According to Yale University researchers, obesity is linked to a reduced brain reaction to nutrient intake, which is persistent even after losing weight.
The study highlights the significant role of the human brain in obesity and provides insights into the reason why maintaining weight loss is difficult for some.
In the case of such people, following a meal, the gut sends a series of signals to the brain informing it that nutrients are present, and this phenomenon is thought to help control eating habits.
However, while the detection of nutrients in the stomach does cause changes in brain activity in thin individuals, such brain responses are primarily diminished in people with obesity, according to a study led by Yale’s Mireille Serlie.
According to the researchers, these discrepancies in brain activity may contribute to the reasons why it’s challenging for some people to lose weight and keep it off.
The research results were released on June 12 in Nature Metabolism.
The World Health Organization estimates that more than 4 million people die every year as a result of obesity, and researchers say that in order to combat its devastating effects on the world as a whole, it is imperative to understand the biological factors that contribute to it.
Furthermore, although the way the body reacts to nutrient intake may play a significant role in eating behavior, little is known about how nutrients signal in humans.
In the new study, 30 subjects with obesity and 28 participants who were classified as “overweight” had glucose or fat infused directly into their stomachs.
They next used fMRI to measure brain activity.
Following the injection of both glucose and fat, the researchers observed evidence of decreased activity across several brain regions in the lean participants. On the other hand, they noticed no changes in activity in the obese participants.
Serlie, a senior author of the study, said that “This was surprising. We thought there would be different responses between lean people and people with obesity, but we didn’t expect this lack of changes in brain activity in people with obesity.”
Then, Serlie and her coworkers focused on the striatum, a part of the brain that has been linked to mediating the motivating and rewarding aspects of food intake as well as being crucial in controlling eating behavior in previous studies.
The neurotransmitter dopamine assists the striatum in doing this in part.
They discovered using fMRI that in lean individuals, both glucose and fat resulted in a decrease in activity in two regions of the striatum.
However, only glucose, and only in one region of the striatum, caused changes in brain activity in the obese participants.
The activity of this area of the brain was unaffected by fat.
Dopamine release in the striatum after nutrient infusion was assessed by researchers, and they discovered that although fat only generated dopamine release in lean people, glucose caused dopamine release in both groups.
According to the researchers, these results are consistent with impaired nutritional sensing in obese individuals.
Following a 12-week nutritional weight-loss program, obese research participants underwent re-imaging after losing at least 10 percent of their body weight.
According to the study’s findings, in these people, losing weight had no impact on how the brain reacted to nutrition infusion. Serlie stated that none of the reduced reactions had been regained.
Prior research has shown that the majority of people who lose weight quickly gain it back after dieting.
According to the researchers, these new discoveries may contribute to explaining why that is so frequently the case.
Serlie stated that “In my clinic, when I see people with obesity, they often tell me, ‘I ate dinner. I know I did. But it doesn’t feel like it.’ And I think that’s part of this defective nutrient sensing. This may be why people overeat despite the fact that they’ve consumed enough calories. And, importantly, it might explain why it’s so hard to keep weight off.”
According to Serlie, more research is still needed to fully understand the biology of eating behavior in human beings.
This includes learning why reduced nutrition sensing happens in some, what biological pathways are involved, and when the changes start to take effect.
“Everyone overeats at times. But it’s unclear why some people continue to overeat and others don’t. We need to find where that point is when the brain starts to lose its capacity to regulate food intake and what determines that switch. Because if you know when and how it happens, you might be able to prevent it,” the expert shared.
Similarly to this, understanding when nutrient-sensing alterations become permanent will assist doctors in planning patient treatments.
And Serlie stated that one objective for the future would be to, if at all possible, figure out how to bring back nutrient sensing.
In any case, she claimed, the results highlight the crucial role played by the human brain in obesity.
“People still think obesity is caused by a lack of willpower. But we’ve shown that there is a real difference in the brain when it comes to nutrient sensing,” Serlie also stressed.
