CNN
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Obesity may impair the brain’s ability to recognize feelings of fullness and satisfaction after eating fats and sugars, a new study finds.
Plus, those brain changes can last even after people considered medically obese lose a significant amount of weight — possibly explains why many people often recovers The they lose pounds.
“There’s no sign of reversibility — the brains of obese people continue to lack the chemical responses that tell the body, ‘OK, eat enough,'” said Dr. Caroline Apovian, a professor of medicine at Harvard Medical School and codirector of the Center for Weight Management and Wellness at Brigham and Women’s Hospital in Boston.
As defined medically, people with obesity have a body mass index, or BMIwhich is over 30, while normal weight is a BMI between 18 and 25.
“This study captures why obesity is a disease — there are actual changes in the brain,” said Apovian, who was not involved in the study.
“The study was very rigorous and quite comprehensive,” said Dr. I. Sadaf Farooqi, a professor of metabolism and medicine at the University of Cambridge in the UK, who was not involved in the new research.
“The way they designed their study lends more confidence to the findings, adding to previous research that also found obesity causes some changes in the brain,” he said.
The studying, published on Monday in Nature Metabolism, was a controlled clinical trial in which 30 people considered medically obese and 30 people of normal weight were fed sugary carbohydrates (glucose), fat (lipids) or water (as a control). Each group of nutrients was fed directly into the stomach through a feeding tube on separate days.
“We wanted to bypass the mouth and focus on the gut-brain connection, to see how nutrients affect the brain independently of seeing, smelling or tasting food,” said lead study author Dr. Mireille Serlie, professor of endocrinology at the Yale School of Medicine in New Haven, Connecticut.
The night before the test, all 60 study participants had the same meal for dinner at home and did not eat again until the feeding tube was in place the next morning. While either sugar or fat entered the stomach through a tube, the researchers used functional magnetic resonance imaging (fMRI) and single-photon emission computed tomography (SPECT) to capture the brain’s response for 30 minutes. .
“The MRI shows where the neurons in the brain are using oxygen in reaction to the nutrient — that part of the brain lights up,” Farooqi said. “Other scans measure dopamine, a hormone that is part of the reward system, which is a signal for finding something pleasurable, rewarding and motivating and then wanting that thing.”
Researchers are interested in how fat and glucose individually trigger vdifferent parts of the brain connected with the rewarding aspects of food. They wanted to know if it would be different in people who were obese compared to people of normal weight.
“We were particularly interested in the striatum, the part of the brain involved in the motivation to actually go and find food and eat it,” Serlie said. Embedded deep in the brain, the striatum also plays a role in the development of emotion and behavior.
In people of normal weight, the study found that brain signals in the striatum slowed down when either sugars or fats were put into the digestive system – evidence that the brain recognized that the body had been fed.
“The overall reduction in brain activity makes sense because when the food is in your stomach, you don’t have to go and get more food,” explains Serlie.
At the same time, dopamine levels increased in those of normal weight, indicating that the brain’s reward centers were also activated.
However, when the same nutrients were given through a feeding tube to people considered medically obese, brain activity did not slow, and dopamine levels did not increase.
This is especially true when the food is lipids or fats. That finding is interesting, Farooqi said, because the higher the fat content, the more beneficial the food: “That’s why you really want a burger instead of broccoli, the fat in the burger is biologically which will give a better response to the brain.”
Next, the study asked obese people to lose 10% of their body weight over three months – an amount of weight known to improve blood sugars, reset metabolism and boost overall health, says Serlie.
The tests were repeated as before — with surprising results. Weight loss is not reset the brain in people with obesity, Serlie said.
“Nothing has changed – the brain still doesn’t recognize fullness or satisfaction,” he said. “Now, you can say that three months is not enough, or they didn’t lose enough weight.
“But this finding may also explain why people lose weight successfully and then regain all the weight years later – the effect on the brain may not be as reversible as we would like.”
A 2018 meta-analysis of long-term weight loss clinical trials found that 50% of a person’s original weight loss was regained after two years — by the fifth year, 80% of the weight had been regained.
Caution is needed in interpreting the findings, says Serlie, as it is unknown: “We don’t know when these profound changes in the brain occur during weight gain. When does the brain begin to slip and lose its cognitive capacity?”
Obesity has a genetic component, and even though the study tried to control for that by excluding people with early-onset obesity, it’s still possible that “genes influence our brain response to some nutrients,” says Farooqi, who has The role of genes in weight has been studied for many years.
More research is needed to fully understand what obesity does to the brain, and whether that is triggered by the fat tissue itself, the types of food eaten, or other environmental and genetic factors.
“Are there changes that occur in people as they gain weight? Or are there things they eat as they gain weight, such as ultra-processed foods, that caused a change in the brain? All of these are possible, and we don’t really know which one it is,” said Farooqi.
Until science answers these questions, the study emphasizes, again, that weight stigma has no place in the fight against obesity, Serlie said.
“The belief that weight gain can be solved by simply ‘eating less, exercising more, and if you don’t do that, it’s a lack of willpower is very simplistic and false, ” he says.
“I think it’s important for people struggling with obesity to know that a dysfunctional brain may be the reason they’re struggling with food intake,” Serlie said. “And hopefully this information will increase empathy for that struggle.”
