Health UK (Commonwealth Union) – Cambridge researchers have uncovered distinctions in the hypothalamus, a pivotal brain region governing appetite, among individuals who are overweight or obese compared to those at a healthy weight. These revelations bolster the existing body of evidence highlighting the significance of brain structure in relation to weight and dietary habits.
Current estimations indicate that more than 1.9 billion people across the globe grapple with overweight or obesity. In the United Kingdom, as reported by the Office for Health Improvement & Disparities, nearly two-thirds of adults fall into these categories, elevating the risk of various health complications, such as type 2 diabetes, cardiovascular issues, stroke, cancer, and compromised mental well-being.
An array of factors shapes our eating behaviors, encompassing genetic predispositions, hormonal control, and environmental surroundings. The mechanisms within our brains that communicate hunger and satiety cues remain somewhat enigmatic, although studies have underscored the vital role played by the hypothalamus—a diminutive brain region akin to the size of an almond.
Dr. Stephanie Brown, affiliated with the Department of Psychiatry and Lucy Cavendish College at the University of Cambridge, emphasized the limited understanding of the hypothalamus in living humans due to its small size and difficulty in visualizing using conventional MRI scans, despite its known importance in appetite regulation.
While insights into the role of the hypothalamus primarily arise from animal studies, revealing intricate interconnected pathways that dictate feelings of hunger and fullness, Dr. Brown and her team adopted a unique approach. They harnessed a machine learning algorithm to scrutinize MRI brain scans from 1,351 young adults encompassing various BMI levels, aiming to discern variations in the hypothalamus across underweight, healthy weight, overweight, and obese individuals.
In a recent publication in Neuroimage: Clinical, the researchers divulged a significant enlargement of the hypothalamus in overweight and obese young adults, with a notable correlation between hypothalamic volume and body-mass index (BMI). Particularly conspicuous were these volume disparities within specific sub-regions governing appetite through hormone-releasing mechanisms that maintain hunger and fullness equilibrium.
Although the precise implications of this observation remain uncertain – whether the structural changes precede or result from alterations in body weight – one hypothesis relates to inflammation. Earlier animal studies have illustrated that a diet rich in fat can induce hypothalamic inflammation, leading to insulin resistance and obesity. In mice, as few as three days on a high-fat diet triggered such inflammation. Additionally, other research demonstrated that this inflammation heightened the threshold at which animals sensed fullness, implying an increased consumption of food to achieve satiety.
Dr Brown, the 1st author of the study, says “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 expansion of the hypothalamus in these individuals could potentially be attributed to inflammation, according to the researchers. A theory posits that the body’s response to inflammation might involve an enlargement of the brain’s specialized immune cells, referred to as glia.
Professor Paul Fletcher, the senior author of the study hailing from the Department of Psychiatry and Clare College at the University of Cambridge, indicated that the past twenty years have yielded significant revelations regarding appetite regulation and its potential modifications in obesity. Metabolic researchers at Cambridge have been at the forefront of these advancements.
“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.”
