Estimates suggest that approximately 35 per cent of cancers are a consequence of suboptimal diet. In this publication, epidemiologists, basic scientists and clinicians review both the epidemiology and mechanistic aspects of nutrition in the prevention of lung, breast, colorectal and prostate cancer. Moreover, an update on the status of the European EPIC study is given. Protein-calorie malnutrition of a clinically significant degree is common among cancer patients and contributes significantly to both morbidity and mortality: besides causing death solely from progressive cachexia, malnutrition leads to diminished cardiac performance, an increased susceptibility to infection and a diminished response to chemotherapy. Reversing, or even attenuating, this cachexia is an extremely problematic issue. The topics covered here include mechanisms by which malnutrition evolves in cancer patients, animal models of cancer wasting, and controversial nutritional interventions in cancer patients.