WESTERN DIET, EARLY PUBERTY, AND BREAST-CANCER RISK

The typical high fat, low fibre diet of the industrialised West, parti cularly when associated with inadequate exercise, is likely to advance the onset of puberty. This will manifest in girls as an earlier menar che, earlier onset of breast development, and an earlier growth spurt. Both earlier menarche and adult tallness are markers of increased ris k to breast cancer. Earlier menarche in the West is usually associated with earlier onset of hyperinsulinaemia, and multiple case-control st udies report that hyperinsulinaemia too is a marker of increased breas t cancer risk. Although the Western diet is linked both to earlier men arche and also to earlier hyperinsulinaemia, the mechanism involved is not necessarily the same. While menarche is likely to be triggered by a threshold level of fatness, manifestation of insulin resistance is genetically-determined and strongly influenced by the fatty acid profi le of the diet. The putative mechanisms by which they influence mammar y carcinogenesis also differ. Early menarche is reported to be associa ted with a raised oestradiol level persisting into early adult life. O n the other hand, hyperinsulinaemia is commonly associated with abnorm al aromatase activity in the ovaries. In addition, the concomitant inc rease in bioactive levels of insulin-like growth factor-I may synergis e with oestrogen in stimulating proliferative activity in mammary epit helium. Dietary modification and exercise regimens are proposed in fam ilies at high risk to breast cancer. The measures have been shown to r educe insulin levels in both children and adults, and serial monitorin g of insulin and sex steroid levels could be used to detect a metaboli c-endocrine effect.