High-meat diets and cancer risk

Up to 80% of breast, bowel and prostate cancers are attributed to dietary p ractices, and international comparisons show strong positive associations w ith meat consumption. Estimates of relative risk obtained from cohort inves tigations are in the same direction, although generally weak, and red and p rocessed meats rather than white meat seem to be associated with elevated r isk of colon cancer. In breast cancer, there are consistent associations wi th total meat intake and there is evidence of a dose response. Despite thes e associations with meat, existing studies suggest that vegetarians do not have reduced risk of breast, bowel or prostate cancer, but there are no qua ntitative estimates of amounts of meat consumed by meat eaters in these coh ort studies. Possible mechanisms underlying epidemiological associations in clude the formation of heterocyclic amines in meat when it is cooked. These heterocyclic amines require acetylation by P450 enzymes, and individuals w ith the fast-acetylating genotype who eat high amounts of meat may be at in creased risk of large-bowel cancer. NH3 and N-nitroso compounds (NOC) forme d from residues by bacteria in the large bowel are probably also important. NH3 is a promotor of large-bowel tumours chemically induced by NOC, and so me of the chromosomal mutations found in human cole-rectal cancer are consi stent with effects of NOC and heterocyclic amines. However, the type, amoun t, and cooking method of meat or protein associated with increased risk are not certain. The effects of high levels of meat on NH3 and NOC output are not reduced by increasing the amount of fermentable carbohydrate in the die t, but interaction between meat, NSP and vegetable intakes on the risk of c ancer has not been studied comprehensively. The interaction between dietary low-penetrance genetic polymorphic and somatic mutation factors has also b een investigated to a limited extent. Current Department of Health (1998) r ecommendations are that meat consumption should not rise, and that consumer s at the top end of the distribution should consider a reduction in intakes .