Eat other foods from plant sources, such as breads, cereals, grain products, rice, pasta, or beans several times each day. Include grain products in every meal. Choose beans as an alternative to meat. The scientific basis for these recommendations is very strong for cancers at many sites, particularly for cancers of the gastrointestinal and respiratory tracts. The evidence is particularly strong that increased consumption of fruits and vegetables reduces the risk of colon cancer.
Evidence is less strong for cancers considered hormonal, such as breast and prostate.
The major risk factor for lung cancer is tobacco, but diet also affects risk. Studies have shown that people who smoke cigarettes tend to eat less healthful diets than nonsmokers, but fruits and vegetables reduce cancer risk whether or not people smoke. Because many studies indicate that foods high in beta carotene protect against lung cancer, scientists have suggested that beta carotene itself might reduce lung cancer risk. Recent clinical trials of beta carotene supplements, however, have shown that smokers taking the supplement developed lung cancer at higher rates than those taking a placebo. These findings support the idea that beta carotene may be a proxy for other protective nutrients or substances, singly or in combination, within foods.