The association between dietary fat consumption and risk of cancer, especially colon, breast, prostate, and ovary cancer, has been debated for many years. Ecologic studies over the past 30 years have demonstrated the correlation of greater dietary fat intake with higher mortality due to various cancers. Migrant studies also have shown that increased fat consumption may be associated with increased risk of cancer. Specific saturated fatty acids raise blood cholesterol levels and, thereby, increase the risk of atherosclerosis. Greater fat, intake is a major cause of obesity and hypertension, diabetes, and gallbladder disease. Higher fat intake may heighten the risk of breast cancer directly through increased blood estrogen levels and/or secondarily through increased obesity. The critical experimental studies to determine the effects of a low-fat diet on disease risk have not been completed, but reducing fat in the US diet has the potential to decrease morbidity and mortality substantially.