A dietary intervention study based on a randomised double-blind parallel design will be conducted in 30 pre-menopausal women (age 35-50) at moderate to high risk of developing breast cancer. The metabolomic profiles of urine and serum samples (collected at baseline and after dietary intervention) will be assessed. Participants will be randomised into two groups; the placebo group (consuming 6g of non-supplemented chocolate per day) and the supplemented group (consuming 6g of chocolate containing both soy and selenium per day). The intervention will last for the duration of one menstrual cycle.