Implications of total energy intake for epidemiologic studies of breast and large-bowel cancer.

Animal studies suggest that the energy-restriction hypothesis should be considered in addition to the fat-composition hypothesis as an explanation for the strong international differences in risk of breast cancer. Because of the complex meaning of total energy intake, studies that attempt to examine directly the relationship between energy intake and cancer risk are likely to be misleading. Carefully conducted and interpreted studies of height and relative weight may be more revealing, although they are susceptible to diagnostic bias. These studies may prove useful in expanding our limited knowledge about breast and colon cancer, but they will have few direct implications for public health because individuals are not likely to restrict their energy intake voluntarily to a substantial degree, even if the energy-restriction hypothesis is correct.