Soya products may affect sperm

BioNews reporting from ESHRE (European Society of Human Reproduction and Embryology) conference, Copenhagen: A British scientist has claimed that eating some foods may affect a woman's chance of getting pregnant, because chemicals in them affect the ability of sperm to fertilise an egg.

Lynn Fraser, professor of reproductive biology at King's College, London, told the annual conference of the ESHRE, held in Copenhagen, Denmark, that a chemical found in soya products and leguminous vegetables, caused sperm to 'peak too soon'. One chemical in particular - called genistein - was found to affect the ability of sperm to penetrate an egg, particularly in combination with other chemicals found in hops and everyday household and industrial products. This is because it speeds up chemical changes within sperm, rendering them infertile by the time they reach an egg. This chemical change, known as the acrosome reaction, normally only occurs when a sperm reaches an egg, and is when sperm release enzymes that break down the outer layer of the egg allowing the sperm head to penetrate it more easily. However, if the acrosome reaction occurs too early, the sperm become ineffective and unable to enter the egg, as they have no digestive enzymes left.

Professor Fraser, who had carried out previous research on mouse sperm that suggested similar findings, said that tests on human sperm had proved it was 10 to 100 times more sensitive to genistein. 'Human sperm are responding to very low concentrations - well within the amounts that have been measured in people's blood', she said. She added that the chemicals would be more likely to affect sperm in the female reproductive tract, so 'maternal exposure to the compounds is probably more important than paternal exposure'. The findings might suggest that women who eat soya-based products and legumes should change their diet - particularly during the most fertile part of their cycle - if they want to get pregnant, said Professor Fraser, who is going to test the theory further by trying to mate mice fed on a high-soya diet.

A spokesperson for the Vegetarian Society agreed that there might be something in Professor Fraser's theory. 'For anyone struggling to become pregnant, avoiding soya products for a few days a month is worth a try if there is even a slim chance that it will help fertility', they said, adding that vegetarians and vegans should try alternative foods. However, Professor Richard Sharpe of the Human Reproductive Science Unit in Edinburgh, interviewed by the Guardian newspaper, pointed out that 'Oriental societies that traditionally eat a soy-rich diet show no signs of reduced fertility of which I am aware'.