A superfood or a hormone-disrupting poison? A bean that decreases your risk of cancer or increases it? A food that's a perfect protein and calcium source for vegans, vegetarians and those suffering from dairy intolerances or one which interferes with sexual development and fertility?
When it comes to soya beans, balanced and independent information is often hard to come by, leaving us confused as to how much soya bean we should be eating - if we should be eating it at all. So what's the truth about the much maligned yet also much praised bean?
Undoubtedly, soya has a lot going for it. A member of the legume family, along with peas, pulses and other beans, it's an excellent source of protein and one of the few vegetarian sources of all eight essential amino acids required by the body (others include hemp, quinoa, millet and amaranth). Soya foods also contain polyunsaturated fatty acids such as omega 6 and omega 3, B vitamins, iron and antioxidants, and they're free of cholesterol, too.
'Calcium-fortified soya products such as soya milk and tofu provide a valuable source of this important mineral without the saturated animal fat and cholesterol found in dairy products,' says vegan nutritionist Justine Butler. 'Many soya foods also contain fibre, important for bowel health and helpful in reducing cholesterol.'
There is also good evidence that the bean is beneficial to heart health, and can reduce the risk of cardiovascular disease, and that including a moderate amount of soya protein - say 25 grams - as part of a diet low in saturated fat, can help reduce blood cholesterol. There also appears to be a link between soya beans and reduced menopausal symptoms (such as hot flushes), and possibly also to a reduced risk of osteoporosis. However, although it has been found that soya beans can boost bone mineral density, not enough good long-term trials have been done to put that beyond doubt.
So far, soya good - or so it seems. But not everyone is convinced. The main source of criticism centres on the bean's isoflavones, which are plant oestrogens (phytoestrogens) that can produce biological hormonal effects in humans. Soya isoflavones have a similar structure to the female hormone oestrogen, but they don't act in the same way; isoflavones are weakly oestrogenic and have the potential to act as 'anti-oestrogens' by binding to the receptors that oestrogen binds to.