Groups Issue Report on Diet, Weight, Exercise, and Cancer Risk
Maintain a healthy body weight. Fill your plate with vegetables and fruit and say no to sugary soft drinks. Get off the couch and take a walk. Public health advocates have long promoted such healthy lifestyle recommendations to prevent chronic conditions such as diabetes and heart disease. Now a report by the American Institute for Cancer Research and the World Cancer Research Fund, Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective, concludes that following the same advice is likely to significantly reduce cancer risk as well.
The report - a comprehensive review of the scientific evidence linking cancer to diet, physical activity, and weight - finds convincing evidence that obesity is a cause of colorectal, endometrial, esophageal, kidney, liver, pancreatic, and postmenopausal breast cancer; that abdominal obesity, in particular, causes colorectal cancer; and that consumption of red and processed meat such as bacon, ham, pastrami, and salami, also causes colorectal cancer.
Its recommendations for reducing cancer risk include avoiding weight gain and increases in waist size, getting at least 30 minutes of physical activity every day, limiting red meat consumption to 18 oz. of cooked meat per week (about 2.5 oz. per day), and eating very little, if any, processed meat.
"This is the largest, most systematic review of the role of diet in cancer prevention that has been conducted to date," says Dr. Arthur Schatzkin of NCI's Division of Cancer Epidemiology and Genetics, a member of the international expert panel that distilled the evidence and formulated the recommendations.
Five years in the making, the report is the outcome of a process that involved 9 teams of scientists from around the world, who evaluated more than 7,000 studies on diet, physical activity, weight management, and cancer.
Among the report's conclusions is that cancer risk increases by 15 percent for every 1.7 oz. of red meat consumed per day beyond the recommended limit of 18 oz. per week. Dr. Schatzkin notes that, for an individual, this is a relatively modest increase in risk. By contrast, a person who smokes two packs of cigarettes a day may increase their cancer risk by as much as 2,000 percent compared with that of a nonsmoker.
"At the population level, however, these apparently modest risks have substantial health effects," Dr. Schatzkin explains. "Because many people eat red and processed meat and many are obese, the burden of cancer attributable to these nutritional factors may be substantial. If we could reduce the incidence of, say, breast cancer or colorectal cancer by 15 percent, that would mean preventing a significant amount of disease and death."
The report finds convincing evidence that having children and breastfeeding them reduces a woman's lifetime risk of developing breast cancer. Additionally, breastfed infants may have a lower risk of becoming obese and thus a reduced risk of cancer. It recommends that infants be exclusively breastfed for up to 6 months.
Dr. John Milner of NCI's Division of Cancer Prevention was an observer on the expert panel and chair of a working group that evaluated the scientific evidence for mechanisms by which dietary components may cause cancer. He notes that individual susceptibility to cancer from dietary causes varies widely because of genetic and other factors, but researchers don't yet know enough to craft dietary recommendations based on individual risk levels.
The report's dietary recommendations are consistent with current scientific knowledge and with dietary guidance promoted by the U.S. government through the Dietary Guidelines for Americans, the "Fruit and Veggies - More Matters" campaign (formerly "5 A Day for Better Health"), and other programs, Dr. Milner says.
The report recommends against consumption of dietary supplements to prevent cancer. Although some studies, usually in high-risk groups, have suggested that supplements can reduce cancer risk, these findings may not apply to the general population. The panel concludes that "the best source of nourishment is food and drinks."