This is because obesity raises blood levels of insulin and estrogen after menopause, both of which are known causes of breast cancer.
With regard to exercise, an association between physical activity and a reduced risk of breast cancer is unclear, although at least one study conducted by the Harvard School of Public Health showed that increased physical activity among post-menopausal women is associated with decreased risk of breast cancer.
The role of diet in breast cancer is also uncertain. In fact, the Nurses’ Health Study showed no relationship between breast cancer and high-fat diets. Researchers haven’t yet determined why Asian women have vastly lower risks of breast cancer, although some believe that the typical Asian diet, which is rich in plant estrogens called phytoestrogens, may protect against the destructive effects of human estrogen.
Other research suggests that breast cancer risk is higher for women whose mothers ate a high-fat diet, consumed alcohol or were under stress during pregnancy.