Men who eat soya-based foods may be harming their fertility, doctors said yesterday, after a study found a link between soya-rich diets and lower sperm counts.
The study showed men who consumed more than two portions of soya-based foods a week had, on average, 41m fewer sperm per millilitre of semen than men who had never eaten soya products.
A sperm count of between 80m and 120m per ml is regarded as normal, while men who produce fewer than 20m sperm per ml are regarded as clinically subfertile.
The study, by Jorge Chavarro at Harvard school of public health in Boston, builds on previous research in animals and on human tissues that has suggested certain ingredients in soya could harm sperm production.
Male fertility has been in decline in the west for several decades, while levels of soya have risen steadily in the western diet since the 1940s because it is a cheap source of protein. Soya-based products are now found in two-thirds of manufactured food including biscuits, sweets, pasta and bread.
Isoflavones are ingredients in soya products that mimic the female sex hormone, oestrogen. Each man then provided a sperm sample for testing.
Chavarro found that men who consumed at least half a portion of soya food a day had the lowest sperm counts.
“Our findings suggest that the greater the soya food intake is, the lower the sperm concentration” said Chavarro, whose study appears in the journal Human Reproduction.