http://www.newscientist.com/article.ns?id=dn7559
Would-be mums told to avoid soya
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.
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Soy is not real food. And it ain't a healthy food, by anyone's
standards.
TC