Scientists believe that they have found a clear genetic link to obesity, providing emotional relief for thousands of patients who lead a healthy lifestyle yet fail to lose weight.
A British study involving 38,000 people has revealed that one sixth of the population carry a variant of the FTO gene, which is believed to be an important factor in obesity.
According to the research, people with two copies of the gene carry around a 70 per cent higher risk of being obese and are on average three kilograms heavier than those with no copies.
Professor Andrew Hattersley, lead researcher from the Peninsular Medical School, commented: "Our findings suggest a possible answer to someone who might ask, 'I eat the same and do as much exercise as my friend next door, so why am I fatter'.
"There is clearly a component to obesity that is genetic."
Around one fifth of England's adult population are obese and this figure is expected to rise to a third of all men and 28 per cent of women by 2010, according to Department of Health figures.
Some patients are now being offered obesity surgery on the NHS to help them lose weight, but many seek private surgery to avoid lengthy waiting lists.
Independent advice on private healthcare