Diet and breast cancer: studies in laboratory animals.

Increasing dietary fat content increases mammary gland tumorigenesis in laboratory rodents. The effect can be attributed only in part to increasing energy intake, which itself increases tumorigenesis. Restriction of dietary or energy intake, sufficient to reduce body weight, reduces mammary gland tumorigenesis. Consideration of these effects has led to discussion of the possible need for changes in the feeding of laboratory rodents in carcinogenesis bioassays and other chronic studies. Studies of endocrine or other growth factors for the mammary gland have not identified specific effects of dietary fat or energy. In addition, tumorigenesis in other organs responds similarly to increased fat or decreased energy intake, indicating that the mechanisms are not, or not entirely, specific for the mammary gland. Extrapolations of results between species must always be made with caution, but the marked effects of dietary fat and energy in rodent tumorigenesis models must be considered in designing diet advice for humans.