Cancer Education Center

Common Questions About Diet & Cancer

Because people are interested in the relationship that specific foods, nutrients, or lifestyle factors have to specific cancers, research on health behaviors and cancer risk is often reported on the news. No one study, however, provides the last word on any subject, and single news reports may put too much emphasis on what appear to be contradictory or conflicting results. In brief news stories, reporters cannot always put new research findings in their proper context. Therefore, it is rarely, if ever, advisable to change diet or activity levels based on a single study or news report. The following questions and answers address common concerns about diet and physical activity in relation to cancer.

Alcohol

Does alcohol increase cancer risk?Yes. Alcohol raises the risk of cancers of the mouth, pharynx (throat), larynx (voice box), esophagus, liver, and breast, and probably of the colon and rectum. People who drink alcohol should limit their intake to no more than 2 drinks per day for men and 1 drink per day for women. A drink is defined as 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of 80-proof distilled spirits. The combination of alcohol and tobacco increases the risk of some cancers far more than the effect of either drinking or smoking alone. Regular intake of even a few drinks per week is linked to a higher risk of breast cancer in women, especially in women who do not get enough folate. Women at high risk of breast cancer may want to consider not drinking any alcohol.

Antioxidants

What are antioxidants, and what do they have to do with cancer?The body seems to use certain nutrients in vegetables and fruits to protect against damage to tissues that happens constantly as a result of normal metabolism (oxidation). Because such damage is linked with increased cancer risk, the so-called antioxidant nutrients are thought to protect against cancer. Antioxidants include vitamin C, vitamin E, carotenoids, and many other phytochemicals (chemicals from plants). Studies suggest that people who eat more vegetables and fruits, which are rich sources of antioxidants, may have a lower risk for some types of cancer. Clinical studies of antioxidant supplements are currently under way but have not yet proven to reduce cancer risk from vitamin or mineral supplements (also see entries for: beta-carotene, lycopene, vitamin E, supplements). To reduce cancer risk, the best advice at present is to get your antioxidants through food sources rather than supplements.

Fat

Will eating less fat lower cancer risk?There is little evidence that the total amount of fat a person eats affects cancer risk. But diets high in fat tend to be high in calories and may contribute to obesity, which in turn is linked with an increased risk of several types of cancer. There is evidence that certain types of fats, such as saturated fats, may increase cancer risk. There is little evidence that other types of fat (omega-3 fatty acids, found mainly in fish), monounsaturated fatty acids (found in olive and canola oils), or other polyunsaturated fats reduce cancer risk.

Obesity

Does being overweight increase cancer risk?Yes. Being overweight or obese is linked with an increased risk of cancers of the breast (among women after menopause), colon, endometrium, esophagus, kidney, and possibly other sites as well. Although research on whether losing weight reduces cancer risk is limited, some research suggests that weight loss does reduce the risk of breast cancer. Because of other proven health benefits, people who are overweight are encouraged to lose weight. Avoiding excessive weight gain in adulthood is important not only to reduce cancer risk but also to reduce the risk of other chronic diseases.

Fiber

What is dietary fiber, and can it prevent cancer?Dietary fiber includes a wide variety of plant carbohydrates that humans cannot digest. Specific categories of fiber are "soluble" (like oat bran) or "insoluble" (like wheat bran and cellulose). Soluble fiber helps to reduce blood cholesterol, which lowers the risk of coronary heart disease. Good sources of fiber are beans, vegetables, whole grains, and fruits. Links between fiber and cancer risk are weak, but eating these foods is still recommended. These foods contain other nutrients that may help reduce cancer risk and have other health benefits.

Genetics

If our genes determine cancer risk, how can diet help prevent cancer?Damage to the genes that control cell growth can be either inherited or acquired during life. Certain types of mutations or genetic damage can increase the risk of cancer. Nutrients in the diet can protect DNA from being damaged. Physical activity, weight control, and diet might delay or prevent the development of cancer in people with an increased genetic risk for cancer. The interaction between diet and genetic factors is an important and complex topic, and a great deal of research is under way in this area.

Physical activity

Will increasing physical activity lower cancer risk?Yes. People who engage in moderate to vigorous levels of physical activity are at a lower risk of developing colon and breast cancer than those who do not. Risk is lowered whether or not the activity affects the person's weight. Data for a direct effect on the risk of developing other cancers is more limited. Even so, obesity and being overweight have been linked to many types of cancer, and physical activity is a key factor in reaching or staying at a healthy body weight. In addition, physical activity has helpful effects against heart disease and diabetes.

Vegetables and fruits

Will eating vegetables and fruits lower cancer risk?In most of the studies looking at large groups of people, eating more vegetables and fruits has been linked to a lower risk of lung, oral, esophageal, stomach, and colon cancer. Because we don't know which of the many compounds in these foods are most helpful, the best advice is to eat 5 or more servings of an assortment of colorful vegetables and fruits each day. (This means at least 5 servings of fruits and vegetables when added together, for instance, 4 servings of vegetables plus 1 serving of fruit.)

What are cruciferous vegetables, and are they important in cancer prevention?Cruciferous vegetables belong to the cabbage family and include broccoli, cauliflower, Brussels sprouts, and kale. These vegetables contain certain compounds thought to reduce the risk for colorectal cancer. The best evidence suggests that eating a wide variety of vegetables, including cruciferous and other vegetables, reduces cancer risk.

Is there a difference in nutritional values among fresh, frozen, and canned vegetables and fruits?Yes, but they can all be good choices. Fresh foods are usually thought to have the most nutritional value. But frozen foods can often be more nutritious than fresh foods because they are often picked ripe and quickly frozen (whereas fresh foods may lose some of their nutrients in the time between harvesting and eating). Canning is more likely to reduce the heat-sensitive and water-soluble nutrients because of the high heat that must be used. Be aware that some fruits are packed in heavy syrup, and some canned vegetables are high in sodium (salt). Choose vegetables and fruits in a variety of forms, and pay attention to the label information.

Does cooking affect the nutritional value of vegetables?Boiling vegetables, especially for long periods, can leach out their content of water-soluble (B and C) vitamins. Microwaving and steaming are the best ways to preserve these nutrients in vegetables.