Dietary fat has been implicated in the development of hormone dependent breast cancer. Dietary fat has also been shown to increase the circulating reproductive hormones which are implicated in tumor growth and development. The interim dietary guidelines for cancer prevention recommend the reduction of dietary fat intake from 40% to 30% or even 20% of total colories. Most of the studies involving diet cancer - hormone relationship are epidemiological in nature or animal experimentations. We are proposing a study to investigate the circulating sex hormones: estrogens, progesterone, prolactin, sex hormone binding globulin and dehydroepiandro-stenedion sulphate, in a group of 24 health premenopausal women volunteers with serum cholesterol levels in the upper quartile. Two metabolic diets: AHA Phase 3 (20% calories from fat) and AHA Phase 2 (30% calories from fat) have been developed. These diets will be perpared in the Nutrition and Metabolism Research Laboratory. The volunteers will be consuming all the meals and snacks in the laboratory. A Standard American Diet will be fed to the women for one month and then AHA Phase 3 Diets (20% fat carlories) this year (Jan-June 1988) and AHA Phase 2 Diets (30% fat calories) next year (Jan-June 1989). The changes in circulating sex hormones as the women move from a high fat diet to a low fat diet will be examined. This project will aid in providing information on dietary fat - sex hormone association in normal healthy premenopausal women. Later this can be studied in women with cystic breast disease.