While those on the soya shakes had lost abdominal fat during the course of the study, the other women had put it on, the American Society for Reproductive Medicine's annual conference heard.

The US researchers said the finding could prove particularly significant in improving the health of older women who often pile on the pounds after the menopause.

Writing in the journal Fertility and Sterility, they said: 'Our trial suggests a new dietary option for the prevention of abdominal adipose tissue gain that occurs after menopause.'

Dr David Christie, of the University of Alabama at Birmingham (CORR), who is collaborating with the researchers on other work on soya, said the shakes contained more soya than people would normally eat in their diet and supplements would be needed to get the same effect at home.

He added: 'This was a very small trial with very small numbers.

'If it were to hold up in larger numbers it could have much broader implications in terms of recommending soya to menopausal women.

'It may well have a reduced risk of cardiovascular disease or diabetes.'

Other recent research showed that a pot belly greatly increases the risk of heart attacks.

A 12-year-study of more than 100,000 men and women revealed that waist size is strongly linked health, with those with the biggest bellies being more than 40 per cent more likely to suffer from hardening of the arteries, angina and heart attacks than those with washboard stomachs.

At greatest risk were those who developed a beer gut, while still young, the US study showed.