It's not only healthy food and exercise, but skinny genes that hold the key 'to staying slim', say researchers who found that slim people have a genetic advantage when it comes to maintaining their weight.
The study, led by University of Cambridge researchers, looked at why some people manage to stay thin while others easily gain weight.
They found that thin people had a much lower genetic risk score -- they had fewer genetic variants that we know increase a person's chances of being overweight.
"This research shows for the first time that healthy thin people are generally thin because they have a lower burden of genes that increase a person's chances of being overweight and not because they are morally superior, as some people like to suggest," said Professor Sadaf Farooqi from the varsity.
"It's easy to rush to judgement and criticise people for their weight, but the science shows that things are far more complex. We have far less control over our weight than we might wish to think," he added.
In the study, published in the journal PLOS Genetics, the researchers compared the DNA of some 14,000 people -- 1,622 thin volunteers, 1,985 severely obese people and 10,433 normal weight controls.
Three out of four people had a family history of being thin and healthy and the team found some genetic changes that were significantly more common in thin people, which they say may allow them to pinpoint new genes and biological mechanisms that help people stay thin.
To see what impact these genes had on an individual's weight, the researchers added up the contribution of the different genetic variants to calculate a genetic risk score.
"As anticipated, we found that obese people had a higher genetic risk score than normal weight people, which contributes to their risk of being overweight. The genetic dice are loaded against them," explained Ines Barroso's from the Wellcome Sanger Institute.
"If we can find the genes that prevent them from putting on weight, we may be able to target those genes to find new weight loss strategies and help people who do not have this advantage," Farooqi added.