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According to a new study, obesity would cause irreversible changes in our ability to feel satiety.

A study, published on June 12 in the scientific journal Nature Metabolism, reveals that obesity would modify the brain and prevent an overweight person from feeling the effect of satiety. These changes would probably be irreversible, since even after losing weight, the brain of an obese person does not recover the ability to understand when the body is no longer hungry. 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 said: “There was no sign of reversibility – the brains of obese people continued to lack the chemical responses that tell the body, ‘OK, you’ve eaten enough‘”. This finding would explain, at least in part, why many people often regain the pounds they lost.

The effects of obesity on our health

This study is 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. Dr Mireille Serlie, professor of endocrinology at Yale School of Medicine in New Haven, Connecticut and lead author of the study said: “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.“.

The day before the test, the participants ate the same meal and did not swallow anything else until the time of the test. The researchers then used functional magnetic resonance imaging and single-photon emission tomography to capture the brain’s reaction over a 30-minute period. In people at a healthy weight, the striatum, the part of the brain involved in food motivation, slowed when sugars or fats were digested, demonstrating that the brain was recognizing that the body had been fed. Additionally, the dopamine level rose to a normal amount, a sign that the brain felt rewarded. However, in obese people, the results were different: brain activity did not slow down and dopamine levels did not increase. This observation was particularly true during the ingestion of fats and lipids. In the three months following the first test, the obese subjects had to lose 10% of their weight, to repeat the tests. The results of the second test showed no changes, even after losing weight, the subjects did not recover their ability to feel satiety.

How do you know if you are overweight?

According to the medical definition, obese people have a body mass index, or BMI, greater than 30, while the weight considered “normal”, corresponds to a BMI between 18 and 25. The BMI is calculated from height and weight according to the following formula: BMI = weight in kg/height² (in m) .

The latest projections from the World Health Organization (WHO) indicate that at least one in three adults worldwide is overweight and nearly one in 10 adults is obese. There are also more than 40 million children under the age of five who are overweight.

In France, overweight concerns 45% of people, including 14% suffering from obesity. The prevalence of obesity is higher in the northern part of France where it exceeds 20% in certain departments, as well as in the DROMs, except Reunion.


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