Would-be mums told to avoid soya

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http://www.newscientist.com/article.ns?id=dn7559

 

13:05 22 June 2005

NewScientist.com news service

Michael Le Page, Copenhagen

 

Women trying to conceive should consider not consuming soya for the

few days around ovulation, according to a UK researcher. Her study

shows a compound found in soya causes human sperm in a dish to

" pop

their caps " prematurely, rendering them useless. But it remains

unclear whether eating soya has any actual effect on fertility.

 

Lynn Fraser of King's College London studied the effect of very

low

levels of genistein - a compound found in leguminous plants such as

soya - on human sperm in a liquid medium similar to that found in the

female reproductive tract. " It was very striking, " she says.

" Within

an hour a third of the sperm had gone all the way. "

 

This means that the genistein had prematurely triggered the sperm to

undergo what is known as the acrosome reaction. The acrosome is the

cap on the tip of sperm that contains the enzymes needed to penetrate

the thick outer layer of the female's egg once the sperm has

reached

it. If it is lost early, sperm have no chance of fertilising an egg.

 

Fraser says other studies have shown that genistein gets into the

blood of people who eat soya products. She believes that in women, it

could end up in the reproductive tract and damage their chances of

conceiving. " From what we have seen, women should restrict their

diet

for a short time over the period of ovulation. "

Effects on males

 

But other experts are not convinced such advice is necessary. James

Kumi-Diaka of Florida Atlantic University, US, says his team has also

found that genistein has a dramatic effect on sperm - so much so that

he has toyed with the idea of incorporating genistein into condoms as

a contraceptive.

 

His team has also found that when genistein is injected into male rats

three times a week, it reduces the size of the litters they father,

from about 11 pups at most to five. Even low doses had an effect, he

says. That would seem to hint that men, too, should worry about eating

soya when trying to father children.

 

But Kumi-Diaka stops short of such advice. " It depends on so many

things, " he says. " How the food is prepared, how often you

eat it,

whether it is eaten alone. " If genistein really does affect

fertility,

Kumi-Diaka points out, you would expect to see fertility problems in

Asian countries, where many people consume soya products daily - but

there is no such evidence.

Combining chemicals

 

Fraser first reported that genistein triggers the acrosome reaction in

mouse sperm in 2003. In other studies on mouse sperm, she has found

two other chemicals can also trigger the acrosome reaction. One,

called 8-prenylnaringenin, is found in hops and is thus is present in

some beers, but Fraser does not know what levels are typical. The

second chemical, nonylphenol, is found in products such paints,

pesticides and cleaning products. " There could be a whole range of

chemicals with this effect, " she says.

 

What is more, Fraser found that combinations of these chemicals, which

she calls xenobiotics, had a much greater effect than any one alone.

" Given the likelihood that we are exposed to several xenobiotics

at

any one time, we need to investigate their possible effects on

fertility as quickly as possible. "

 

Her latest studies were presented at a meeting of the European Society

for Human Reproduction and Embryology in Copenhagen, Denmark, on

Wednesday.