The researchers, led by Shin Joung Rho at Hanyang University, Seoul, allowed 32 rats to gorge on a fatty diet, supplemented with various levels of black soy.

The results showed that, after two weeks, those getting 10 percent of their energy from black soy had gained half as much weight as those in the control group. Total blood cholesterol fell by 25 percent and LDL (so-called 'bad') cholesterol fell by 60 percent in the rats in the 10 percent group.

David Bender, sub-dean at the Royal Free and University College Medical School, London, thinks that the soya protein may be having an effect on fat metabolism in the liver and adipose tissue, reducing synthesis of new fatty acids and cholesterol. It is this metabolic effect that may explain the traditional Asian use of black soya in the treatment of diabetes.

¡°The key problem in type II diabetes is impairment of insulin action, mainly as a result of excess abdominal adipose tissue - so loss of weight often improves glycemic control,¡± says Dr Bender.

"Soy fits in well to a healthy balanced diet which is important in preventing diabetes - low in fat, high in fiber and a good source of complex carbohydrates,¡± Lynne Garton, a registered dietitian and nutritionist and consultant to the Soya Protein Association, said.