Lucky genes can help protect people with obesity from certain diseases, a new study suggests.
These people tend to have their fat stored under their skin rather than on their organs.
Scientists say the findings explain why some obese people remain relatively healthy, while others suffer from life-changing conditions like type 2 diabetes and heart disease.
While anyone with a body mass index (BMI) over 30 is considered obese, two people with the same BMI can have very different amounts of fat, and that fat can be distributed in different places throughout the body.
Fat stored under the skin, like a paunch or a double chin, is considered less harmful than fat stored around organs such as the liver and heart.
And according to researchers, the genes people are born with determine how and where this fat is stored.
Dr Hanieh Yaghootkar, a lecturer in biosciences at Brunel University London – who led the research, said: “Some people have unlucky fat genes, meaning they store higher levels of fat everywhere, including under the skin, liver and pancreas.
“That’s associated with a higher risk of diseases such as type 2 diabetes.
“Others are luckier and have genes that mean higher fat under the skin but lower liver fat and a lower risk of diseases like type 2 diabetes.”
Of the 37 diseases the team tested, 12 – including coronary artery disease, stroke and type 2 diabetes – were directly related to the genes which determine where the fat is stored.
The study also found that nine of the conditions could be said to be unrelated to this and were most likely a result of simply carrying too much weight, such as having deep vein thrombosis or arthritic knees.
But the researchers warn that regardless of where someone stores their fat, being obese is a serious hazard to a person’s health.
They also found some other diseases previously thought to be related to someone’s weight, such as Alzheimer’s, appear to be unconnected.
Dr Yaghootkar said: “To better prevent and measure risk of disease, it is important to understand if obesity is a casual risk factor and if it is causal, which consequences of it – be they metabolic, mechanical or psychological – are deriving the risk.
“Our results also provide evidence that everyone will benefit from losing their extra fat even if they are metabolically healthy.”
The researchers hope doctors will be able to use the study results to determine if they should be targeting the adverse effects of someone’s obesity, or be trying to get them to shed a few pounds.
Timothy Frayling, professor of human genetics at the University of Exeter, said: “For example, there are many treatments that can lower the high-fat levels in the blood and around the organs that do not affect the extra weight a person carries.
“In contrast, for other conditions, it may be more important to reduce the extra weight as much as, or more than, the damaging high sugar and fat levels in the blood.”
The study, published in the journal eLife and funded by Diabetes UK, used data from Finland’s FinnGen project and the UK Biobank database, which collected information from 500,000 individuals aged 37 to 73 between 2006 and 2010 from across the UK.