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What is the role of diet in cancer?

It is increasingly clear that diet can play a major role in the prevention of cancer. According to the National Cancer Institute, 35 percent of the all cancer deaths in the United States are directly related to diet. Recent population studies indicate that more than 150,000 cancer deaths could be prevented in the United States each year by two relatively simple dietary changes:

• Cutting fat consumption
  to 20 percent of total calories, just over half of the present average intake.
• Doubling the average intake of dietary fiber to 20 to 30 grams a day.
  

Specific diet-cancer associations include:

• Cancers of the prostate, breast, colon, ovaries are linked to a high-fat diet.
• Cancers of the liver, mouth, throat, and esophagus are linked to excessive alcohol.
• Cancers of the stomach and esophagus are linked to a high intake of smoked, salted, and pickled foods.

Recent research also indicates that certain vitamins and other food chemicals protect against cancer. For example, foods high in antioxidant nutrients—especially beta carotene and vitamins A, C, and E—protect against the cellular damage from oxygen metabolism that promotes cancer. Broccoli, Brussels sprouts, cauliflower, and other related vegetables contain flavonoids, indoles, and other chemicals that inhibit tumor growth. The sulfur compounds in garlic also block some cancer-causing agents and inhibit tumor growth.

Diet is also a critical aspect of cancer treatment. Although there is no dietary cure for cancer, patients with good nutritional status are better able to withstand the rigors of surgery, chemotherapy, and other treatments. Special nutritional therapy, including high-calorie supplements and tube feeding, may be recommended to help maintain weight and nutritional status, especially for people who are unable to eat normally.

What can I do myself?

In addition to adopting a high-fiber, low-fat diet, experts in cancer prevention recommend the following preventive measures:

Maintain ideal weight. People who are obese, defined as 20 percent above ideal weight, have an increased incidence of colon, breast, prostate, gallbladder, ovarian, and uterine cancers.

Eat a variety of fruits and vegetables. The Food Pyramid calls for 5 to 9 servings a day, with special emphasis on dark green or deep yellow fruits and vegetables, which are high in vitamin C and beta-carotene. Have 3 or more servings of broccoli, cabbage, and other cruciferous vegetables each week.

Cut down on meat. Not only is meat high in saturated fats, but it also may harbor hormones and other chemicals that are thought to promote cancer. Substitute pasta, legumes, and other vegetarian dishes for at least some servings of meat. And when you do eat meat, choose lean cuts.

Limit alcohol consumption. This is especially important if you smoke cigarettes or use other tobacco products such as snuff.

Limit intake of cured foods. Avoid especially those that are smoked or cured with nitrites.

If you are undergoing cancer treatment, make every effort to eat enough to maintain normal weight. This is often difficult because the cancer itself causes weight loss and may alter taste or reduce appetite. In addition, cancer treatment may cause nausea, loss of appetite, mouth sores, diarrhea, and other side effects that make eating difficult. Special nutritional supplements can help counter these problems.

Avoid fad diets, such as a strict macrobiotic regimen, that are often promoted as a cancer treatment by practitioners of alternative medicine. Such diets tend to be low in calories and fail to provide essential nutrients.

When should I see my doctor?
Unexplained weight loss warrants prompt medical investigation. If you are

undergoing cancer treatment, you may be referred to an oncology nurse or dietitian experienced in working with cancer patients. Many treatment side effects can be countered by dietary changes. For example, a diet low in fat, fiber, and gluten (a protein in wheat and other grains) can help control diarrhea related to chemotherapy or radiation treatments. However, expert help is needed to structure a diet that provides adequate nutrition.

You should also consult a doctor or registered dietitian for nutrition-related problems that increase the risk of cancer. For example, if you are overweight and have difficulty maintaining weight loss, seek professional help to overcome the faulty eating habits that contribute to obesity. A dietitian can also show you how to develop menus that follow the American Cancer Society guidelines for a preventive diet.

What will the doctor do?
In general, all patients undergoing chemotherapy, radiation treatments, or other lengthy, debilitating therapy should be referred to a dietitian or other health professional experienced in nutritional assessment and counseling.

For patients who are unable to eat or consume adequate calories, tube feeding (parenteral and enteral nutrition) may be recommended to maintain nutritional status. Tube feeding is often administered in the hospital, but for patients who are well enough to be treated at home, it can be provided by a visiting nurse or a family member who has been trained in the procedure.

Long-term approach

Moderation and common sense should govern your long-term approach to diet and cancer. Be wary of diets that are promoted as cancer cures or preventatives. Instead, maintain normal weight and consume a prudent, balanced diet that follows the Food Pyramid.

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