Nutrient - Soy foods - to eat or not to eat?
There has been much discussion, and high-quality research carried out, into the benefits or risks of consuming soy foods, both for female and male health. However, there is also much confusion, especially among women who have hormone related cancers, such as breast cancer, as to their effects and safety. Indeed, many clinicians have positively discouraged eating soy foods in any form following a diagnosis of breast cancer. However, in a recent review carried out in Women’s Health1 on breast cancer survival rates,it appears to confirm no adverse effects from consuming whole soy and there may even be some benefit.
The main beneficial components of soy foods are isoflavones, which are categorised as phytoestrogens. As well as perhaps being best known for their hormone-balancing effects in menopausal women, soy isoflavones appear to have positive effects for lowering cholesterol, as well as offering protection against bone loss and heart disease in postmenopausal women.
During the Ming dynasty, fermented soya appeared in the Chinese Materia Medica as a nutritionally important food and an effective remedy against disease. Fermented soya products have therefore been part of the staple diet in Asia for thousands of years. These soya foods are almost always cultured or fermented with micro-organisms before being eaten (for example, miso, tempeh and natto). As a consequence, the Japanese obtain significant amounts of active plant oestrogens from their diet. Fermented soya is easier to digest and has a lower phytate content. The fermentation process also removes undesirable elements from soya, which can interfere with digestion, and it improves the bioavailability of isoflavones. Contrary to popular belief, soya milk, soya protein powder and soya meat substitutes have very little active isoflavone content. However, the presence of protein may also contribute to soy’s positive effects supporting the principle that whole foods are better than extracts. Very few Western men or women eat fermented soy on a regular basis and isolated isoflavones lack the necessary protein matrix, which appears to offer maximum health protection. Perhaps another reason for choosing a food form supplement that has undergone the fermentation process rather than isolated extracts?
The active isoflavones from soya are genistein (the most important), daidzein and glycetein. 98% of isoflavones in soya beans occur in their inactive forms, hence the importance of fermentation to produce the active forms. Incidentally, natto contains five times more genistein than either tofu or soya milk. Inactive isoflavones can be activated in the gut by bacterial action, but if the gut flora is compromised, this is unlikely to be efficient.
Isoflavones are plant oestrogens, which have a gentle balancing effect with human oestrogen receptors, helping to modify the effects of insufficient or excess oestrogens in the body. In fact, it appears that genistein may also inhibit the growth of both testosterone and androgen-dependent cancer cells.
So, while there is still more research to be carried out in terms of other benefits, it would seem that we can all benefit from having more fermented soy in our diets.
1. Messina M, Abrams D I, Hardy M. Can clinicians now assure their breast cancer patients that soyfoods are safe? Women’s Health. 2010. 6(3), 335-338.