Obesity irreversibly alters the brain – 06/13/2023 – Equilibrium

In a study with 60 participants, those obese were unable to record satiety – and remained so, even after losing weight. A sign that the disease is not treated with “less food, more exercise” and stigmatization.

Obesity can impair the ability of the human brain to recognize the feeling of satiety and to be satisfied after eating fats and sugars, indicates an article published on Monday (12) by the scientific journal Nature Metabolism. There are signs that these changes are irreversible, even after 10% weight loss.

In a controlled study, 30 clinically obese and 30 normal-weight individuals were given glucose, lipids and water (as a control element) directly into the stomach through a tube. A person with a BMI (body mass index) greater than 30 is considered clinically obese. The normal rate is between 18 and 25.

“We wanted to go beyond the mouth and focus on the stomach-brain connection to see how nutrients affect the brain, regardless of whether you see, smell or taste the food,” lead author Mireille Serlie, a professor of of Endocrinology at the Yale School of Medicine in New Haven, Connecticut (USA).

Brain reactions vary with BMI

The night before the test, all 60 participants ate the same meal at home, and did not eat anything else until the feeding tube was inserted the next morning.

As sugars or fats entered the stomach, the researchers used functional magnetic resonance imaging and single-photon emission computed tomography (Spect) to record the brain’s reaction over the course of 30 minutes.

The objective was to verify how lipids and glucose would individually activate different brain areas related to the rewarding aspects of food, in search of possible differences between the two groups of participants.

“We were especially interested in the corpus striatum, the part of the brain involved in the motivation to actively seek out and eat food,” Serlie reports. Situated deep within the brain, the region also plays a role in emotions and habit formation.

“The MRI [ressonância magnética] shows where the neurons are consuming oxygen in reaction to the nutrient: that part of the brain lights up,” Sadaf Farooqi, professor of metabolism and medicine at the University of Cambridge, who was not part of the research, told CNN.

“The other track measures dopamine, a hormone that makes up the reward system, the signal to find something pleasurable, gratifying and motivating, and then wanting that thing.”

Brain is not as flexible as you would like

In subjects of normal weight, the electrical signals from the striatum slowed down when sugars or fats were introduced into the digestive system, indicating that the brain recognized that the organism had been fed.

That makes sense, because “once the food gets to the stomach, there’s no point in getting more food,” says Serlie. At the same time, dopamine levels rose, signaling that the reward centers had also been activated.

This was not the case with the clinically obese group, but their overall brain activity did not slow down, and their dopamine levels did not drop.

Obese participants were then asked to lose 10% of their weight within three months – a percentage that has been shown to improve blood glucose levels, reset metabolism and benefit overall health.

When the tests were repeated, the surprise was that the brain response of these individuals had not readapted. “Nothing changed: your brain still didn’t register satiety or feeling full,” reports Serlie.

“Well, it could be argued that three months is not enough time, or that they didn’t lose enough weight. But this result perhaps also explains why some people manage to lose weight and then gain it all back a few years later: the impact on the brain is perhaps not as reversible as we would like it to be.”

A meta-analysis of long-term weight loss clinical trials conducted in 2018 found that 50% of weight was regained after two years. Until the fifth year, the average rate was 80%.

Obesity is considered a disease

Sadaf Farooqi calls the US experiment “very rigorous and very comprehensive”. Its relevance is confirmed by another CNN interviewee, Caroline M. Apovian, professor of medicine at Harvard Medical School.

“The study explains why obesity is a disease: There are real changes in the brain. There were no signs of reversibility. The brains of obese subjects continued to lack the chemical reactions that tell the body, ‘Okay, you’ve had enough.'”

In her 2013 article “The Clinical and Economic Consequences of Obesity,” Apovian, also co-director of the Center for Weight Management and Wellness at Brigham and Women’s Hospital in Boston, points out that “obesity and its many serious comorbidities exert a heavy, both in human and economic terms.”

“More than one-third of US adults are obese and therefore subject to elevated rates of diabetes, hypertension, dyslipidemia and other risk factors for cardiovascular disease. The negative effect on the quality of life of these individuals is enormous.”

On the other hand, the coordinator Mireille Serlie warns of the need for caution when interpreting the findings of the study. “We don’t know when these profound changes occur in the course of weight gain. When the brain starts to slip and lose sensory capacity.”

“Eat less and exercise more” is not the answer

Obesity has a genetic component and, although the researchers try to account for it, excluding participants with childhood obesity, it is also possible that “genes are influencing the brain’s reaction to certain nutrients”, Farooqi points out.

In his view, much more research is needed to fully understand what obesity does to the brain, whether it is triggered by the fat tissue itself, the types of food eaten, or other environmental and genetic factors.

“Were there changes as people gained weight? Or were there things they ate when they were gaining weight, like ultra-processed foods, that caused a change in the brain? All of these alternatives are possible, and we really don’t know which one is right,” he says. the Cambridge professor.

While science addresses these questions, the study emphasizes that stigmatization has no place in the fight against obesity.

“The belief that you can solve being overweight simply by ‘eating less, exercising more’, and that not doing so is a lack of willpower, is so simplistic and so wrong,” says Serlie.

“I think it’s important for anyone struggling with obesity to know that a malfunctioning brain could be the reason why they struggle with food intake. And hopefully this information will increase empathy for their struggle.”