Four million people in Britain carry a ‘skinny gene’

They won’t find themselves very popular with the rest of the population.

But there are almost four million people in Britain who are unlikely to put on weight because of a ‘thinness gene’ that curbs their appetite.

Scientists at the University of Cambridge revealed earlier this year that there really are people who are naturally skinny and don’t have to watch their weight.

Now they have found a specific gene which they say is the most important in keeping people slender.

A lucky six per cent of the population have variations in this gene which halve their chances of becoming obese.

These people are about five and a half pounds skinnier on average than someone without the genetic quirk. They are also up to 50 per cent less likely to develop type 2 diabetes and coronary artery disease.

The findings could lead to new drugs which mimic the genetic variations, keeping a switch in the brain which tells us to stop eating turned on.

Professor Sadaf Farooqi, from the University of Cambridge, co-led a study into the MC4R gene, looking at almost half a million British people from the UK Biobank genetic database.

She said: ‘This study drives home the fact that genetics plays a major role in why some people are obese, and that some people are fortunate enough to have genes that protect them from obesity.

‘It doesn’t mean that we can’t influence our weight by watching what we eat, but it does mean the odds are stacked against some people and in favour of others.’ 

The MC4R gene is already notorious for its role in weight gain. About one in 100 people have a mutation which stops the gene working, and they are far more likely to be morbidly obese.

Only recently did scientists work out that it can also keep people thin, and this is the first time it has become clear how many people could benefit.

Researchers looked at the gene in 452,300 people, finding 61 slight differences to it which affect body weight. 

The best nine genetic variations slashed people’s odds of becoming obese, getting type 2 diabetes or coronary artery disease by up to 50 per cent.

The study found six per cent of people carried one of these nine genetic variations, which means almost four million people in the UK are likely to have them.

This lucky group of people have a better chance of staying thin probably because they eat less than everyone else.

Their genetic quirk works by ‘switching on’ the MC4R gene, which controls the receptors on the surface of brain cells that tell us we are full and to stop eating.

These receptors normally stop working between meals, being reabsorbed into the cell. But people with the right genetic quirk have receptors which carry on working, keeping the ‘stop eating’ signal going for longer so people are less likely to overeat or snack between meals.

Slimming drugs to target the MC4R gene have previously had unwanted side effects. 

They have either given people high blood pressure, which the gene also controls, or changed their skin pigment which makes freckles much darker.

The new findings, published in the journal Cell, are hoped to lead to better drugs which use a biological pathway only now discovered by the researchers.

That could allow people who do not have the best version of the ‘thinness gene’ to get the same benefits.