Review of the incidence of gastrointestinal neoplasms in Israel reveals that gastric and colorectal cancers present a major problem in the country. Diet has been postulated as a possible etiologic factor on the basis of a) an indirect correlation between disease incidence and the consumption of various food constituents, b) animal experimentation, and c) case-control dietary studies. Studies conducted in Israel point to high starch consumption as a risk factor in gastric cancer and low fiber intake as a risk factor in colon cancer. Mechanisms by which fiber may exert its protective effect include shortening of intestinal transit time, bulkier stool, lowered absorption of potential carcinogens, reduction of the conversion of bile salts to potentially carcinogenic sterols, interference with the cholesterol pool and a lower ratio of anaerobic:aerobic bacteria in the intestinal flora. The potential effect of excessive starch consumption is unclear, although it may facilitate the formation of nitrosamines.