Looking at the different variants at this location, the researchers found that people with two copies of the more common variant lost an average of 39 percent of their starting weight, while the one person in the study who had two copies of the less common variant shed 29 percent of starting weight.
Patients with just a single copy of the less common DNA variant were 2.5 times more likely to lose less than 30 percent of their total bodyweight after surgery than patients without that variant.
Next, researchers checked the activity of the two genes closest to the location of the gene variant.
People with greater expression of the gene closest to the variant in their abdominal fat lost more weight after surgery than those with less gene activity there. That remained true even after researchers adjusted their results for factors such as age, sex, diabetes and body-mass index (a measure of body fat based on a person's ratio of height and weight) before surgery.
To check their results another way, they also looked at the activity of two genes closest to the variant in obese mice given either a gastric bypass or sham surgery. Ten months after the procedures, the gene expression in mice that had gastric bypass was different than in mice that had sham surgeries.
"There's an enormous amount of biology that's changed in response to the surgery," said Dr. Lee Kaplan, director of the Obesity, Metabolism, & Nutrition Institute at Massachusetts General Hospital, in Boston.
Doctors once thought patients lost weight after gastric bypass simply because their stomachs were smaller, allowing them to feel full after eating a lot less.
But recent studies have shown the surgery also alters hormones, gut microbes and the activity of genes.
"That's probably why surgery is so effective clinically, bec
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