Scientists may have found the Holy Grail of weight control in a protein that allows you to eat more but remain thin.
So far it only works on mice but the researchers, from SmithKline Beecham Pharmaceuticals and the University of Cambridge, believe the discovery could lead the way towards new treatments for human obesity.
The human protein, uncoupling protein 3 (UCP-3), was genetically engineered into mice, after which they were found to be able to eat more than normal mice, yet remain leaner and lighter. The work is described in the science journal, Nature.
The mice overexpress UCP-3 in the mitochondria of their muscle tissues. Mitochondria release the energy locked in food to make the chemical fuel used by the body, ATP. Some amount of UCP-3 is usually present but when it is increased, the body burns off energy without making ATP. Instead, the energy is converted directly to heat.
The engineered mice were given 50 per cent more food but weighed no more than their littermates.
They also consumed between 77 per cent and 91 per cent more oxygen but this higher energy use was not matched by extra "locomotor activity". Muscle temperature increased, but the core body temperature of the animals was not affected by the insertion of the transgene.
The research team stated that while some human studies had demonstrated a role for UCP-3 in the control of energy expenditure, others had failed to make this connection.
However, they added that there were no such contradictions in these particular experiments. The mice that overexpressed the protein stayed lighter, stored less fat and made more effective use of insulin, which controls sugar levels in the blood.