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


Don’t blame your parents! Kids can overcome genetic susceptibility for obesity

Not all adipose (fat tissue) is created equal

Global obesity report: Big food should lose its seat at the table

Weight loss


  1. Lisa
    Give it long enough time and that diet induced inflammation will be detrimental. Just because someone is pain free doesn't mean healthy.
  2. Jill
    I was a naturally skinny girl, ate everything in sight, sugar all day long, stayed super skinny for years, bmi under 18, etc. And after years of desk sitting jobs and eating obscene amounts of food and obscene amounts of sugar, maybe 7000-10,000 a day, my "genetically' fast metabolism is long gone. So, I don't believe that anyone can eat crazy amounts of carbs and stay skinny forever. If anyone could, it would have been me. But I have ended up very heavy, obese actually, prediabetic with insulin resistance. And I am severely sugar addicted, so I have been unable to reverse it yet. Once you have destroyed your body's ability to use sugar or insulin or however it works (from gorging on sugar for so long), your fast metabolism will be a thing of the past, regardless of your genetics or original metabolism.
    Reply: #5
  3. Joan
    I have such a low metabolism I can look at good and gain weight. Although not obese but am overweight and can't lose much even if I starve myself or eat healthy
  4. Geoff
    I’m a Primal Health Coach, CrossFit Coach, KettleBell Coach, I see every diet out there: Renaissance Periodization (RP) is the latest craze with CrossFit athletes which is 4-6 meals thru the waking day with anywhere from 150-300 grams carbohydrate of which a fair dose is from processed athlete supplements. I understand how these athletes initially lose body fat (all diets work at first) or not put on too much fat because of the cronic crazy workouts normal people will not do. They too cycle on/off the RP Diet with a lean out phase. Most of these athletes are under 40 years of age. Above 40, I do see some body fat increase. The BIG QUESTION is: What is happening metabolically? Fat/shinny genes aside, what about the high insulin reaction?
  5. Amanda
    I do love it when people use themselves as an example to generalise out. How do you even know you had those genes to begin with?
  6. Tee Dee
    It may be a metabolic advantage for staying thin, but it's apparently an evolutionary disadvantage to be unable to gain much fat. Fat protected our ancestors through harsh winters with lower food intake. It's sometimes little comfort when trying to lose weight, but I now see my 'ability' to store fat as an advantage if things ever get to the "Mad Max" stage in our future ;-)
  7. Kari
    where in the study is outlined that they can eat whatever the like ?
    I dont see any information about eating more than obese subj.

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