Central opioid receptors that regulate reward and emotion in the brains of men with chronic obesity react to hunger and feeding differently than receptors in the brains of lean men, according to research in The Journal of Clinical Endocrinology & Metabolism.
In a preliminary study of both lean men and men with obesity from the Investigational Weight Management Clinic at The University of Michigan, researchers found that men with obesity showed reduced central mu-opioid receptor (MOR) activity when compared with lean men, and that MOR activity was partially recovered following a period of 15% weight loss.
“The systems in the brain that help regulate emotion and reward are quite responsive to eating,” Paul R. Burghardt, PhD, of the department of psychiatry at The University of Michigan in Ann Arbor and the department of nutrition and food science at Wayne State University in Detroit, told Endocrine Today. “However, a state of chronic obesity appears to dampen the activity of the central opioid system.”
Paul R. Burghardt
Burghardt and colleagues analyzed data from seven lean healthy men (mean age, 52 years) and seven men with chronic obesity (mean age, 51 years) matched for age and ethnicity in a university medical center setting. Researchers used PET scans to measure mu-opioid receptor availability. Researchers scanned the lean and healthy men under fasted and fed conditions; researchers performed PET scans on the men with obesity at baseline and following a very low-calorie diet (800 kcal per day) to achieve 15% weight loss.
Researchers found trends for greater MOR non-displaceable binding potential following an overnight fast in lean men compared with men with obesity in areas of the brain regulating affect and emotion. In the areas that regulate homeostatic control of energy (thalamus), researchers found a greater non-displaceable binding potential in the lean men compared with men with obesity before weight loss.
Receptor non-displaceable binding potential increased in men with obesity after weight loss compared with their baseline measurements in the left temporal pole, ventral striatum, thalamus and medial frontal cortex, however, MOR activity had not completely recovered, according to researchers.
“These studies give us some initial insight into the mechanisms through which eating impacts emotion and how much we like what we eat,” Burghardt said. “Since there is a very high recidivism following weight loss, this has potential for providing additional tools that regulate central opioid systems, emotion, and reward for clinical weight management.”
“Since this was a pilot study in men, we need to include women moving forward,” Burghardt said. “We also really need to understand if the differences between lean and obese individuals are an inherent, or a response to chronic energy imbalance.”– by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.