A diet rich in black soya beans could help control weight, lower fat and cholesterol levels, and aid in the prevention of diabetes, reports Lisa Richards in Chemistry & Industry, the magazine of the SCI.

Yellow soya has already been hailed for its cholesterol lowering capabilities; this is one of the reasons why frozen food manufacturer Birds Eye has added the beans to its range. However, a team of Korean researchers has shown that black soya may be even more potent in rats, and also prevents weight gain (Journal of the Science of Food and Agriculture, February 2007 DOI: 10.1002/jsfa2808).

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

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