Diet and colorectal cancer prevention

The majority of cancers are sporadic and epidemiological estimates suggest that up to 80% of colorectal cancer is attributable to diet. Epidemiologica lly, cross-sectional comparisons, case-control studies and trends in food i ntake show high rates of colorectal cancer in populations consuming diets h igh in meat: and fat, and low in starch, NSP (non-starch polysaccharides, f ibre) and vegetables. In general, prospective studies tend to support these findings although estimates of relative risk are not high. Existing prospe ctive studies have however used crude indices of diet subject to substantia l measurement error, and interactions with genetic polymorphisms in, for ex ample, phase-I and -II enzymes have been studied only rarely. The associati on between meat consumption and colorectal cancer is usually attributed to the formation of heterocyclic amines in meat when it is cooked. In addition , in humans high-meat diets increase the level of nitrosatable material ent ering the colon so that faecal N-nitroso compounds (NOCs) increase in a dos e-responsive manner following endogenous synthesis in the colon. Some of th e mutations and guanine adducts accumulated during colorectal cancer progre ssion are characteristic of alkylative damage, which would be compatible wi th NOC exposure. To date, NSP, resistant starch and vegetables have not red uced faecal NOC levels.