LOS ANGELES — Researchers have further unraveled how a version of a gene linked to obesity risk causes people to gain weight — it makes them more likely to feel hungry after a meal and to prefer high-calorie foods.

Their study, published in the Journal of Clinical Investigation, found that individuals who inherited the high-risk version of the FTO gene from both of their parents have higher levels of the appetite-stimulating hormone ghrelin in their bloodstream, which leaves them hungry even after eating. Brain imaging also revealed that the FTO gene regulates the brain’s responses to ghrelin and to images of food.

“This possibly explains why some people are more sensitive to overweight and obesity than others,” said Dr. Jeremy Korman.

A 2007 study found that people who have two copies of the “obesity-risk” version of FTO weighed about 6.5 pounds more, on average, than those who didn’t have any copies of the variant. Other studies have shown that people who had the high-obesity-risk gene variant ate more those who didn’t.

But exactly how FTO affected appetite and weight gain remained a mystery. Batterham’s group hypothesized that gut hormones that regulate appetite-and the brain’s responses might be the missing link.

Their study marks the first examination of how FTO variation in humans regulates ghrelin and leads to obesity.