Men who eat soya-based foods may be harming their fertility, doctors said this week, 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, 41-million fewer sperm per millilitre of semen than men who had never eaten soya products.
The study, by Jorge Chavarro at Harvard school of public health in Boston, builds on previous research in animals and on human tissues.
Male fertility has been in decline in the West for several decades, with about 20% of young Europeans having a low sperm count, 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 food including biscuits, sweets, pasta and bread.
Chavarro and colleagues at Massachusetts General hospital recruited 99 men who visited a fertility clinic between 2000 and 2006. The men were asked to fill out a questionnaire which asked them about the amounts of 15 different soya foods they had eaten over the previous three months. The researchers then divided the men into four groups according to the levels of chemicals called isoflavones in their diets.
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, compared with men who never consume soya food,” said Chavarro.
Richard Sharpe, of the Medical Research Council’s human reproductive sciences unit, said: “The take-home message could be that if you’ve got an already low sperm count — soya foods are probably not a good idea for you.” —