'We have far less control over our weight than we might wish to think,” the study author noted. VGstockstudio/Shutterstock

We all have a friend who seems to eat and eat and eat without putting on a single pound. Unfortunately for those hoping to learn this trick, it seems as if this quirk is deeply embedded in our DNA.

New research, published in the open-access journal PLOS Genetics, set out to find the “genetic architecture” of skinniness and severe obesity in the “largest study of its kind to date”. Their findings highlight several new genetic variants that are widely associated with severe obesity and others linked to “healthy thinness”, which can help explain why some people find it easier to stay slim than others.

Much of the focus on the so-called obesity epidemic is on environmental factors, such as calorific diets or lazy lifestyles – and rightly so. However, as this study shows, genetics can also play a decisive factor.

In short, obesity is a more complex situation than just eating too many burgers.

“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,” study leader Professor Sadaf Farooqi said in a statement. “It’s easy to rush to judgment and criticize 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."

Researchers led by the University of Cambridge in the UK looked at the DNA of some 14,000 people – 1,622 thin people, 1,985 severely obese people, and 10,433 people with an average body mass index (BMI). After identifying the genes that appeared to be linked to slimmer people, they then worked out a genetic risk score for each person.

“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,” added researcher Dr Inês Barroso of the Wellcome Sanger Institute.

It’s unclear yet how these genetic variants can dictate weight gain, although a number of previous studies have suggested it’s a matter of metabolism.

Obesity is a growing problem in many parts of the world. Over 93 million people, almost 40 percent of the population, in the US are classified as being obese – and that figure is continuing to rise. In the UK, that figure is around one in four. The researchers hope that their study will help to get a more nuanced understanding of the obesity epidemic and fine-tune some new weight loss strategies.

Professor Farooqi added: "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.”