Region of the brain is different in people who are overweight or obese, University of Cambridge scientists show
Brain’s ‘appetite control centre’ different in people who are overweight or living with obesity
The brain’s appetite control centre - the hypothalamus - is different in people who are overweight or obese compared to those of a healthy weight, Cambridge scientists have shown.
The findings represent further evidence that brain structure is relevant to our weight and food consumption.
Almost two-thirds of adults in the UK are overweight or obese, according to the Office for Health Improvement & Disparities, and estimates suggest more than 1.9 billion people worldwide are above a healthy weight, increasing their risk of health problems including type 2 diabetes, heart disease and stroke, cancer and poorer mental health.
Factors including our genetics, hormone regulation and the environment in which we live are all known to be among the many factors influencing how much - and what - we eat.
The hypothalamus - a small region of our brain about the size of an almond - is also known to play a key role in our appetite, but what happens in our brains to tell us we are hungry or full is not fully understood.
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 have provided most of the evidence for the role of the hypothalamus in appetite regulation, showing complex interacting pathways within it and different cell populations acting together to tell us when we are hungry or full.
Dr Brown and colleagues sought to probe the hypothalamus in humans by using an algorithm developed using machine learning to analyse MRI brain scans taken from 1,351 young adults across a range of BMI scores.
It looked for differences in the hypothalamus when comparing individuals who are underweight, of healthy weight, overweight and living with obesity.
The overall volume of the hypothalamus was found to be significantly larger in the overweight and obese groups of young adults and there was a notable relationship between the volume of the hypothalamus and the body-mass index (BMI).
Reporting their findings in a study published on Tuesday (August 7) in Neuroimage: Clinical, the team found the volume differences were most apparent in sub-regions of the hypothalamus that control appetite through the release of hormones to balance hunger and fullness.
Whether the structural changes are a cause or a consequence of the changes in body weight is not yet clear.
But one possibility is that inflammation lies at the heart of the change.
Previous animal studies have shown that a high fat diet can cause inflammation of the hypothalamus, prompting insulin resistance and obesity.
Just three days of a fat-rich diet in mice is known to cause this inflammation.
Other studies have shown such inflammation can raise the threshold at which animals feel they are full, prompting them to eat more than usual.
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.”
The body may be reacting to inflammation by increasing the size of the brain’s specialist immune cells, known as glia.
Prof 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 will be needed to confirm whether the increased volume in the hypothalamus is a result of being overweight or whether people with larger hypothalami are predisposed to eat more.
These two factors may also be interacting, causing a feedback loop.
The research was supported by the Bernard Wolfe Health Neuroscience Fund, Wellcome and the NIHR Cambridge Biomedical Research Centre, with additional funding from Alzheimer’s Research UK.
