Diet and cancer.

Accumulating data indicate that modifications in diet may reduce the risk of cancer by as much as one third and possibly by as much as two thirds. On the basis of the existing evidence, however, it is not possible to be certain which cancers are causally related to diet and what proportion of them are due to specific components of the diet. Diet is currently thought to be a major factor in the aetiology of cancers of the large bowel and stomach, and it may also be important in the aetiology of several other cancers. With the exception of strong and consistent evidence of the protective effect of fruit and vegetables, practical dietary interventions that reduce the risk of cancer are difficult to formulate as, in general, the evidence is theoretical or contradictory and too weak to justify specific intervention. Authoritative guidelines on dietary management in primary care are conspicuously absent because of lack of research. The success of an individual based strategy will depend on adequate education, training, and support being made available to the relevant members of primary care teams. Most of the evidence on diet and cancer is as yet inconclusive. There is, however, accumulating data indicating that modifications in diet may reduce the risk of cancer by as much as one third and possibly by as much as two thirds. That diet can influence the incidence of cancer is abundantly clear from experimental studies in animals, which have shown that it can do so in many different ways, not only by introducing into the body carcinogens or substances from which carcinogens are formed in vivo but also by affecting the metabolism of carcinogens and the body's reaction to them. International comparisons between patterns of food consumption in different populations and the incidence of cancers in these …