The major risk factors for breast cancer are hormone-related, and the only well-established diet-related risk factors for breast cancer are obesity and alcohol consumption. Obesity increases breast cancer risk in postmenopausal women by around 30%, probably by increasing serum concentrations of bioavailable oestradiol. Moderate alcohol intakes increase breast cancer risk by about 7% per alcoholic drink per day, perhaps also by increasing oestrogen levels. Populations with high fat intakes generally have high rates of breast cancer, but studies of individual women have not confirmed an association of high fat diets with breast cancer risk. Phyto-oestrogens can affect hormone metabolism, but data on phyto-oestrogen consumption and breast cancer risk are inconsistent. Nutrition might affect breast cancer risk by altering levels of growth factors such as insulin-like growth factor-I. Current dietary advice should be to avoid obesity, limit alcohol intake, and maintain a varied diet.