Australian scientists believe they may have discovered how to help people lose weight without cutting back on food.
Researchers in Melbourne found that by manipulating fat cells in mice they were able to speed up metabolism.
After removing a particular enzyme, scientists found the mice were able to eat the same amount as others but burn more calories and gain less weight.
The breakthrough could pave the way for fat-burning drugs and also help to combat diabetes.
The research found that mice in which the angiotensin converting enzyme (ACE) had been removed were, on average, 20% lighter than normal mice and had up to 60% less body fat.
All the evidence we have is that nothing works better than a healthy diet and increased physical activity, with or without weight loss drugs
Dr Ian Campbell
Because of their faster metabolisms, it also appeared they had less chance of developing diabetes because they processed sugar more quickly.
Drugs which impair the action of ACE in humans already exist, and are used to combat high blood pressure.
The latest research could help the development of weight loss pills.
The question is whether they will have the same slimming effect on people as they have done on mice.
Dr Ian Campbell, medical director of the charity Weight Concern, said the study was "interesting", but stressed the work had only been carried out in mice.
He also said that although ACE inhibitor drugs were widely used to treat high blood pressure, there was nothing to indicate that, even at high doses, they encouraged weight loss in humans.
In addition, although the drugs were generally safe, they did carry a risk of side effects, such as kidney damage.
Dr Campbell said: "The promise that one will be able to eat more and not gain weight is unlikely to be fulfilled.
"All the evidence we have is that nothing works better than a healthy diet and increased physical activity, with or without weight loss drugs."