Experts believe that more than half of human cancers may be preventable. Diet, as well as tobacco use, infections, and chemicals or hormones are thought to be major risk factors that can be changed. However, there is still little agreement over which dietary changes can prevent most cancers.

Fiber and cancer; Cancer and fiber; Nitrates and cancer; Cancer and nitrates

DIET AND CERTAIN CANCERS

Diet and breast cancer: Although a high-fat diet has been studied as a cause of breast cancer, no clear evidence has been found. A high-fat diet may promote breast cancer by causing the body to release more of certain hormones.

Det and prostate cancer: Because prostate cancer appears to be more common with a Western lifestyle, diet has been closely studied as a risk. However, results have not led to a clear answer:

• Fats. Some studies have linked prostate cancer to a high-fat diet, especially including red meat and high-fat dairy products.
• Vegetables and fruits. A diet rich in vegetables, fruits, and legumes appears to protect against prostate cancer. This may be because these foods are low in fat. No one vegetable or fruit has been proven to decrease the risk. Lycopene, which is found in tomatoes, has been investigated, but the evidence that it protects against prostate cancer has not been proven.
• Vitamins and minerals. Major studies have found that vitamin and mineral supplements (vitamin E, vitamin C, vitamin D, and selenium) do not prevent prostate cancer.
• Calcium. A high intake of calcium has been linked to an increased risk for prostate cancer in some studies.

Diet and colon or rectal cancer:

• A diet high in red and processed meats increases the risk for colorectal cancer. Diets high in fruits and vegetables appear to reduce the risk.
• Several major studies have found that eating a lot of high-fiber foods protects against colorectal cancer, but other studies show little benefit.
• It is also not clear whether a lack of certain vitamins, such as folic acid (a type of B vitamin), could increase the risk for colorectal cancer. Recent studies have shown that taking folic acid supplements does not lower the risk of getting colorectal cancer, and that supplements appear to increase the risk for polyps.

Diet and stomach or esophageal cancer: Countries in which people eat a lot of salt-cured, smoked, and nitrite-cured foods have a high rate of cancer of the stomach and esophagus. Examples of such foods include bacon, ham, hot dogs, and salt-cured fish.

RECOMMENDATIONS

The best advice is to eat a well-balanced diet and avoid focusing on one "cancer-fighting" food.

• Choose foods and portion sizes that promote a healthy weight.
• Choose whole grains instead of refined grain products to increase fiber in the diet (25 to 35 grams of fiber per day).
• Eat 5 or more servings of fruits and vegetables each day.
• Limit processed and red meat in your diet. Only eat salted, smoked, or cured foods on occasion.
• Limit alcohol to one drink per day (women who are at high risk for breast cancer should consider not drinking alcohol at all).
• Choose lean cuts of beef, lamb, and pork, as well as skinless poultry and fish. Baking, broiling, poaching, and steaming are the best cooking methods. Choose skim or low-fat milk and dairy products, as well as low-fat salad dressings.

RESOURCES:

• Dietary Guidelines for Americans
• The American Cancer Society is an excellent source of information on cancer prevention. www.cancer.org
• The American Dietetic Association provides sound dietary advice on a wide range of topics. www.eatright.org
• The National Cancer Institute's CancerNet is a government gateway to the latest, most accurate information on cancer prevention. www.cancer.gov

United States Department of Agriculture. Center for Nutrition Policy and Promotion. Dietary Guidelines for Americans. 2010. National Academy Press, Washington, DC, 2010.

Pierce JP, Natarajan L, Caan BJ, Parker BA, Greenberg, Flatt SW, et al. Influence of a diet very high in vegetables, fruit, and fiber and low in fat on prognosis following treatment for breast cancer: the Women's Healthy Eating and Living (WHEL) randomized trial. JAMA. 2007;293;289-298.

A Dahm CC, Keogh RH, Spencer EA, Greenwood DC, Key TJ, Fentiman IS, et al. Dietary fiber and colorectal cancer risk: a nested case-control study using food diaries. J Natl Cancer Inst. 2010;102:614-626.

Larsson SC, Orsini N, Wolk A. Vitamin B6 and risk of colorectal cancer: a meta-analysis of prospective studies. JAMA. 2010;303:1077-1083.

Gaziano JM, Glynn RJ, Christen WG, Kurth T, Belanger C, MacFadyen J, et al. Vitamins E and C in the prevention of prostate and total cancer in men: the Physicians' Health Study II randomized controlled trial. JAMA. 2009;301:52-62.

Kushi LH, et al. American Cancer Society guidelines on nutrition and physical activity for cancer prevention: reducing the risk of cancer with healthy food choices and physical activity. CA Cancer J Clin. 2006;56:254-281.

Zell JA, Meyskens FL. Cancer prevention, screening, and early detection. In: Abeloff MD, Armitage JO, Niederhuber JE, et al. Abeloff's Clinical Oncology. 4th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2008:chap 26.