While anyone with a BMI of 30 or higher is considered obese, two people with the same BMI can have very different amounts of fat, and that fat can be distributed differently throughout the body. Geneticists have discovered why some people with obesity are relatively healthy, while others suffer from life-changing illnesses like type 2 diabetes and heart disease.
Anyone with a BMI greater than 30 is considered obese rather than overweight, and while people with obesity all have a few extra kilos in common, two people with the same BMI can have very different amounts of fat, and that fat can be distributed differently throughout the body. Fat stored beneath the skin, such as a paunch or a double chin, is thought to be less harmful than fat stored around organs such as the liver and heart, and the genes we inherit determine how and where this fat is stored – what scientists refer to as having ‘favourable’ or ‘unfavourable’ adiposity.
Fat stored beneath the skin, such as a tummy tuck or a double chin, is thought to be less harmful than fat stored around organs such as the liver and heart. Researchers believe that the genes people are born with determine how and where this fat is stored. Those who have the lucky genes have their fat stored under the skin rather than on their organs, which reduces the risk of certain diseases.
To better prevent and measure disease risk, it is critical to understand whether obesity is a causal risk factor and, if so, which consequences of obesity whether metabolic, mechanical, or psychological are deriving the risk.
Dr. Yaghootkar
“Some people have unlucky fat genes, which cause them to store more fat everywhere, including under the skin, liver, and pancreas. This is linked to an increased risk of diseases such as type 2 diabetes” Dr. Hanieh Yaghootkar, a lecturer in biosciences at Brunel University London, led the study. “Others are luckier in that they have genes that indicate higher fat under the skin but lower liver fat and a lower risk of diseases such as type 2 diabetes.”
Using a technique known as Mendelian randomisation, the researchers discovered that 12 of the 37 diseases tested, including coronary artery disease, stroke, and type 2 diabetes, were directly related to the genes that determine whether or not a person has a ‘favourable adiposity,’ while the remaining nine were unrelated to adiposity and were most likely caused by simply carrying too much weight, such as having deep vein thrombosis or arthritic knees.
However, the researchers warn that being obese is a serious health risk regardless of whether someone has a favourable or unfavourable adiposity, with even those with a favourable adiposity at a heightened risk of diseases such as gallstones, adult-onset asthma, and psoriasis.
They also discovered that some diseases previously thought to be linked to a person’s weight, such as Alzheimer’s, appear to be unrelated.
“To better prevent and measure disease risk, it is critical to understand whether obesity is a causal risk factor and, if so, which consequences of obesity — whether metabolic, mechanical, or psychological — are deriving the risk,” said Dr. Yaghootkar. “Our results also provide evidence that everyone will benefit from losing their excess fat, even if they are metabolically healthy,” she added.
The findings, according to the researchers, will help doctors decide whether to target the negative effects of someone’s obesity or try to get them to lose a few pounds. “For example, there are many treatments that can lower high-fat levels in the blood and around the organs without affecting the extra weight a person carries,” Prof Timothy Frayling, Professor of Human Genetics at the University of Exeter, explained.
“In contrast, for other conditions, it may be more important to lose weight as much as, if not more than, the harmful high sugar and fat levels in the blood.”
The study, which was funded by Diabetes UK and conducted in collaboration with the University of Winchester, used data from Finland’s FinnGen project and the UK Biobank, which collected information from 500,000 people aged 37 to 73 from across the UK between 2006 and 2010. The NHS already considers one in every four people to be “very overweight” and at high risk of becoming seriously ill.
Dr. Susan Martin, an Exeter postdoctoral research fellow who was involved in the study, stated: “While it is critical to identify the causes of obesity-related disease, good genes are not a replacement for a healthy lifestyle. A favorable adiposity will only get you so far; if you’re obese, you should still try to shift the excess weight wherever you can.”
