The findings explain why the success of gastric bypass surgery varies so widely and could help clinicians identify those who would benefit the most from this type of surgery.
"Surgery is the most effective therapy for severe obesity, but these procedures are invasive, and not all patients get the same degree of benefit," senior study author Lee Kaplan of Massachusetts General Hospital and Harvard Medical School said.
"If we can identify those patients who are likely to lose more weight after surgery from those who do less well, we could help steer patients towards the therapy that best suits them," Kaplan said.
Individuals who undergo gastric bypass surgery lose on average about 35 percent to 40 percent of their initial weight and keep most of this weight off.
But the amount of weight lost by different patients varies by a factor of four, and it is not understood what causes this wide difference in response.
To identify specific genetic factors that might play a role, Kaplan and his team examined the genomes of more than 1,000 individuals undergoing gastric bypass surgery.
They found that individuals with two copies of a specific variant on chromosome 15 lost on average about 39 percent of their body weight, whereas those without a copy of this variant lost less than 30 percent of their body weight.
Moreover, the activity of the gene located closest to this variant also predicted weight loss.
The study is published in The American Journal of Human Genetics.