Adding soy-protein-rich foods while cutting calories doesn’t accelerate weight loss, a new study shows.

Overweight women who ate 500 fewer calories a day than normal while consuming an extra 18 grams of soy-rich food daily for 12 weeks didn’t lose any more weight than their peers who didn’t add the extra soy, Dr. Marie-Pierre St. Onge of St. Luke’s/Roosevelt Hospital in New York City and colleagues found.

“Our results do not lend support to the emerging notion that soy-protein-rich foods could be considered potential functional foods for weight management, in the quantities consumed in this study,” St. Onge and her team conclude in the March issue of the Journal of the American Dietetic Association.

Some studies have suggested adding soy to the diet could promote weight loss, and the Food and Drug Administration has approved health claims stating that eating 25 grams of soy protein daily in conjunction with a diet low in saturated fat and cholesterol can cut heart disease risk, the researchers note.

To investigate whether adding soy to the diet could enhance weight loss while promoting heart health, they randomized 75 women to the low-calorie diet plus 15 grams of soy per 1,000 calories consumed daily, or a low-calorie diet only.

The women in the soy group were provided with the foods to eat, but towards the end of the study, many did not consume the prescribed 18 grams daily. Just 49 women completed the study.

While the soy-rich diet did tend to lower levels of insulin and “bad” cholesterol, there was no significant difference between the two groups in the amount of weight loss, reduction in fat mass, or waist circumference.

It may be necessary to eat more soy to achieve significant weight loss benefits, while consuming soy in a protein shake might also be more effective than eating soy-rich foods, the researchers state.

They conclude: “Current recommendations to consume 25 g/day soy protein as a means of reducing cardiovascular disease may not receive much adherence.”

SOURCE: Journal of the American Dietetic Association, March 2007.