Brain condition causes former obese people to gain weight again, says expert

Obesity may impair the brain’s ability to recognize feelings of fullness and be satisfied after eating fats and sugars, a new study has found.

What’s more, these brain changes can last even after people considered clinically obese have lost a significant amount of weight – possibly explaining why many people often regain the pounds they’ve lost.

“There was no sign of reversibility – the brains of people with obesity continued to lack the chemical responses that tell the body, ‘OK, you’ve had enough,’” said Dr. Caroline Apovian, professor of medicine at Harvard Medical School. and co-director of the Center for Weight Management and Wellness at Brigham and Women’s Hospital in Boston.

As clinically defined, people with obesity have a body mass index, or BMI, over 30, while those with normal weight have 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 United Kingdom, who was not involved in the new research.

“The way they designed their study gives more confidence in the findings, adding to previous research that has also found that obesity causes some changes in the brain,” she said.

Nutrients provided by feeding tube

The study, published on Monday (12) at Nature Metabolism was a controlled clinical trial in which 30 people considered clinically obese and 30 people of normal weight were fed sugar, carbohydrates (glucose), fats (lipids) or water (as a control).

Each nutrient group was fed directly into the stomach via 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 the 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 ate the same meal for dinner at home and did not eat again until the feeding tube was installed the next morning.

As sugars or fats entered the stomach through the tube, the researchers used functional magnetic resonance imaging and single-photon emission computed tomography to capture the brain’s response within 30 minutes.

“The MRI shows where neurons in the brain are using oxygen in response to the nutrient – that part of the brain lights up,” Farooqi said. “The other test measures dopamine, a hormone that’s part of the reward system, which is a signal to find something pleasurable, rewarding, and motivating and then want that thing.”

The researchers were interested in how fats and glucose would individually trigger various brain areas connected to the rewarding aspects of food. They wanted to know if this would be different in people with obesity compared to people of normal weight.

“We were especially interested in the corpus striatum, the part of the brain involved in the motivation to actually look for food and eat it,” Serlie said. Buried deep in the brain, the corpus striatum also plays a role in emotion and habit formation.

In people of normal weight, the study found that brain signals in the striatum decreased when sugars or fats were placed in the digestive system – evidence that the brain recognized that the body had been fed.

“This general reduction in brain activity makes sense because once the food is in the stomach, you don’t have to go get more food,” explained Serlie.

At the same time, dopamine levels rose in those of normal weight, signaling that the brain’s reward centers were also activated.

Different outcomes for the clinically obese

However, when the same nutrients were given through a feeding tube to people considered clinically obese, brain activity did not decrease and dopamine levels did not increase.

This was especially true when the food was lipids or fats. That finding was interesting, Farooqi said, because the higher the fat content, the more rewarding the food.

“This is why you really want a burger over broccoli, the fat in the burger biologically will give a better response in the brain.”

The study then asked people with obesity to lose 10% of their body weight in 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 did not reset the brain in people with obesity, Serlie said.

“Nothing changed – the brain still didn’t recognize fullness or feel satisfied,” she said. “Now, you might say three months isn’t enough time or they haven’t lost enough weight.

“But this finding may also explain why people successfully lose weight and gain all the weight back a few years later – the impact on the brain may not be as reversible as we’d like it to be.”

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 was regained.

More research is needed

Caution is needed in interpreting the findings, Serlie said, as much is unknown: “We don’t know when these profound changes in the brain happen during weight gain. When does the brain start to slip and lose sensory capacity?

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 “the genes are influencing our response in the brain to certain nutrients,” said Farooqi, who has studied the role of genes in weight. for years.

Much more research is needed to fully understand what obesity does to the brain and whether this 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 when they gain weight? Or are there things they’ve been eating while gaining weight, like ultra-processed foods, that have caused a change in the brain? All of that is possible and we really don’t know what it is,” Farooqi said.

Until science answers these questions, the study emphasizes, 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 very simplistic and false,” she said.

“I think it’s important for people struggling with obesity to know that a malfunctioning brain could be the reason they struggle with food intake,” Serlie said. “And I hope this information increases empathy for this fight.”