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Obesity may damage the brain’s ability to recognize feelings of fullness and fullness after eating fats and sugars, a new study has found.
Additionally, these brain changes can last even after people considered medically obese lose a significant amount of weight – perhaps explaining why many people often regain THE pounds they lose.
“There were no signs of reversibility – the brains of obese people still lacked the chemical responses that tell the body, ‘OK, you’ve eaten enough,'” said Dr Caroline Apovian, professor of medicine at Harvard Medical School and co-director. from the Center for Weight Management and Wellness at Brigham and Women’s Hospital in Boston.
According to the medical definition, obese people have a body mass index or BMIgreater than 30, while normal weight corresponds to a BMI between 18 and 25.
This study shows why obesity is a disease — there are real changes in the brain,” said Apovian, who was not involved in the study.
“The study is very rigorous and quite comprehensive,” said Dr I. Sadaf Farooqi, 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 gives more confidence in the results, adding to previous research who also discovered that obesity causes changes in the brain,” she said.
The study, published 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), fats (lipids), or water (as a control). Each nutrient group was introduced directly into the stomach via a feeding tube on different days.
“We wanted to bypass the mouth and focus on the gut-brain connection, to see how nutrients affect the brain independent of sight, smell or taste of food,” said the lead author. study, Dr. Mireille Serlie, professor of endocrinology at the Yale School of Medicine. in New Haven, Connecticut.
The day before the test, all 60 study participants ate the same meal for dinner at home and ate no more until the feeding tube was in place the next morning. When sugars or fats entered the stomach through the 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 neurons in the brain are using oxygen in response to the nutrient – that part of the brain is turning on,” Faroof said. “The other scan measures dopamine, a hormone that’s part of the reward system, which is a signal to find something enjoyable, rewarding, and motivating, and then to want that thing.”
The researchers were interested in how fats and glucose would individually trigger vdifferent areas of the brain related to the rewarding aspects of food. They wanted to know if it would be different in obese people compared to those of normal weight.
“We were particularly interested in the striatum, the part of the brain involved in motivation to seek out food and eat it,” Serlie said. Buried deep in the brain, the striatum also plays a role in forming emotions and habits.
In people of normal weight, the study found that brain signals in the striatum slowed when sugars or fats were introduced to the digestive system – evidence that the brain recognized that the body had been fed.
“This overall reduction in brain activity makes sense because once the food is in your stomach, you don’t need to reach for more food,” Serlie explained.
At the same time, dopamine levels increased in normal-weight people, signaling that reward centers in the brain were also activated.
However, when the same nutrients were given by feeding tube to people considered medically obese, brain activity did not slow down and dopamine levels did not increase.
This was especially true when the food consisted of lipids or fats. This finding was interesting, said Farooqi, because the higher the fat content, the more rewarding the food: “That’s why you really want a burger instead of broccoli, the fat in the burger will biologically give a better response in 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 sugar, reset metabolism and improve overall health, Serlie said.
The tests were repeated as before – with surprising results. Losing weight does not have reset the brain in obese people, Serlie said.
“Nothing changed – the brain still didn’t recognize fullness or feel unfulfilled,” she said. “Now you could say three months isn’t long enough, or they haven’t lost enough weight.
“But this finding could also explain why people successfully lose weight and then regain all the weight a few years later – the impact on the brain may not be as reversible as we would like.”
A Meta-analysis 2018 long-term clinical weight loss trials found that 50% of a person’s initial weight loss was recovered after two years – by year five, 80% of the weight had been recovered.
Care must be taken in interpreting the results, Serlie said, because much is unknown: “We don’t know when these profound changes in the brain occur during weight gain. When does the brain start to slip and lose the ability to sense? »
Obesity has a genetic component, and although the study tried to control for this by excluding people with childhood obesity, it’s still possible that “genes influence our response in the brain to certain nutrients,” said Farooqi, who has studied the role of genes on weight for years.
Much more research is needed to fully understand what obesity does to the brain, and whether it is triggered by the fatty tissue itself, the types of foods eaten, or other environmental and genetic factors.
“Are there any changes that have happened to people as they gained weight? Or are there things they ate while they were gaining weight, like ultra-processed foods, that caused a change in the brain? It’s all possible, and we don’t really know what it is,” Farooqi said.
Until science answers these questions, the study highlights, once again, that weight stigma has no place in the fight against obesity, Serlie said.
“The belief that weight gain can be solved simply by ‘eating less, exercising more and if you don’t it’s a lack of willpower is so simplistic and so wrong,” he said. she declared.
“I think it’s important for people struggling with obesity to know that a faulty brain may be the reason they struggle with food intake,” Serlie said. “And hopefully this information will increase empathy for this struggle.”
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