'Energy-burning' gene holds obesity clues

Obesity is a growing health problem in the West

A gene which helps the body burn off excessive energy may help doctors come up with a treatment for obesity.

It may also help in the control of adult-onset diabetes - one of the most common illnesses in older people.

Experts from the Washington School of Medicine, US, were able to overfeed genetically altered mice without the rodents putting on weight.

Their findings are published in the journal Nature Medicine and although the results may not be easily reproduced in humans, they offer strong evidence for the role of the gene.

The gene in question controls a body chemical called "uncoupling protein one" (UCP1).

This is found in the membrane of cell structures called mitochondria.

The mitochondria are often referred to as the cell's "power stations", and one of their key roles is to convert food energy from carbohydrates into the chemical energy required to run the body.

Eating like mice

The body must employ a delicate balancing act: if too much chemical energy is made, it cannot all be used and the excess will be laid down as fat.

The more calories of food energy eaten, the harder it is for the body maintain the balance.

The UCP1 gene is vital to that balancing. When the gene is switched on, the excess energy is released as simple heat rather than turned into the chemical energy that might end up as fat.

The researchers found a method for turning on the UCP1 in the "brown fat" of mice, which were smaller despite eating the same amount of food as other rodents.

Even altered mice fed a high-fat "Western" diet managed not to pile on weight.

Professor Mark McCarthy is an expert in genomic medicine at Imperial College, London, and is studying the function of UCP genes in humans. He has found that variations in the gene occur in overweight people.

But he said that while it was quite possible the human UCP genes had the same role as in mice, this was not proven.

Strong effects

Although UCP1 was the gene with the biggest effect, he said, humans had little of the tissue containing it.

He said: "Humans don't have as much 'brown fat' as these mice, but there is another gene called UCP3 which is found in skeletal muscle, of which we have a great deal.

"We might be able to find a way to switch that on all the time, although the effect of UCP3 is not as strong as that of UCP1."

However, he said that even if a UCP gene could be harnessed, there might be other body systems that would adapt to stop the weight coming off.

"We all know what a struggle it is to lose weight," he said.

Obesity is one of the greatest health challenges for modern Western societies, as it contributes to the development of diabetes and heart disease. Even childhood obesity in the US currently runs at approximately 30%.