- Vegetarians of the world take notice: Compared to those
who go light on soy, people who eat tofu at least twice a week may double
their risk of developing cognitive trouble in old age, a new study shows.
- Hawaii researchers say chemicals in soy may interfere
with the brain's ability to make and keep nerve connections, which in turn
could lead to both functional and physical brain changes over time.
- Experts caution that the finding, which appears in the
April issue of the Journal of the American College of Nutrition, is very
preliminary and hasn't been replicated. Still, they say, it does challenge
the notion that tofu is all virtue and no vice.
- "I have never seen a time when so little evidence
has been the engine for such an incredible amount of hype" about the
alleged powers of a nutrient, says Dr. Lon White, a brain expert at the
Pacific Health Research Institute in Honolulu and lead author of the study.
- "There is a tidal wave of desire to believe that
if we substitute tofu for red meat or eggs it's going to have beneficial
effects. But there is a great deal of concern in the scientific community
that those health benefits have been wildly overstated," White says.
- Soy is the darling of vegetarian cuisine. The highly
versatile food is touted for its powers not only to make a meatless meal,
but for its ability to prevent everything from osteoporosis to heart disease
- Many of these claims are wildly exaggerated, experts
say. Yet soy isn't without some health benefits. Last October, for instance,
the Food and Drug Administration said it would allow companies to market
soy as being useful in preventing cardiovascular disease.
- In addition to being chock-full of protein, the plant
is rich in a family of chemicals called isoflavones. These molecules mimic
estrogen, a hormone that can increase a woman's risk of breast cancer.
So, the thinking goes, by getting ersatz estrogen women can avoid the
potential harm caused by the real thing.
- Researchers are also increasingly turning up a role for
estrogen in the brain, where it seems integral to nerve health.
- In the latest study, White and his colleagues looked
at the relationship between cognitive performance and other measures of
brain function and tofu intake in more than 3,700 Japanese-American men.
The subjects had been interviewed in the 1960s as part of the Honolulu
Heart Program, a prospective study involving some 8,000 men of Japanese
descent. They have been followed ever since.
- Risk for frequent eaters nearly double
- Age, level of education and history of stroke had the
most impact on mental performance. But even after accounting for those
factors, men who ate the most tofu in middle age -- and their wives who
also ate a lot of soy -- scored worse on cognitive tests than those who
ate less soy in midlife.
- On an individual level, "it looks like this is a
very minor effect," says White. Yet, men and women who had eaten tofu-rich
diets were up to 1.8 times more likely to score poorly on mental function
tests than those who ate it only occasionally.
- Tofu, too, was linked to smaller brain size, as measured
by imaging and autopsy. "It's a very strong signal that there is something
going on that's related to what happens to the brain when it ages,"
- Soy's effect on estrogen -- blocking the action of the
body's version of the hormone -- might be involved in the worsening brain
function. White's group also speculates that the plant matter is acting
on an enzyme, tyrosine kinase, that helps keep nerve cells robust and
preserves the connections between them.
- In an editorial accompanying the Hawaii study, Harvard
University researchers call the findings "provocative" and worthy
of further inquiry. However, they note, a number of issues cloud the case
- Is stroke the real culprit?
- For example, the men who ate the most soy products were
also more likely to suffer strokes -- suggesting that perhaps the brain
changes were related to a vascular problem and not to soy intake. And
tofu is a relatively cheap food typically consumed by poorer Japanese
immigrants who can't afford other sources of protein. As a result, the
increased risk of neurological problems might reflect an overall lack
of good childhood nutrition and not a directly detrimental effect of tofu.
- White says he and his colleagues tried to address those
factors, and still came up with the same conclusion. "I think the
tofu effect is probably atrophy, but it may also have an independent effect
on starting reserves" of brain cells, he says.
- Soy may not help breast cancer
- In separate study, presented today in San Francisco at
a meeting of the American Association for Cancer Research, researchers
at the University of Illinois in Chicago report that the component of soy
protein thought to reduce the risk of breast cancer may be less effective
at fighting tumors than previously believed.
- Women who regularly eat soy protein appear less vulnerable
to breast cancer, and scientists have linked this protection to isoflavones,
particularly one called genistein.
- But Andreas Constantinou, the Illinois researcher who
led the latest work, says tests in rodents show that soy protein stripped
of isoflavones offers significantly more tumor protection than soy protein
with the compounds. What's more, Constantinou found, genistein was much
less effective at blocking tumor growth than its relatively ignored sibling
- What To Do
- The bottom line, says White, is that isoflavones act
like drugs, so consumers should view them that way.
- "We as a society have evolved to the point that
we truly want to believe that the key to health is what you eat,"
he says. In fact, however, scientists know little about the effects of
nutrients on health except in cases of deficiency. The benefits of tinkering
at the margins are up for debate, he says.
- Constantinou is somewhat less wary of soy products, at
least in moderation. "If you eat soy, [isoflavones] are not going
to harm you. But if you're taking them in pill form instead of soy, you
may not be giving yourself as much benefit," he says.
- This HealthSCOUT article discusses how the government
finds soy healthful enough to allow more in school lunches.
- To learn more about soy from an industry perspective,
visit the United Soybean Board.
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