Brain structure could make some people want to eat more than others, study finds

How the brain controls hunger and appetite may be different for people who are obese, a new study has suggested.

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

Current estimates suggest that more than 1.9 billion people worldwide are either overweight or obese.

According to the Office for Health Improvement and Disparities, almost two-thirds of adults in the UK are overweight or living with obesity.

This increases the risk of developing health issues like type 2 diabetes, heart disease and stroke, cancer and poorer mental health.

The new study from the University of Cambridge focused on what happens when our brain tells us we are either hungry or full.

Past studies have shown that the hypothalamus – a small region of the brain about the size of an almond – plays an important role, but it is little understood.

The majority of evidence for the role of the hypothalamus in appetite regulation comes from animal studies, which indicate complex interacting pathways within the hypothalamus, with different cell populations acting together to tell us when we are hungry or full.

To get around this researchers used an algorithm developed using machine learning to analyse brain scans taken from 1,351 young adults across a range of BMI scores.

They looked for differences in the hypothalamus when comparing individuals who are underweight, healthy weight, overweight, or living with obesity.

According to the findings, the overall volume of the hypothalamus was significantly larger in the overweight and obese groups of young adults.

The researchers describe a significant relationship between volume of the hypothalamus and body mass index (BMI).

The 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 exact significance of the finding is unclear, one explanation is that the change relates to inflammation, the researchers suggest.

Previous animal studies have shown that a high-fat diet can cause inflammation of the hypothalamus, which in turn prompts insulin resistance and obesity.

In mice, just three days of a fat-rich diet is enough to cause this inflammation.

Other studies have shown that this inflammation can raise the threshold at which animals are full – in other words, they have to eat more food than usual to feel full.

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

More research is needed to confirm whether increased volume in the hypothalamus is a result of being overweight or whether people with larger hypothalami are predisposed to eat more in the first place.

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