The trial is explanatory in that it seeks to determine if there is a biological effect of dietary fat reduction in terms of a reduction in breast cancer incidence. To meet this goal we will select as participants highly motivated subjects who are at increased risk of breast cancer, provide them with a high level of assistance in making a dietary alteration, follow them carefully to ensure the correct identification of subjects who develop breast cancer, and analyse the results both according to intention to treat and dietary compliance. This trial does not attempt to assess directly the possible effects of dietary counselling on the health of the general public.