The role of diet in breast cancer has been considered since the 1940s. However, most epidemiological studies on the incidence of the disease have been limited by their focus on one dietary component-fat-at the expense of a balanced consideration of the effect of the total diet. Further, only the intercultural comparison studies examine a wide range of fat intakes. These studies indicate a dearth of breast cancer in populations with diets in which less than 10% of calories are from fat. Although dietary fat, estrogenic food additives, and alcohol increase the risk of breast cancer, fiber, indoles, flavonols, vitamins C and E, beta carotene, and selenium are associated with a decreased risk. Except for alcohol, factors that increase risk predominate in animal products, whereas those that decrease risk abound in plant products. These factors have similar effects on progression and prognosis in breast cancer. Mechanistically, higher serum levels of estrogen have been linked with risk of breast cancer. Dietary fat, insecticide residues, and alcohol result in higher estrogen activity. A variety of plant nutrients have estrogen-blocking activity. Current evidence justifies recommending that women of all ages follow a plant-based diet in which fat provides no more than 10% of calories, with the goals of preventing breast cancer and improving its prognosis in a low-cost, safe manner.