May 12, 2023 -- A new study into how the brains of lean and obese people respond to nutrients may explain why it’s difficult for people to lose weight and keep it off.
Researchers from Yale University infused sugar carbohydrates (glucose), fats (lipids), or water (as a control) directly into the stomachs of 28 people considered lean (as defined by body mass index) and 30 people classified as obese, then observed their brain activity with magnetic resonance imaging.
Bypassing the mouth put the focus on the gut-brain connection and showed how people responded without tasting or smelling the food, Mireille Serlie, MD, the lead author and a professor of endocrinology at Yale School of Medicine, told CNN.
Imaging showed that lean or normal-weight people had a slowdown in brain activity and an increase in the release of dopamine, a chemical that triggers feelings of "reward" from food. But the people considered to be obese showed no slowdown in brain activity and no release of dopamine, says the study published in Nature Metabolism.
Participants defined as obese were then enrolled in a 12-week weight-loss program. People who lost at least 10% of their body fat went through the stomach infusion and brain imaging again, but the weight loss didn’t change the way their brains responded.
“Nothing changed — the brain still did not recognize fullness or feel satisfied,” Serlie told CNN. “Now, you might say three months is not long enough, or they didn’t lose enough weight.
“But this finding might also explain why people lose weight successfully and then regain all the weight a few years later — the impact on the brain may not be as reversible as we would like it to be.”
