How to Diet: Does Soy Put You at Risk for Cognitive Decline?

The rap: “If we want to protect our brains, we might want to not consume a lot of soy.”
—anti-soy activist Kaayla Daniel


The real story: The soy world got a jolt in 2000, when University of Hawaii researchers reported that among more than 3,300 Japanese-American men, those who ate two or more servings of tofu a week during middle age were at greater risk of cognitive decline—and brain atrophy— years later.

Two surveys of Indonesians—with conflicting results and unsophisticated analyses—only muddied the waters.

To see whether soy affects memory and thinking, researchers need to pit it against a (soy-less) placebo, says Wendy Mack, professor of preventive medicine at the University of Southern California. Two studies have done that and their results are reassuring.

In 2011, Mack and her colleagues randomly assigned 313 healthy women aged 45 to 92 to consume 25 grams a day of either soy protein (with 91 mg of isoflavones) or milk protein. After 2½ years, “the soy takers scored no differently than the dairy takers on a battery of tests assessing a broad spectrum of cognitive skills,” says Mack.

And Dutch scientists found no difference on similar tests when they gave 175 older women 26 grams a day of soy protein (with 99 mg of isoflavones) or milk powder for a year.

Sources: J. Am. Coll. Nutr. 19: 242, 2000; Dement. Geriatr. Cogn. Disord. 26: 50, 2008; Brain Res. 1379: 206, 2011; Neurology 78: 1841, 2012; JAMA 292: 65, 2004.


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5 Replies to “How to Diet: Does Soy Put You at Risk for Cognitive Decline?”

  1. The study that indicated risk of cognitive decline was on men. The follow-up studies that indicated no risk were on women. Could it be that soy affects men and not women?

  2. Good point, Steven. In addition, the original study mentioned cognitive decline (in men) showing up “years later”, whereas the follow-up studies were only for 2½ or 1 year. Let’s see some studies on both men and women for a long-term time frame.

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