Obesity and breast cancer.

The high incidence of breast cancer in Western women has been linked to nutritional factors such as high-fat/low-fibre diet, obesity and timing of weight gain. A mechanism is postulated through which the Western diet could act in conjunction with inadequate exercise and excessive weight gain at the time of a major change in hormonal balance. All these factors favour the manifestation of insulin resistance, and the concomitants of hyperinsulinaemia might then synergise with oestrogen in promoting the development of breast cancer. The mechanism is compatible with the 'breast tissue age' model of mammary carcinogenesis. The concomitants of hyperinsulinaemia could also influence the growth of established disease subsequent to its promotion, and it is suggested that the hypothesis be tested by an adjuvant randomised trial of a high-fibre/low-fat diet in patients following primary surgery for early breast cancer. It has been suggested that the development of insulin resistance may link the Western lifestyle not only to an increased risk of hypertension and arteriosclerosis, but also to increased breast cancer risk. Large abdominal fat deposits in women are frequently a marker of the presence of insulin resistance and are generally associated with an increased level of bio-available oestrogen. There is evidence that predominantly abdominal distribution of fat in women may be a marker of increased breast cancer risk from puberty onwards. Abdominal obesity may however be hidden, and it is more reliably demonstrated by imaging techniques such as CAT or MRI scans, than by anthropometric measurements such as increased waist-to-hip ratio.