This hypothesis is consistent with the high incidence of esophageal cancer in several areas with impoverished agriculture and poor diet. The results suggest that the influence of vegetables and fruits on stomach cancer is not simply attributable to vitamin C, as most people would have said 5 years ago. Raw vegetables are not particularly high in vitamin C, nor are non-citrus fresh fruits. These vegetables and fruits have a protective effect, and we do not know what the active entities are. Thus, although the evidence for a protective role for carotenoids, vegetables, and fruits is most persuasive for lung cancer, increased vegetable and fruit intake also decreases risk for other cancers, specifically cancers of the mouth, larynx, pharynx, esophagus, stomach, colon, rectum, pancreas, and bladder.
Results are mixed for the hormone-related cancers.
Although total vegetable and fruit intake does not have a role in prostate cancer, Dr. Giovannucci will be presenting new findings for lycopene later this morning. Research on diet and the lymphatic and hemopoietic cancers is limited. It is important to emphasize that different mechanisms whereby carotenoid-rich vegetables and fruits are protective exist for the different cancer sites, and there may well be a variety of critical factors. This guidance is based on the numerous studies that show protective effects of vegetables and fruits for many, though not all, cancers. More than 200 epidemiologic studies have yielded persuasive results with a variety of assessment methods, designs, and analytic approaches.