Soy On Its Own May Not Help Prevent Postmenopausal Weight Gain

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Menopause has been associated with an increase in body weight for many women. Some small animal and human studies have found some evidence that isoflavones in soy foods could possible help reduce fat mass associated with the change in hormone levels. A new study has found that soy by itself may not provide much of a weight loss benefit for postmenopausal women.

Dr. Oksana A. Matvienko of the University of Northern Iowa in Cedar Falls and colleagues enrolled 229 postmenopausal women, none of whom were severely obese in a study of soy isoflavones. The women were randomly assigned to receive a either an 80- or 120-milligram isoflavone tablet every day for a year versus a placebo.

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The isoflavones had no significant effect on the women’s body weight, nor did they find that the soy pills affected levels of insulin, leptin, ghrelin, or adiponectin – hormones that regulate the appetite. The only factor that predicted fat mass change in the women was the amount of fat in a woman’s diet.

The three main types of soybean isoflavones are genistein, daidzein, and glycitein. Genistein has the strongest estrogenic activity of all the isoflavones and, in addition to soybeans, is also found in other legumes such as the chickpea. Daidzein has both weak estrogenic and anti-estrogenic effects. It appears to stimulate the formation of osteoblasts, which are cells that produce bone mass. Glycitein accouns for only about 5-10% of the total isoflavones in soy foods.

Most likely, the positive effect that soy can have on body weight is when it is used to reduce the amount of both total and saturated fat in the diet by replacing fatty animal meats. Soy foods can also replace dairy such as whole milk and cheese, not only reducing fat, but also can reduce the total number of calories a women consumes in a day.

SOURCE: Menopause, online February 5, 2010.

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