The Women's intervention Nutrition Study (WINS) is a prospective, randomized, multi-center clinical trial testing the hupothesis that dietary fat intake reduction as an adjuvant ti standard breast cancer therapy will reduce disease recurrence and increase survival for women with localized breast cancer. The hypothesis is based on strong epidemiological observations and plausible mediating mechanisms of action which include dietary fat influence on: circulating steroid hormones, prostaglandin synthesis, immune function, regulatory gene expression, and cancer cell membrane structure and function. Women (>48 to 78 vears of age) with a histologic diagnosis of localized breast cancer not already consuming a low-fat diet are potentially eligible. Following appropriate primary therapy surgery +/- radiation), all patients receive defined systemic adjuvant therapy (including tamoxifen, AC, CMF, FAC). Patients are randomly assigned to one of two Dietary Groups as the sole treatment variable; either Intensive Intervention (IIG) or Non- Intensive Intervention (NIG) Groups. The IIG receive individualized and group programs to reduce dietary fat intake to 15% of calories. The NIG are instructed in the current U.S. Dietary Guidelines (30% of calories from fat). Patients in both Dietary Groups are counselled regarding the dietary adequacy for RDA nutrients. Dietary fat intake is estimated with serial, unannounced food recalls. Weight change and, in a subset-serum, fatty acid concentration profiles assess dietary adherence. All patients are followed for disease-free survival (as primary study endpoint) and overall survival. This multi- disciplinary, multi-center trial includes an Administrative Unit, an External Advisory Committee, a Nutritional Coordinating Unit, a Statistical Coordinating Unit, two Regional nutrition Centers and over 30 participating Clinical Sites Quality control policies and procedures are in place and operative. The initial two years funding of the WINS outcome Trial has demonstrated an ability to maintain a sustained rate of breast cancer patient accrual with associated dietary adherence sufficient to definitively address the study hypothesis. The successful completion of this study will provide a definitive evaluation of the effect of dietary fat intake reduction on breast cancer patient outcome.