A chemical switch that tells cells when to burn fat and when to store it has been discovered in mice, paving the way for new drugs that could one day be used to control obesity and cholesterol².

Scientists at the Salk Institute in La Jolla, California, have identified a receptor in mouse cells that supervises how fat is used in the body and influences the ease with which mice put on weight.

If a similar regulator exists in human beings, which is likely, it would be a promising³ target for drugs that stimulate⁴ the burning of fat to fight the developed world's growing obesity epidemic⁵. Genes⁶ that carry the blueprint⁷ for receptor, PPARd, could also help to explain why some people seem to eat what they like and remain thin, while others find that every extra calorie goes straight on to the waistline.

Experiments revealed that when PPARd was stimulated⁸, mice used up fat deposits and lost weight, while mice with low PPARd activity were prone⁹ to obesity.

Mice with a highly active version weighed about 20 per cent less than normal mice at birth, and 35 per cent less at the age of one. The active receptor also protected mice against obesity when fed a high-calorie and high-fat diet. The findings are published today in the journal Cell.