Soy may thwart belly-fat gain after menopause

NEW YORK (Reuters Health) - A daily serving of soy may help postmenopausal women avoid gaining fat around the middle, preliminary research suggests.

In a study of 18 postmenopausal women, researchers found that those who drank a soy-based shake every day for three months tended to gain less abdominal fat than those who had a milk-based shake.

Soy contains compounds called isoflavones that are structurally similar to estrogen and bind to estrogen receptors in fat tissue. So in theory, soy isoflavones could help regulate body fat metabolism.

The new findings appear to be the first to show that soy protein may affect abdominal fat distribution, according to the researchers, led by Dr. Cynthia K. Sites of the University of Alabama at Birmingham. They report the results in the medical journal Fertility and Sterility.

The study included 18 women in their 50s who had been menopausal for one to five years. Half were randomly assigned to drink a soy-based shake each day, while the rest were given a shake containing the milk protein casein.

The women were told to drink half of a shake with breakfast, and the other half with dinner, and to substitute the daily drink for other foods in their diet in order to avoid weight gain.

After three months, the researchers found, women who drank the soy shake showed less of a gain in abdominal fat, even though both groups showed similar changes in weight and overall body fat.

It’s not clear why soy protein might affect belly fat in particular, according to Sites and her colleagues.

“Whatever the mechanism,” they write, “our data suggest that soy protein containing isoflavones may prevent the accumulation of fat in the abdominal depot.”

Because excess abdominal fat is especially related to higher risks of diabetes and heart disease, limiting the well-known middle-age spread is important, the investigators point out. They think larger, longer-term studies should continue to investigate the potential of soy protein.

SOURCE: Fertility and Sterility, December 2007.