SEATTLE - The Centers for Disease Control and Prevention estimates a third of American adults are obese, and another third are considered overweight. Now, a new study from the University of Washington may shed some light on why it's so hard to lose weight.

"The number of people losing weight or stating that they have tried to lose weight over the past year is 50%," said Dr. Ellen Schur, associate professor of medicine and the clinical research director at UW Medicine Diabetes Institute in Seattle.

Schur helps patients lose weight. She said weight loss itself causes hormone changes that make food more appealing, so it's harder to keep weight off. In another UW lab, Mark Rossi and Marcus Basiri's study shows that overeating changes brain cells that suppress food intake.

"We don't know the exact mechanisms that are contributing to it, but we see that there are profound changes across lots of different cell types," Rossi said.

"So these glutamate neurons, which normally function to suppress feeding, were kind of toning down their firing patterns," Basiri stated.

As the mice got fatter, neurons got worse at putting the brakes on eating. The team hopes this leads to new ways to treat obesity in people one day.

Now, the research team is working on isolating an even smaller set of cells that are affected by overeating. They haven't yet discovered whether the neurons can change back to how they worked before obesity.