typically exceed the portion sizes needed to meet recommended daily caloric intake. Balance caloric intake with physical activity and lose weight if currently overweight or obese. Obesity is a major risk factor for cancer, diabetes, stroke, and coronary heart disease.

• If you drink alcoholic beverages, limit consumption. Men should limit themselves to two drinks per day and women to one drink per day. A drink is defined as 12 oz of beer, 5 oz of wine, or 1.5 oz of 80-proof distilled spirits. Alcohol consumption is an established cause of cancers of the mouth, pharynx, larynx, esophagus, liver, and breast. The risk increases substantially with intake of more than two drinks per day.

Factors Affecting Risk for the Most Common Cancers

Currently, the best advice is to consume antioxidants through food sources rather than supplements.

BLADDER CANCER

The major risk factors for bladder cancer are smoking and exposure to certain industrial chemicals. Limited evidence suggests that drinking more fluids and eating more vegetables may lower the risk of bladder cancer.

BRAIN CANCER

There are no known nutritional risk factors for brain cancer.

BREAST CANCER

Risk is increased by several factors that cannot be easily modified: menarche before 12 years of age, nulliparity or first birth at 30 years or older, late age at menopause, and a family history of breast cancer. Risk can be reduced by limiting the use of hormone replacement therapy, avoiding obesity, staying physically active, and breastfeeding. The best nutritional advice is to engage in vigorous activity at least four hours a week, avoid or limit alcoholic beverages to no more than one a day, and minimize lifetime weight gain.

COLORECTAL CANCER

Risk of colorectal cancer is increased in those with a family history, with the use of tobacco, and possibly with excessive alcohol consumption. Obesity and diets high in red meat have also been associated with increased risk of colon cancer. Risk may be decreased by using aspirin or other nonsteroidal anti-inflammatory drugs and, possibly, hormone replacement therapy. Diets high in vegetables and fruits have been associated with decreased risk. Increasing evidence suggests that vigorous activity may have an even greater benefit in reducing risk than regular moderate exercise.

ENDOMETRIAL CANCER

To reduce the risk of endometrial cancer, maintain a healthy weight through diet and regular exercise, and eat at least five servings of fruits and vegetables a day.

KIDNEY CANCER

The best way to reduce the chances of kidney cancer is to avoid becoming overweight.

LEUKEMIAS AND LYMPHOMAS

There are no known nutritional factors for decreasing the risk for leukemias or lymphomas.

LUNG CANCER

Currently, the best advice to reduce risk of lung cancer is to avoid exposure to tobacco and to eat at least five servings of fruits and vegetables a day.

ORAL AND ESOPHAGEAL CANCERS

Avoid all forms of tobacco, restrict alcohol consumption, avoid obesity, and eat at least five servings of vegetables and fruits a day.

OVARIAN CANCER

There are no firmly established nutritional risk factors for ovarian cancer, but vegetable and fruit consumption may lower risk.

PANCREATIC CANCER

Avoid tobacco use, maintain a healthy weight, remain physically active, and eat five or more servings of fruits and vegetables a day.

PROSTATE CANCER

To reduce risk, limit intake of animal-based products, especially red meats and high-fat dairy products, and eat five or more servings of fruits and vegetables a day.

STOMACH CANCER

To reduce risk, eat at least five servings of fruits and vegetables a day.

Other Dietary Factors Affecting Cancer Risk

The following points address concerns about diet and physical activity in relation to cancer.

• There is currently no evidence that the substances found in bioengineered foods now on the market are harmful or that they would increase or decrease cancer risk because of the added genes.

• Men and women should try to get recommended levels of calcium primarily through food sources.

• There is no evidence that lowering blood cholesterol levels has an effect on cancer risk.

• There is no evidence that caffeine use increases the risk of cancer.

• Fluorides do not increase cancer risk.

• Folic acid deficiency may increase the risk of colorectal and breast cancer. To reduce this risk, folic acid is best obtained through eating vegetables, fruits, and enriched grain products.

• Additives are usually present in very small quantities in food, and no convincing evidence exists that any additive consumed at these levels causes human cancers.

• Insufficient evidence exists to support a specific role for garlic in cancer prevention.

• Radiation does not remain in the foods after treatment, and there is no evidence that eating irradiated foods increases cancer risk.

• Even if lycopene in foods is associated with lower risk for cancer, it does not follow that high doses taken as supplements would be more effective or safe.

• Consumption of meats preserved by methods using smoke or salt increases exposure to potentially carcinogenic chemicals and should be minimized. Braising, steaming, poaching, stewing, and microwaving meats minimize the production of these chemicals. Microwaving and steaming may be the best ways to preserve the nutritional content in vegetables.

• Consumption of olive oil is not associated with any increased risk of cancer.

• At present, no research exists to demonstrate whether organic foods are more effective in reducing cancer risk than are similar foods produced by other farming methods.

• There is no evidence that residues of pesticides and herbicides at the low doses found in foods increase the risk of cancer.

• There is no evidence that phytochemicals taken as supplements are as beneficial as the vegetables, fruits, beans, and grains from which they are extracted.

• No evidence suggests that salt used in cooking or in flavoring foods affects cancer risk.

• There is a narrow margin between safe and toxic doses of selenium. The maximum dose in a supplement should not exceed 200 mcg per day. Seafood, meats, and grain products are good sources of selenium.

• There is no convincing data that soy supplements are beneficial in reducing cancer risk.

• Food is the best source of vitamins and minerals, not supplements. If a supplement is taken, the best choice is a balanced multivitamin/mineral supplement containing no more than 100 percent of the daily value of most nutrients, because high doses of some nutrients can have adverse effects.

• Tea has not been proven to reduce cancer risk in humans. The few studies in which vitamin C has been given as a supplement have not shown a reduced risk of cancer.

• Recent evidence demonstrates that trans-fats have adverse cardiovascular effects, such as raising blood cholesterol levels, but their relationship to cancer risk has not been determined.

• Drinking at least eight cups of liquid a day is usually recommended, and some studies indicate that even more may be beneficial.