NEW YORK (Reuters Health) - If studies in rats are an indication, a diet rich in black soya beans may help control weight, lower "bad" cholesterol levels and help ward off type 2 diabetes.

Korean investigators led by Shin Joung Rho at Hanyang University, Seoul, had 32 rats gorge on a high-fat, high-cholesterol diet for 28 days. Some of the rats were given supplements with various levels of black soy beans and some were not (the controls).

After two weeks, rats getting 10 percent of their energy from black soy had gained half as much weight as those in the control group that were not given black soy.

The rats on the 10-percent black soy diet also had 25 percent lower total cholesterol and 60 percent less "bad" LDL cholesterol than the comparison animals. Blood levels of "good" HDL cholesterol were also markedly higher in rats fed black soy.

This study suggests that incorporating black soy beans in the diet may "inhibit weight gain significantly," and favorably alter cholesterol levels, write Rho and colleagues in the Journal of the Science of Food and Agriculture.

The researchers say more study is needed to determine the long-term effects of black soy in the diet of humans as well as studies comparing the benefits of black soy and yellow soy in the diet.

Experts say soy protein may have favorable effects on fat metabolism in the liver and fat tissues. Black soy beans have been used as a component in Asian medicines to treat diabetes and high blood pressure, curb inflammation, and aid blood circulation, as well as to treat hormone disorders after childbirth.

In 1999, the US Food and Drug Administration ruled to permit food products containing soy protein to carry a label promoting the heart benefits of soy. The approval "is based on evidence that soy protein in a diet low in saturated fat and cholesterol may... help to reduce the risk of (heart disease)," FDA wrote in a statement at the time.