Cancer Risk Increased by Excess Body Fat, Red and Processed Meats, and Alcohol

Roxanne Nelson

October 31, 2007 — There is convincing evidence that excess weight and obesity can increase the risk for 6 different cancers, including those of the colon, kidney, and pancreas, according to a report issued by the American Institute for Cancer Research (AICR) and the World Cancer Research Fund. The second expert report, Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective, considered to be the most comprehensive scientific analysis of cancer prevention and causation ever undertaken, also reported that there is convincing evidence that the consumption of alcohol, red meat, and processed meat elevates cancer risk.
"The most striking finding in the report is that excess body fat increases risk for numerous cancers. That is why body weight is the focus of our first recommendation," expert panel member W. Phillip T. James, MD, DSc, from the International Obesity Task Force, in London, United Kingdom, told journalists.
The document, which was written by an international expert panel, reviewed 7000 research studies over a 5-year period and classified the accumulated evidence for specific diet-cancer links. It is the second one to be published in the past 10 years and provides the most inclusive evidence to date linking cancer risk to diet, physical activity, and weight.
Although cancer is considered to be a disease of genes that are vulnerable to mutation, evidence indicates that only a small number of cancers are inherited, write the experts. Instead, it appears that environmental factors are the most important, and these can often be modified with a resultant reduction in risk. These factors include tobacco use, infectious agents, radiation, industrial chemicals, pollution, medications, nutrition, physical activity, and body composition.
One of the strongest findings in the report was that excess body fat is associated with an increased cancer risk and can increase the risk for 6 different types of the disease: colon, kidney, pancreas, adenocarcinoma of the esophagus and endometrium, and postmenopausal breast cancer. They also reported that alcohol is convincingly linked to a number of cancers, including those of the colon, breast, esophagus, and mouth, larynx and pharynx.
To combat excess weight and maintain a healthy body-mass index, the experts recommend limiting the intake of energy-dense foods, particularly those that are highly processed. These products tend to be high in sugar and fat and low in fiber. They also advise increasing physical activity and getting some exercise for at least 30 minutes a day. Physical activity not only helps individuals keep excess weight off, but it helps reduce the risk for cancer in its own right.
Evidence has also increased since the first report, issued in 1997, which links the consumption of red meat (beef, pork, and lamb) to colorectal cancer. The panel's recommendation is to limit the consumption of red meat to 18 ounces per week because, beyond this amount, evidence shows that for every additional 1.7 ounces of red meat consumed per day, the risk for cancer rises by 15%.
Their recommendation concerning the consumption of processed meats is even more stringent. Processed meats, such as bacon, ham, sausage, and lunch meat, should be avoided entirely; the panel was unable to find a level at which the consumption of these products can be reliably considered completely safe. For every 1.7 ounces of processed meat consumed per day, the risk for colorectal cancer rises by 21%.
Evidence also indicates that the majority of diets that are protective against cancer are made up primarily of foods of plant origin. Higher consumption of several plant foods might offer protection against cancers of various sites.
"We are recommending 5 servings or more of vegetables and fruit daily because, like physical activity, they pack a double whammy against cancer. Probable evidence indicates that they help reduce cancer risk on their own and, as low energy-dense foods, they help maintain a healthy weight, which the evidence shows has a big influence on cancer risk," Dr. James said during a press conference.
The panel also looked at factors that included birth weight, childbearing, breast-feeding, and adult height and found that they all can influence the risk for cancer. High birth weight is associated with an increased risk for premenopausal breast cancer, which is likely linked to excess body fat and the resultant hormonal changes.
Exclusive breast-feeding appears to offer protection for both mother and child. It can help lower the risk for breast cancer in women and also lower the risk of becoming overweight and obese in children.
"The evidence is uniformly strong on breast-feeding, and the fact that it offers cancer protection to both mothers and their children is why we made breast-feeding 1 of our 10 recommendations to prevent cancer," said expert panel member Walter J. Willett, MD, PhD, from the Harvard School of Public Health, in Boston, Massachusetts, at a press conference.
The panel also found an association between adult height and cancer risk. Tall adults appear to have a higher risk of colorectal and postmenopausal breast cancer, and there is some evidence linking tallness to an increased risk for ovarian, pancreatic, and premenopausal cancer.
The recommendations made in this report are applicable to cancer survivors when appropriate and unless otherwise advised by their healthcare practitioner. Because increasing numbers of cancer patients survive their disease and live long enough to develop new primary cancers or other chronic diseases, the expert panel believes that these recommendations can help reduce the risk.
Recommendations for Cancer Prevention
1. Be as lean as possible within the normal range of body weight.2. Be physically active as part of everyday life.3. Limit consumption of energy-dense foods; avoid sugary drinks.4. Eat mostly foods of plant origin.5. Limit intake of red meat; avoid processed meat.6. Limit alcoholic drinks.7. Limit consumption of salt; avoid moldy cereals (grains) or pulses (legumes).8. Aim to meet nutritional needs through diet alone.
Special Population Recommendations
9. Mothers should breast-feed; children should be breast-fed.10. Cancer survivors should follow the recommendations for cancer prevention.
World Cancer Research Fund/American Institute for Cancer Research. Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective. Washington, DC: AICR; 2007.