A chemical contained in soya damages human sperm while on their journey through the fallopian tubes to fertilise an egg and could thus affect a woman's ability to conceive, a British female academic has found.
Lynn Fraser of King's College in London told a European fertility conference in Copenhagen that women should avoid soya products, like soya sauce and tofu, when trying to conceive.
The chemical genistein causes sperm to lose their acrosomes, the caps that allow them to penetrate the egg.
Fraser showed three years ago that genistein, along with other chemicals found in beer, paint and pesticides, affected mouse sperm in the same way, but she was surprised to find that human sperm was extremely sensitive to genistein.
"I expected human sperm to respond, but I was surprised to find it appeared more sensitive," she said, saying that even tiny doses of genistein could cause sperm to "burn out".
Fraser, a professor of Reproductive Biology, said acrosome reaction generally took place as the sperm sheds a membrane as it "docked" with the egg.
"If the acrosome reaction occurs before a sperm reaches an egg, then fertilisation is unable to take place because the sperm has lost special docking molecules that allow it to bind to the egg," she said.
The findings could have significant implications for vegetarians, as many non-meat products contain soya.
Fraser said it was not a question of avoiding soya products entirely. "But it might be best for a woman to avoid them for a few days around the time she is ovulating."