The trial, at the University of East Anglia in Norwich, eastern England, will test whether a natural compound found in cocoa, the main ingredient of chocolate, could cut the risk of heart disease among women with diabetes.

A Belgian confectionist has created the special chocolate bar containing high levels of flavonoids -- a plant compound that has been shown to reduce heart risk factors -- to be used in the experiment. Soy, another natural source of flavonoids, has also been added to the bar.

Participants, who must be postmenopausal women under the age of 70, will have their risk of heart disease tested on five occasions during the year to see whether change occurs.

"The hypothesis of this exciting study is that flavonoids may improve the level of protection against heart disease over and above that provided by conventional drugs," said Dr. Ketan Dhatariya, a consultant in diabetes at the Norfolk and Norwich University Hospital.