Size Of Hypothalamus May Explain Why Some People Become Obese

Over 1.9 billion people are estimated to be either obese or overweight on a global level, in America an estimated 114.8 million people are either overweight or obese, and in the UK almost two-thirds of adults are overweight or living with obesity. Regardless of where a person lives, being overweight or obese significantly increases the risks of developing a variety of health problems such as type 2 diabetes, heart disease, stroke, certain cancers, and even poorer mental health. 

There are a number of factors that influence how much we eat and what types of food we eat, such as genetics, hormone regulation, and the environment that we live in. But what happens within our brain to let us know that we are hungry is not fully understood, however, some research suggests that the hypothalamus plays an important role, although most of this work in animal studies. 

“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, University of Cambridge.

The researchers developed an algorithm using deep machine learning to analyze the brain scans from 1,351 young adults with a range of varied BMI scores to investigate differences in their hypothalamus regions, comparing those who are underweight, healthy weight, overweight, and those who are obese. 

The analysis revealed that the overall volume of the hypothalamus regions were significantly larger in those in the overweight and obese groups. In fact, according to the researchers, a significant relationship was found between the volume of the hypothalamus and body mass index, with the volume differences being most apparent in the sub-regions of the hypothalamus that control appetite through the release of hormones that balance hunger and fullness. 

Although the significance of their findings is unclear, possible reasons may be due to structural changes as a cause/consequence of the changes in body weight, or changes related to inflammation which in turn could prompt insulin resistance and obesity. Inflammation may explain why the hypothalamus is larger, as other research has shown that the body reacts to inflammation by making the glia larger. Regardless, more research is required to confirm what is causing the increase in volume, it may be a result of being overweight, or even a combination of factors. 

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.”

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.”