To review the current literature on the effects of soy isoflavones, one class of phyto-oestrogens, on cardiovascular diseases, osteoporosis, cancer and climacteric symptoms.

Many study designs were employed in the reports reviewed here, including prospective human trials, observational human studies, animal experiments and in vitro cell studies that explored the protective or preventive effects of soy isoflavones (genistein, daidzein and glycitein alone or mixed).

Diverse settings were employed, depending on study design.

Human subjects, mostly menopausal or postmenopausal, were included, as were animal models and specific cell types.

The findings were: (i) isoflavones plus soy protein together were needed to obtain the highly significant beneficial results on blood lipids and arterial dimensions; (ii) isoflavone treatments alone at high doses (relative to above) consistently improved bone parameters in rodent ovariectomized models, but not in humans or primates; (iii) isoflavones were not consistent in exerting positive effects regarding the prevention or treatment of cancers of the mammary glands, uterus and colon; and (iv) the effects of isoflavones on climacteric symptoms were not clear-cut.

The promise of soy isoflavones reducing chronic disease risk seems to be non-uniform, with the most conclusive benefits occurring in the prevention of cardiovascular diseases, but other organ systems, such as skeletal and reproductive tissues, may also benefit from the consumption of soy and soy-derived products.