Nutrition Notes
Week of April 16, 2007

Weight: Can You Change Its Impact on Your Risk of Cancer?

Karen Collins, MS, RD, CDN
American Institute for Cancer Research 

Since most adult cancers develop over 10 to 20 or more years, some overweight people may wonder if it’s too late for them to change their risk. Fortunately, recent research showing how body fat influences cancer risk suggests that we can change long-term negative health effects of excess weight.

Studies suggest that reducing excess body fat may lower cancer risk. In the Nurses’ Health Study, which followed more than 87,000 women for up to 24 years, post-menopausal women who lost 22 pounds or more and kept it off showed a 30 percent lower breast cancer risk than post-menopausal women who maintained their weight. Another major study, the Iowa Women’s Health Study, followed more than 33,000 women up to 15 years. Women who lost weight after menopause developed 23 percent less breast cancer compared to women who gained weight throughout adulthood. Women who began to lose weight before menopause reduced their risk even more. Among almost 70,000 men in the Cancer Prevention Study II, those who lost at least 11 pounds over a ten-year period faced 16 to 17 percent lower risk of prostate cancer, and 42 percent lower risk of aggressive forms of prostate cancer.

Our weight reflects the balance between calories we consume and calories we burn. Some studies suggest that it’s not just extra body fat that poses cancer risk, but the consequences of excess calories. This could mean that a few small changes could immediately begin reducing your cancer risk: eat less high-calorie food and more low-calorie vegetables, fruits and whole grains, and become a little more active. These changes will show up slowly in your weight.

Research suggests that regular physical activity reduces cancer risk regardless of weight. Studies show that after controlling for weight, regular moderate exercise may reduce risk of breast cancer 7 to 18 percent. Colon cancer risk drops 40 to 50 percent with exercise. Exercise may independently lower risk of prostate, lung, endometrial, ovarian and kidney cancers, although confirming studies are needed.

Researchers have identified three major ways that excess weight increases cancer risk. One comes from excess body fat secreting substances that seem to promote inflammation throughout the body, increasing the chance of DNA damage that allows cancer to start. The second, being overweight, can also lead to higher blood levels of insulin and insulin-related growth factors, which promote the development of some cancers. Third, excess body fat also changes levels of several reproductive hormones such as estrogen and testosterone.

Weight loss is a vital goal if you are overweight. But while weight loss is still “in progress,” or if your weight doesn’t end up as low as you wish, lifestyle choices that affect insulin and reproductive hormones might help modify weight’s risks. Limiting alcohol curbs its ability to raise estrogen levels; and eating plenty of dark green vegetables, whole grains and beans provides folate that may help counterbalance some of alcohol’s risks. Results haven’t been consistent, but some studies suggest that a high-fiber, low-fat diet may offer a double-whammy effect by fighting insulin resistance and lowering estrogen levels, especially among those who are overweight. A diet filled with vegetables, fruits and whole grains supplies antioxidants that may reduce some of the damage produced by excess body fat.

There is a bonus: These changes that may help reduce the risk that comes from excess weight are precisely the lifestyle changes that can also help you lose that weight.

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AICR’s Nutrition Hotline is a free service that allows you to ask a registered dietitian questions about diet, nutrition and cancer.  Access it online at www.aicr.org/hotline or by phone (1-800-843-8114) 9 a.m. to 5 p.m. ET Monday-Friday.  AICR is the only major cancer charity focused exclusively on the link between diet, nutrition and cancer. It provides education programs that help Americans learn to make changes for lower cancer risk. AICR also supports innovative research in cancer prevention and treatment at universities, hospitals and research centers.  It has provided more than $78 million for research in diet, nutrition and cancer.  AICR’s Web address is www.aicr.org.