Overweight People’s Brain Appetite Control Differs

Cambridge researchers discovered that the hypothalamus, a critical part of the brain involved in hunger control, differs in the brains of people who are overweight or obese compared to persons who are a healthy weight.

According to the researchers, their findings add to the evidence that brain anatomy influences weight and food consumption.

According to current estimates, nearly 1.9 billion individuals worldwide are either overweight or obese. According to the Office for Health Improvement and Disparities, about two-thirds of adults in the United Kingdom are overweight or obese. This increases a person’s chance of acquiring a variety of health issues, including as type 2 diabetes, heart disease and stroke, cancer, and poor mental health.

A variety of factors, including our genetics, hormone regulation, and the environment in which we live, determine how much and what we eat. It’s unclear what happens in our brains to notify us when we’re hungry or full, but studies have indicated that the hypothalamus, a small part of the brain about the size of an almond, plays a crucial role.

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

Animal studies provide the majority of evidence supporting the hypothalamus’s function in appetite regulation. These findings indicate that the hypothalamus contains complex interaction pathways in which different cell populations collaborate to tell us when we are hungry or full.

To get around this, Dr. Brown and colleagues used a machine learning algorithm to analyze MRI brain scans from 1,351 young adults with varying BMI scores, looking for differences in the hypothalamus when comparing individuals who are underweight, healthy weight, overweight, and obese.

The team discovered that the overall volume of the hypothalamus was considerably greater in the overweight and obese groups of young people in a study published today in Neuroimage: Clinical. In fact, the researchers discovered a link between hypothalamic volume and body mass index (BMI).

These volume changes were especially noticeable in hypothalamic subregions that govern appetite by releasing hormones to balance hunger and fullness.

While the specific relevance of the discovery is unknown, including whether the structural alterations are a cause or a result of changes in body weight, one theory is that the change is related to inflammation. Previous animal research have demonstrated that a high fat diet can produce hypothalamic inflammation, which leads to insulin resistance and obesity. In mice, three days of a high-fat diet is adequate to trigger inflammation. Other research have shown that this inflammation might raise the threshold at which animals are full, requiring them to consume more food than usual to be satisfied.

Dr Brown, the study’s first author, added: “If what we see in mice is the case in people, then eating a high-fat diet could trigger inflammation of our appetite control centre. Over time, this would change our ability to tell when we’ve eaten enough and to how our body processes blood sugar, leading us to put on weight.”

According to the researchers, inflammation may explain why the hypothalamus is larger in these people. One theory is that the body responds to inflammation by expanding the size of the brain’s specialised immune cells, known as glia.

Professor Paul Fletcher, the study’s senior author, from the Department of Psychiatry and Clare College, Cambridge, said: “The last two decades have given us important insights about appetite control and how it may be altered in obesity. Metabolic researchers at Cambridge have played a leading role in this.

“Our hope is that by taking this new approach to analysing brain scans in large datasets, we can further extend this work into humans, ultimately relating these subtle structural brain findings to changes in appetite and eating and generating a more comprehensive understanding of obesity.”

More research is needed, according to the researchers, to determine whether increased volume in the hypothalamus is a result of being overweight or whether persons with larger hypothalami are prone to eat more in the first place. It is also feasible that these two factors will interact, resulting in a feedback loop.

The Bernard Wolfe Health Neuroscience Fund, Wellcome, and the NIHR Cambridge Biomedical Research Centre provided funding for the study, which was supplemented by Alzheimer’s Research UK.

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