Can vegetables prevent cancer?

The National Cancer Institute, in its booklet Diet, Nutrition, & Cancer Prevention: A Guide to Food Choices, states that 35 percent of cancer deaths may be related to diet. The booklet states:

• Diets rich in beta-carotene (the plant form of vitamin A) and vitamin C may reduce the risk of certain cancers.
• Reducing fat in the diet may reduce cancer risk and, in helping weight control, may reduce the risk of heart attacks and strokes.
• Diets high in fiber-rich foods may reduce the risk of cancers of the colon and rectum.
• Vegetables from the cabbage family (cruciferous vegetables) may reduce the risk of colon cancer.

FDA, in fact, authorized several health claims on food labels relating low-fat diets high in some plant-derived foods with a possibly reduced risk of cancer.

While FDA acknowledges that high intakes of fruits and vegetables rich in beta-carotene or vitamin C have been associated with reduced cancer risk, it believes the data are not sufficiently convincing that either nutrient by itself is responsible for the association. Nevertheless, since most fruits and vegetables are low-fat foods and may contain vitamin A (as beta-carotene) and vitamin C, the agency authorized a health claim relating diets low in fat and rich in these foods to a possibly reduced risk of some cancers.

Another claim relates low-fat diets high in fiber-containing vegetables, fruits and grains to a possible reduction in cancer risk. (The National Cancer Institute recommends 20 to 30 grams of fiber a day.) Although the exact role of total dietary fiber, fiber components, and other nutrients and substances in these foods is not fully understood, many studies have shown such diets to be associated with reduced risk of some cancers.