Soy has no known effect on testosterone levels in men.
This myth has come about because soya contains natural phytoestrogens, known as isoflavones, which resemble oestrogen chemically. Some people thought – before proper research was conducted – that they would affect testosterone in the same way that oestrogen does. But they don’t because they are not oestrogen. In fact, one study suggests that soya isoflavones have just 1/10,000 the potency of ‘real’ oestrogen.
Another study involved seven healthy young men who ate A LOT of soya beans every day for a week. At the end, they showed no changes in estrogen or total and free testosterone at all, but the study did find an increase in brain activity, specifically an improvement in spatial cognitive performance. Interesting…
A meta-analysis of all published research relating to soya and testosterone was undertaken in 2010. It looked at 15 placebo-controlled studies and 32 reports on 36 treatment groups and concluded: ‘Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men’. So, that’s pretty clear.
However, what those who cling to this myth don’t say is that those same phytoestrogens can have powerfully beneficial effects. In Asia, where consumption of soya products is greater than in the US and UK, prostate cancers are less common in men. In fact, consumption of soya is associated with a 20-30 per cent reduced risk of prostate cancer. And, incredibly, research has shown that consuming soya can actually help slow down the rate of prostate cancer if it has already taken hold. Good old soya!
Correspondingly, research shows that women who consume more soya suffer less breast and uterine cancers. There have been lots of studies done on this issue and one found that women who have just one cup of soya milk per day (or half a cup of tofu) have 30 per cent less risk of developing breast cancer compared with women who have little or no soya. And the sooner we start the better, as breast tissue forms in adolescence. But it is also never too late. The Women’s Healthy Eating and Living Study found that women who had previously been diagnosed with breast cancer would do well to included soya products in their diet as those who consumed the most soya products cut their risk of cancer recurrence or mortality in half.
So, soya is a good guy. It definitely doesn’t lower testosterone and it does protect against cancer.
Search Veganuary’s recipes section for some delicious tofu-based meal ideas.