Researchers at the University Hospital of Amsterdam and Yale University have discovered that the brains of obese people react differently to eating food compared to healthy people. This finding, published in the journal Nature Metabolism, provides an explanation for why it is more difficult to lose weight than to regain it.
According to the results, the release of dopamine in the brain after eating is lower in obese individuals compared to non-overweight individuals. This phenomenon is observed in the striatum, a brain region responsible for regulating motivation for food. Since dopamine is related to feelings of gratification, this finding suggests that obese people get less gratification from the same amount of food, which could lead them to overeat.
In addition to the striatum, obesity has been shown to affect the reaction of multiple brain regions, including the frontal, temporal, parietal, and occipital cortex, as well as deeper regions of the brain. In all these areas, a less intense response has been observed in people with obesity compared to those who are not overweight.
A relevant fact is that losing 10% of body weight in a period of twelve weeks is not enough for the brain of a previously obese person to return to the state of a person with ideal weight. Even though they have lost weight, their striatum still releases little dopamine after eating, and other brain regions still show a weak response. This could explain why most people regain weight after initially losing it.
Previous research in mice had shown that signals from the digestive system regulate behaviors related to food intake in the brain. However, studies in humans were lacking to confirm whether the same phenomena occurred in the human body.
The study involved 30 people with obesity and 30 people with ideal weight, both men and women, with an average age of 60 years. The participants agreed to be fed through a nasogastric tube, while their brain reactions were assessed using neuroimaging techniques.
The results revealed the existence of a communication pathway between the digestive system and the brain that induces people with obesity to overeat, regardless of the sensory pleasure of the food, since the participants could not taste, chew or eat it.
It should be noted that the experiments were carried out with infusions of carbohydrates and lipids, but not proteins, which activate more complex communication channels between the digestive system and the brain in studies with mice.
This study provides a fundamental advance in understanding the communication mechanisms that regulate food intake in people with obesity, according to Mary Elizabeth Baugh and Alexandra DiFeliceantonio, of the Fralin Biomedical Research Institute in Virginia, in a review article published in Nature Metabolism. They also point out that due to frequent weight regain after loss, this study lays the foundation for future research exploring how signaling between the gut and the brain may influence weight loss maintenance or recovery.
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