New study shows brain changes could be a reason it's hard to lose weight
Experts say how the brain responds to food may be a key factor.
Ways to lose weight have been trending with the rising popularity and success stories of certain drugs that help with weight loss, such as Ozempic and Mounjaro, and more people turning to supplements like berberine, deemed "nature's Ozempic."
Still, many people who have obesity report struggling to sustain weight loss.
Now, new research shows that it's not just about willpower to lose weight and keep it off: Experts say how your brain responds to food may make a big difference.
A recent study published in Nature Metabolism found that the brain responds to nutrients differently in people who have obesity, even after meaningful weight loss.
Researchers studied 60 participants over 40 years old; half had a diagnosis of obesity and half did not.
To understand how the brain responds to food in these two groups, different solutions containing glucose, lipids or water alone were directly infused into participants' stomachs on separate days. Brain responses were then measured with functional MRI scans for about 30 minutes post-infusion, and researchers also measured hormonal levels in the blood and participant-reported hunger scores.
The results showed that the group of participants without obesity had appropriate activation of reward centers in the brain in response to the nutrients.
Conversely, these same areas of the brain were not activated on the scan for participants with obesity.
This finding did not change after repeating the scan three months later in participants with obesity who experienced 10% diet-driven weight loss.
Experts say this lack of reward response could lead to overeating and make it difficult to change eating habits that can contribute to weight gain.
"This study really, really proves the biological and brain causes are contributions for overweight and obesity are really a real thing," said Dr. Jennifer Ashton, ABC News chief medical correspondent and board-certified obesity medicine specialist.
While these findings further support what experts know to be true, that there's more behind weight loss than willpower, researchers in the study caution there are important limitations.
It was only done in a relatively few number of adults over 40 years old, so it may not be generalizable to younger populations. And the study used a feeding tube to give the nutrients that doesn't mimic how most people really eat or account for food choices, so these differences in the brain may not hold true in all circumstances.
Experts also emphasize that these findings do not guarantee someone with obesity can't lose weight and keep that weight off even in the setting of these changes. Ashton adds that she hopes studies like this one fuel more targeted treatments for people who are overweight or have obesity, and add to evidence supporting why medications that are used for weight loss, like Wegovy, are proving to work so well for some people.
"I think it represents a possibility for target and intervention starting in the brain with those hormonal signals of hunger and satiety, and that's what a lot of these FDA-approved weight loss drugs are doing," Ashton said.
Dr. Jade A Cobern, M.D., M.P.H., board-eligible in pediatrics and resident in General Preventive Medicine at Johns Hopkins, is a member of the ABC News Medical Unit.