[The significance of nutrition in primary prevention of cancer].

The complex process of carcinogenesis is mainly due to environmental factors and therefore preventable. Diet may account for about 35% of cancer cases; risk factors and protective factors are discussed. Accordingly, obesity is associated with an increased risk of endometrial and postmenopausal breast cancers. Less clear is the relationship with colorectal and prostate cancer. The observed inverse association of body weight with lung cancer risk is most probably confounded by smoking habits and/or the effect of preclinical cancer. The risk factor fat has been studied mainly in relation to colorectal, breast and prostate cancer; the results are controversial. More consistent are the associations between (red) meat consumption and risk of colorectal and prostate cancer. Alcohol is a risk factor for tumors of the upper gastrointestinal tract, the hepatocellular carcinoma and the (distal) colorectal cancer. Even small amounts of alcohol seem to increase the risk of breast cancer. Residues, contaminants, mycotoxins and additives like benzopyrene, nitrosamine(s), and aflatoxine are associated with a smaller risk of cancer than "overnutrition". High intake of fruit and vegetables is related to a reduced risk of lung cancer and cancer of the upper gastrointestinal tract. What the specific chemicals in fruits and vegetables are that are responsible for this association are still unclear. Despite only weak associations between dietary factors and cancer risk, for potential protective effects it is recommendable to increase the consumption of fruit and vegetables, to avoid obesity, to reduce the intake of fat, meat and alcohol and to avoid cured, pickled, smoked, and mouldy food.