AbstractThe literature is reviewed for evidence concerning the relation between caloric intake, body weight, and cancer. Convincing experimental data regarding caloric intake and benign and malignant tumor incidence have been available since the 1940s and demonstrate that caloric restriction significantly reduces tumor incidence for a variety of tumor types in several animal models. Some epidemiological investigations provide evidence for a positive calorie‐cancer association in humans, although it is difficult (in these studies) to separate the effects of calories per se from those of dietary fat. A larger number of investigations have evaluated body weight alone, and high relative body weight or high caloric intake has been associated with increased risk of cancer of the breast, colon, rectum, prostate, endometrium, kidney, cervix, ovary, thyroid, and gallbladder. In contrast, lung, bladder, and stomach cancers appear to be inversely associated with body weight, and some prospective studies of men demonstrate greater total cancer mortality among lean individuals. However, in their analyses, few of these latter investigations considered the effects of cigarette smoking, antecedent illness, or competing causes of death. While the relations between caloric intake, other dietary macronutrients (e.g., fat), and body weight are complex and require further investigation, a complete review of the data suggests that reducing caloric intake and relative body weight may lead to a considerable decrease in cancer risk in humans.