Author's recommendations are not justified

EDITOR—The epidemiological literature justifies only two of the conclusions that Cummings and Bingham draw in their review about diet and the prevention of cancer: the recommendations to avoid (high doses of) vitamin supplements and mouldy foods.1 Even the cited report of the World Cancer Research Fund shows that the overall evidence for dietary recommendations is weak if one takes into account the more reliable data from prospective cohort and intervention studies.2

Cummings and Bingham give an excellent example of publication bias in their section on colorectal cancer and red meat: they cite two prospective studies that support a role for red meat in colorectal carcinogenesis. What they do not mention is that—beside at least three other studies—five prospective studies cited in the World Cancer Research Fund's report did not find a significant association with red meat.

It is not yet proved that heterocyclic amines or N-nitroso compounds definitely increase rates of colon cancer.3 Bingham herself has shown that the endogenous production of N-nitroso compounds varies widely between individuals and also depends on other components of the diet (for example, resistant starch).4 Recent research has shown that chicken, which is often recommended as a healthy substitute for red meat, can contribute heavily to the uptake of heterocyclic amines.5

Cummings and Bingham's statement that “non-starch polysaccharides (fibre) and vegetables are established factors that reduce risk” is also misleading. As is shown in the World Cancer Research Fund's report, none of four prospective cohort studies on non-starch polysaccharides showed a significant reducing effect on colon or rectal cancer.

The protective effect of vegetables is also far from proved. Of four prospective cohort studies cited in the World Cancer Research Fund's report, one found no effect with green salad; one found a significant reduction in risk with …