Phyto-oestrogens found in soya products have been known for some time to have an effect on humans' hormones. And, as hormone-related cancers such as breast and womb cancer as well as osteoporosis and menopausal problems appear to occur at lower rates in Asian countries, it was suggested that this was a result of a high dietary intake of these phyto-oestrogens via soya. For this reason, many post-menopausal women have increased their intake with the hope of reducing menopausal symptoms as well as helping to prevent bone loss. But new research indicates that they may not be as beneficial as previously thought.
Looking at 248 women in the first five years after menopause, researchers gave one group of women, all aged between 45 and 60, a soya isoflavone supplement and the other group had placebo tablets. The soya group had 200mg of soya isoflavone every day – the equivalent of double the highest intake through diet (as assessed through the typical Asian diet, where soya products are eaten regularly). They took these supplements over a period of two years.
Checking bone mineral density in the spine, the hip, or the femoral neck (in the leg), as well as collecting data about the women’s menopausal symptoms (hot flushes and night sweats, for example), the researchers found no evidence that soya had any benefit. In fact, when they looked at hot flushes, specifically, more women in the soya group (48%) reported continuing problems while only 32% of the placebo group did. The soya group also reported more constipation. There were no significant differences in bone density between the two groups.
Other studies that have shown some benefit have been poorly designed, with a too-small sample size or too short a duration to be conclusive, say the researchers. Their study aimed to address these problems.
As for the difference in the prevalence of certain cancers and menopausal-related problems between Asia and other continents, this is unlikely to be the result of higher intake of soya. Because, while the Asian diet does generally feature more soya, it is usually fermented soya – unlike soya milk, burgers or foods made with soya flour, this type of soya does not contain large amounts of the phyto-oestrogens.
First published August 11, 2011