The brain of obese people does not ‘control’ appetite in the same way

The amount of food we eat each day, as well as the type of food we choose, are influenced by a large number of factors, including everything from our genetics and hormonal regulation, to the environment around us or the emotions we experience. It is not known exactly what happens in our brain to activate the feeling of hunger or satietybut it seems that a small brain region known as the hypothalamus plays a key role in appetite control.

Knowing how it works could help us better understand why some people are more prone to gaining weight than others, and now new research by scientists at the University of Cambridge has shown that the hypothalamus is different in the brains of overweight and obese people compared to people who have a healthy weight. According to the researchers, these findings highlight the importance of brain structure in weight and food consumption.

The World Health Organization (WHO) estimates that there are more than 1.9 billion people who are overweight or obese, a public health problem that increases the risk of developing cardiovascular diseases, type 2 diabetes, cancer or mental disorders, and also affects to the smallest, since this same body estimated the number of children under five years of age with excess weight in 2019 at 38.2 million.

“A high-fat diet could trigger inflammation in our appetite control center and change our ability to distinguish when we’ve eaten enough.”

Dr Stephanie Brown, from the Department of Psychiatry and Lucy Cavendish College, University of Cambridge, said: “Although we know the hypothalamus is important in determining how much we eat, we actually have very little direct information about this region of the brain in humans. alive. That’s because it’s so small and hard to make out on traditional brain MRIs.”

Therefore, most of the evidence that has been found on the role of the hypothalamus in appetite regulation comes from animal studies, which have shown that there are complex interaction pathways within the hypothalamus, with different populations of cells acting together to tell us when we are hungry or full.

A larger hypothalamus in people who are obese or overweight

The researchers used an algorithm developed with machine learning to analyze brain MRIs of 1,351 young adults on a range of body mass index (BMI) scores to look for differences in the hypothalamus when comparing underweight, healthy weight, overweight, and obese individuals.

They found that the overall volume of the hypothalamus was significantly greater in the overweight and obese groups of young adults. In fact, Dr. Brown and her team found a significant relationship between hypothalamus volume and BMI, and these volume differences were most apparent in those subregions of the hypothalamus that control appetite through the release of appetite-balancing hormones. hunger and satiety.

These findings have been published in the journal Neuroimage: ClinicalAlthough the researchers do not know if the structural changes they have detected are a cause or a consequence of the changes in body weight, although they could be related to inflammation, since previous studies in animals have shown that a high-fat diet can cause the inflammation of the hypothalamus, which in turn leads to insulin resistance and obesity.

For example, in tests on mice it has been observed that after only three days of feeding on a high fat diet This inflammation already occurs. Other studies have shown that this inflammation can raise the threshold at which animals are satiated, meaning they have to eat more food than normal to feel full.

“If what we see in mice occurs in people as well, then eating a high-fat diet could trigger inflammation in our appetite control center. Over time, this would change our ability to distinguish when we have eaten enough and how our body processes blood sugarwhich leads us to gain weight”, explained Dr. Brown.

Inflammation may explain why the hypothalamus is larger in these individuals, the researchers note, noting that more research is needed to confirm whether the increased volume in the hypothalamus is the result of being overweight, or if people with a larger hypothalamus large are predisposed to eat more. It is also possible that both factors interact with each other, triggering a feedback loop.

“Our hope is that by taking this new approach to analyzing brain scans in large data sets, we can further extend this work to humans and ultimately link these subtle structural brain findings to changes in appetite and feeding and generating more comprehensive understanding of obesity”concludes Professor Paul Fletcher, from the Department of Psychiatry and Clare College, Cambridge and lead author of the study.


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