Many aging women add soy to their diets for its widely touted health benefits. But a recent study finds that better brain function isn’t one of them.
Researchers at the Stanford University School of Medicine and the USC Keck School of Medicine conducted a 2.5-year study of middle-aged and older women and found that those taking soy supplements performed no better on tests of cognitive function than women who didn’t add soy.
The study involved 313 women aged 45 to 92 participating in the Women’s Isoflavone Soy Health trial. The women were randomly assigned to receive a daily 25 g dose of isoflavone-rich soy protein or a placebo of milk protein; neither the researchers nor the women knew who was taking which supplement. At the start of the study, and again at the end, women took neuropsychological exams, including tests of reading, thinking and memory.
Researchers found that by the end of the study, women on the soy supplements showed a slight improvement on the test of visual memory (remembering faces), compared with those taking the placebo, but otherwise experienced no boost in performance. Overall, however, women in both groups generally did better on the tests the second time around, possibly because they’d already taken them before.
“In regard to cognition, the literature on soy has been somewhat schizophrenic,” says lead author Dr. Victor Henderson of Stanford University. “Most studies have been small and have conflicting findings. Our study is one of the largest, and finds that overall, soy has no effect on cognitive function. The take home is that soy is nutritious and has a lot to recommend, but should not be taken with the expectation of cognitive benefits.”
Previous research on other touted benefits of soy have been similarly spotty. Many women use soy and soy-based products to ease the symptoms of menopause, but a 2011 study found that taking daily soy isoflavone tablets had no impact on women’s bone density or on the frequency of hot flashes or night sweats. The evidence has also been mixed on the influence of soy on breast cancer and heart disease risk and on cholesterol levels.
Researchers had initially thought that soy could potentially benefit cognition because of its isoflavones, estrogen-like compounds that are known to activate estrogen beta receptors in the brain’s hippocampus, a region crucial to memory. Given the current results, however, Henderson and his colleagues advise postmenopausal women not to increase soy consumption in hopes of boosting their brain power.
Still, soy is high in protein, fiber, vitamins and minerals, and it’s low in saturated fat, which makes it a healthy part of any diet. The authors say women who enjoy eating soy should continue to do so.
Henderson says the next step is to look more closely at whether soy may have benefits in certain women but not others, in men or in younger women.
The study was published in the journal Neurology.