A little wiser: Does too much soya give men breasts?

Katja Teerds, associate professor of Human and Animal Physiology explains.
Illustration: Marly Hendricks

Soya products contain isoflavones, which are phytoestrogens, the plant equivalent of oestrogens. ‘These substances bind to the oestrogen receptors in the body,’ says hormone expert Katja Teerds, associate professor of Human and Animal Physiology. ‘But that doesn’t mean that oestrogen activity goes up and you develop breasts. To start with, soya products contain tiny quantities of isoflavones, so you would really have to drink litres of soya milk before you would notice any effects at all. And also, phytoestrogens do not bind nearly as strongly to oestrogen receptors as the body’s own oestrogens.’

Teerds has some idea where the stories about soya-induced ‘man boobs’ come from, though. ‘Overweight men often have higher oestrogen levels. That is because fat tissue gives off an enzyme, aromatase, which converts testosterone into oestrogen. Breast formation in these men is partly a matter of fat deposits, and partly a result of the slightly raised oestrogen level. The breasts consist largely of fat tissue and to a lesser extent of mammary gland tissue. A high oestrogen level also causes a lower libido in men and possibly reduced fertility. Which also happens with anabolic steroids, incidentally.’

Breast formation in men is partly due to raised oestrogen levels

Katja Teerds, association professor of Human and Animal Physiology.

What about women, can they go up a cup size if they drink soya milk? ‘No, it’s the same for them: you’d have to consume far more soya products than you possibly could. There are oestrogen supplements for women in the menopause, some of them with phytoestrogens. If your own oestrogen levels are low, as they are during the menopause, taking these could help to reduce menopausal symptoms. The safety of synthetic oestrogen supplements – not the plant ones – is disputed, however, because it is claimed they could raise the risk of breast cancer.’

Phytoestrogens are found not only in soya, but also in products such as peas, linseed, broccoli and beer. Maybe that was the inspiration for the Dutch carnival hit called ‘Beer and tits’.

Conclusion: No matter how many litres of soya milk you down, you won’t get bigger breasts even if you wanted to. 

Every day we are bombarded with sometimes contradictory information. So what are the facts of the matter? In this feature, a scientist answers your burning questions. Asking questions makes you wiser. Do you dare to ask yours? Email us at redactie@resource.nl

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