Mums to be: no soya

Pregnant women were told yesterday not to eat soya amid fears it can damage their babies' sex organs.

Scientists discovered mutations among male rats whose mothers were fed a chemical from the plant, used in soya products such as flour, oil and tofu.

They grew up to have unusually large prostate glands and small testicles.

They also seemed unable to ejaculate, New Scientist magazine reported.

The levels of genistein - a plant version of oestrogen found in soya - given to the rats were equivalent to those consumed by vegetarians eating soya-rich diets.

'Urologists on this project are actually advising pregnant women to avoid soya,' said Dr Sabra Klein, who led the US-based researchers.

They found that rodents which did not eat genistein after weaning suffered just as severe effects as those which continued eating it - suggesting the biggest impact was from exposure in the womb and during breast feeding.

There is no evidence that soya causes anything similar to happen in humans. For example, no such sexual mutation has been observed in the sons of Asian and vegetarian women, the two groups most likely to consume a lot of soya.

But there is concern about the genistein found in baby formula drinks and in supplements taken as an alternative to hormone replacement therapy.

'These are serious questions that need answering,' warned Chris Kirk, of the University of Birmingham.