Brain’s appetite control centre different in overweight, obese people

LONDON: Scientists have found that the hypothalamus, a key region of the brain involved in controlling appetite, is different in the brains of people who are overweight and people with obesity when compared to people who are a healthy weight.

The findings add further evidence to the relevance of brain structure to weight and food consumption.

Current estimates suggest that over 1.9 billion people worldwide are either overweight or obese. This increases an individual’s risk of developing a number of health problems, including Type 2 diabetes, heart disease and stroke, cancer and poorer mental health.

What happens in our brains to tell us that we are hungry or full is not entirely clear, though studies have shown that the hypothalamus, a small region of the brain about the size of an almond, plays an important role.

"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," said Dr Stephanie Brown from the Department of Psychiatry and Lucy Cavendish College at University of Cambridge.

In the study, published in the journal Neuroimage: Clinical, the team used an algorithm developed using machine learning to analyse MRI brain scans taken from 1,351 young adults across a range of BMI scores, looking for differences in the hypothalamus when comparing individuals who are underweight, healthy weight, overweight and living with obesity.

They found that the overall volume of the hypothalamus was significantly larger in the overweight and obese groups of young adults. In fact, the team found a significant relationship between volume of the hypothalamus and body-mass index (BMI). These volume differences were most apparent in those sub-regions of the hypothalamus that control appetite through the release of hormones to balance hunger and fullness.

While the precise significance of the finding is unclear -- including whether the structural changes are a cause or a consequence of the changes in body weight -- one possibility is that the change relates to inflammation.

"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," said Dr Brown.

Inflammation may explain why the hypothalamus is larger in these individuals, the team said. One suggestion is that the body reacts to inflammation by increasing the size of the brain’s specialist immune cells, known as glia.