Scientists discover a SECOND fat gene - rogue DNA carried by one third of the population

They pinpointed a stretch of rogue DNA that is carried by more than a third of the population and increases the chances of becoming fat.

Its effects however are compounded by the presence of the FTO gene - which, when discovered last year, was the first widespread gene known to affect obesity.

The find could help explain why some seem to effortlessly lose weight - and others wage a constant fight.

Researcher Dr Innes Barroso said: "Genetic variants like this one partly help to explain why some people find it harder than others to maintain a normal weight.

"It is really important people understand there is a genetic predisposition to obesity and that might help people to be less prejudiced towards the obese."

Unravelling the genetics of obesity could also pave the way for treatments for the condition.

The researchers, from 77 institutions in six countries including the UK, analysed the DNA of 90,000 individuals.

As genetic sequences come in pairs, the effect is greatest in those with two flawed copies.

These adults - roughly one in 17 Britons - are around three and a half pounds heavier than those lacking the flaw and 24 per cent more likely to be obese than others.

Around 37 per cent carry one copy - and are 12 per cent more likely to be obese.

However, the unlucky few who have two copies of the newly-discovered DNA - and two flawed copies of FTO - tend to be more than half a stone heavier than those without such an inheritance.

It is thought the flaw affects the ability of another gene to regulate appetite and energy expenditure, journal Nature Genetics reports.

A separate study led by Imperial College London found DNA carried by half of us increases waist circumference by just under an inch.