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In Light of Troubling Study on Soy, Moderation Seen as Key
LA Times Monday, March 27, 2000
In Light of Troubling Study on Soy, Moderation Seen as Key
By ROSIE MESTEL, Times Health Writer
If hormone replacement therapy has gotten a drubbing of late, so too
has a much-celebrated food that many women eat to help ease the
symptoms of menopause and to protect against heart disease and
osteoporosis: the soybean.
Some scientists are increasingly wary about Americans going hog-wild
for soy, soy protein and the estrogen-like chemicals (isoflavones) that
soy protein contains. A soon-to-be-published study linking tofu to a
faster decline in mental abilities is particularly unwelcome news for
any woman who sees eating soy as risk-free, either as well as or in
addition to conventional hormone replacement therapy. How seriously
should she view this new twist to the soy story? Should she toss out
her tofu? Swear off soy burgers?
Most soy scientists simply preach moderation. "The majority of
evidence indicates that soy is a safe food that's eaten by two-thirds
of the world's population," says Dr. David Heber, director of UCLA's
Center for Human Nutrition, adding that it does appear to have health
benefits. But Heber and others warn against eating soy to the exclusion
of other foods: A varied diet is important to good health. And they
caution against consuming very large amounts of soy protein or popping
isoflavone pills available in stores. "There's a tendency in our
culture to think if a little is good, then a lot's better," says Mary
Anthony, a soy researcher at Wake Forest University School of Medicine
in Winston-Salem, N.C. "But I personally am very concerned about
isoflavone pills and soy protein supplemented with extra isoflavones."
Isoflavones, after all, seem to act like hormones or drugs in our
body--even if for regulatory purposes they are classified as
nutritional supplements.
Some of the druglike effects of soy protein or the isoflavones they
contain could be good for us. Several dozen clinical studies have
reported, for instance, that eating an average of 25 grams of soy
protein daily for several weeks to months lowers blood levels of "bad"
(or LDL) cholesterol and may help elevate "good" (or HDL) cholesterol
levels--in other words, may help protect against heart disease. Based
on such studies, the U.S. Food and Drug Administration now allows foods
with at least 6.25 grams of soy protein per serving to be labeled with
claims stating that they could help reduce the risk for heart disease.
Soy protein (probably because of its isoflavones) might also help keep
bones strong, as well as ward off prostate or breast cancer
Yet some scientists warn that soy may have a dark side. For
instance, the new study of more than 3,000 Japanese American men living
in Hawaii "raises the specter that there may be--even if there are
benefits--a cost to be paid," says Dr. Lon White of the Pacific Health
Research Institute on Honolulu, author of the study. In that study, the
diets of the men who ate tofu at least twice a week were assessed in
midlife and their mental abilities assessed several decades later. In
addition to the more rapid decline in mental abilities, compared with
non-tofu-eaters, the men experienced a reduction in brain size. Other
potential downsides to soy, some scientists say, include the
possibility that soy chemicals might reduce the body's ability to
absorb minerals, might cause fertility problems, alter sexual
development, cause abnormalities of the thyroid and contribute to
cancers of the breast or pancreas. In particular, these scientists have
warned against feeding babies soy-based formula. The Food and Drug
Administration, in reaching its decision to allow soy products to carry
health labels, concluded there was insufficient evidence to warrant
such concern (though it didn't weigh in on the issue of soy
formula).
"Most of the concerns are red herrings," says Stephen Barnes,
professor of pharmacology and toxicology at the University of Alabama
in Birmingham. Two studies addressing the breast cancer risk, for
instance, did detect increases in the amount of fluid that women eating
soy secreted from their nipples--a potential danger sign. But the more
detailed study didn't find any change in a variety of other
measurements that are more direct signs of heightened risk, such as
increased growth of breast cells. Although soy does contain chemicals
called trypsin inhibitors that might adversely affect the pancreas,
there is little evidence that this happens in humans. Nor is there
proof that the chemical called phytate in soy interferes with
absorption of minerals like iron or that isoflavones interfere with
hormones of the thyroid gland and cause a disorder known as goiter.
What's more, these possibilities--since many plants contain similar
chemicals--are not confined to the soybean. "There are a lot of foods
that could potentially cause goiter--including cabbage," Heber says.
Dr. Claude Hughes, endocrinologist and chairman of the Center for
Women's Health at Cedars-Sinai Medical Center, says he does worry about
exposure of babies to isoflavones through formula. He also worries
about too much soy for women who have had breast cancer. As for the
possible dementia link, "we sure can't blow it off." The best bet, for
now, he suggests, is for women to make decisions about eating soy that
best matches their individual risk. "Personally, I eat tofu or edamame
several times a week--people in my family get heart attacks and
strokes, whereas Alzheimer's disease has never been an issue in my
mom's or my dad's family," he says. "I would offer that if there's a
family history of heart disease then the concern should be about doing
everything you realistically can to minimize progression of heart
disease. But if lots of people in your family get Alzheimer's, then you
may decide, 'Well, I don't want to do this.' "
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