Not everyone is scared of soy. Some people go out of their way to get more. Here’s what soy can—and can’t—do.
Menopausal symptoms. “It’s clear that soy and its isoflavones protect against hot flashes in women during menopause,” says Christopher D’Adamo, an assistant professor at the University of Maryland School of Medicine in Baltimore.
Since 2000, 13 studies have given a placebo or a daily isoflavone supplement to a total of nearly 1,200 menopausal women in six countries for six weeks to one year. Those taking the isoflavones reported 21 percent fewer hot flashes. And in the nine studies that looked, hot flashes were less severe.
Cardiovascular disease. In 1999, the Food and Drug Administration ruled that 25 grams of soy protein a day can lower cholesterol levels enough to reduce the risk of heart disease. But since then, the evidence for soy has weakened.
For instance, the Women’s Isoflavone Soy Health (WISH) trial gave 325 healthy postmenopausal women 25 grams a day of either soy protein (with 91 milligrams of isoflavones) or milk protein for three years.
“We didn’t find strong evidence for any significant cholesterol-lowering effect from the soy,” says USC’s Wendy Mack. And thickening of the carotid artery wall, a measure of atherosclerosis, “progressed at the same rate in both the soy eaters and the dairy eaters.”
Eating soy-based veggie burgers or tofu in place of red meat, on the other hand, should help lower your cholesterol and your risk of colon cancer. But that’s probably because you’re eating less red meat and more of soy’s polyunsaturated fat.
Bones. The evidence that soy isoflavones can protect women’s bones is unimpressive.
In two recent studies of a total of 332 women, taking 80 to 200 mg of isoflavones every day for two or three years had no more impact on the density of their hip bones and spines than taking a placebo.
Sources: Menopause 19: 776, 2012; Stroke 42: 3168, 2011; Am. J. Clin. Nutr. 91: 218, 2010; Arch. Intern. Med. 171: 1363, 2011.