Your thin friends can scarf down carbs? It may be their genes

dna strand

No big surprise, but a new genetic study has confirmed why some people can eat whatever they like and still stay thin. It is not because they have better will power. It’s because they inherited lucky genes.

In the world’s largest genome-wide association study of the inheritability of body weight to date, researchers from the UK and the US compared the genomes of 1,622 naturally thin people, 1,985 severely obese people and 10,433 normal controls.

The thin individuals all had BMIs less than 18 — which is considered underweight — but were healthy with no eating disorders or other medical conditions. The study, called STILTS (Study Into Lean and Thin Subjects) wondered whether there would be any genetic overlap between the genes found for obesity or thinness.

PLOS Genetics: Genetic architecture of human thinness compared to severe obesity

Many previous studies have shown a strong genetic susceptibility to obesity, with currently more than 250 genes already identified. The authors note, however, that much less is known about the specific genetic characteristics of persistently thin people. Did they share some of the same genes but in essence inherit the flip side of the coin? Did they have different genes not found in those with obesity that conferred an advantage?

The study, indeed, found several common gene variants were shared between the severe obesity and extremely thin but also found new genes for both. Adding up all the various genes, investigators were able to create a genetic risk score for obesity. Little wonder, extremely thin people were found to have a lower genetic risk score. Indeed, of the thin people they recruited for the study, the majority had thin parents and relatives.

The researchers say their results may someday help pinpoint anti-obesity strategies or medications to target the action of specific genes.

Science Daily: Thin people have a genetic advantage when it comes to maintaining their weight

Newsweek: Why do thin people not get fat? They got lucky with their genes

Technology Networks: Can’t fit in your jeans? It may be your genes

The Guardian: Thinness and obesity – it’s in the genes

How does genetic information like this help readers who may be struggling with their weight? If you inherited genes that increase your risk for obesity, is there simply nothing you can do?

Not at all. There is a common saying in genetics: “Genes load the gun, but environment pulls the trigger.” And we know, without a doubt, that the food environment has changed drastically these past four decades to a low-fat, high-carb world that is associated with the obesity epidemic and may have put some people at a genetic disadvantage. That time frame is far too short to actually change inherited genes, but is enough time to change gene expression — to pull the trigger, in essence.

While individuals with genes for thinness may have no need to watch what they eat or cut their carb intake to remain thin in this new carb-rich environment, it may be extremely effective for those with an increased risk for obesity to pay close attention to their food choices. And remember, weight is not an ideal measure of health, so even thin individuals need to pay attention to metabolic and other markers of health that may be compromised by a diet rich in processed carbs.

The science backs this up. As we reported in late 2018, children and teens with a genetic propensity for obesity were able to lose weight just as well as their overweight peers who did not inherit a propensity to become obese.

Anne Mullens


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