news that tofu (bean curd, made from soybeans) may increase the
risk of dementia confused many health-conscious people. A new
study found that middle-aged Japanese-American men who reported
that they consumed at least two servings of tofu a week had a
faster decline in certain mental abilities and greater brain atrophy
20 years later, compared to those eating little or no tofu.
The study, published in April and based on data from the Honolulu-Asia
Aging Study, got lots of media attention, since the accused was
no ordinary food. Soy is supposed to keep people healthy. Only
a few months earlier the FDA had begun to allow many soy products
to carry a health label stating that they may help prevent heart
disease. And, according to its many advocates, soy can also ease
symptoms of menopause and protect against osteoporosis and cancer,
though the evidence for all this is either inconclusive or minimal.
This new study raises more questions than it answersand
certainly shouldn't make you avoid tofu or other soy foods.
If tofu does have an adverse effect on the brainand that's
a big ifit is slight, according to this study. Still, why
hasn't this effect been seen in Japan, where people live long
lives and eat lots of tofu? Soy foods are a staple for much of
the world's population. Tofu does contain estrogen-like substances
called isoflavones, which, animal studies suggest, might affect
brain activity. But little is known about their effect in the
human brain. These researchers did not measure isoflavones in
the men's blood or in the food they ate.
One problem with observational studies like this is that it's
impossible to know whether tofu somehow causes this slight premature
aging of the brain, or if there's something else about men who
eat tofu that's responsible. The researchers adjusted the data
for various complicating factors (certain other foods, age, weight,
education, alcohol, smoking, etc.), but couldn't possibly control
for everything. For instance, men who ate the most tofu tended
to come from poorer immigrant families, so they may have had a
poor diet in childhood; this may have somehow affected brain development.
Another problem: the amount of tofu consumed was self-reported,
and was based on only two interviews, five years apart, decades
bottom line: Plant foods are complex mixtures of substances
that scientists are only beginning to understand. Isoflavones,
in particular, have many potential effects in the bodynot
only on the brain, but also on cancer risk and bone health. On
balance, soy is good food. But don't take soy or isoflavone supplements.
Reference Source 98,99,101