A recently published study in the Molecular Psychiatry journal entitled “Weight loss after bariatric surgery normalizes brain opioid receptors in morbid obesity” finds that patients with obesity have lower levels of brain acting substance called μ-opioid receptor. Lower levels of these receptors have an impact on behaviors that lead to obesity, which may be positively impacted through weight loss methods such as bariatric surgery.

Obesity is a disorder identified by excessive body fat. Worldwide, about 10% of the population is considered obese and severe cases are recorded in countries such as the United States, Australia, and Canada. The condition is caused by various factors including genetic predisposition, diet, lifestyle, infections and other medical problems like eating disorders. Patients with obesity may suffer from back or joint pain, skin rashes, weight gain, sleep disorder, depression, and fatigue among others. They may also have reduced life expectancy and possible medical complications such as with type 2 diabetes, heart problems, and certain types of cancer. Obesity can be managed by increased physical exercise, changes in diet, anti-obesity medications, and bariatric surgery where the stomach is surgically divided or reduced in size. Among the proposed therapies, bariatric surgery is considered the most effective method for several reasons such as:  i) improvement in obesity conditions, ii) long-term weight loss of about 14% to 25% for a period of 10 years, and iii) decreased overall mortality by 29%.

There are many possible pathophysiological mechanisms involved in development of obesity including genetic mutations and hormones that affect the appetite. Previously performed studies using a medical functional imaging technique named positron emission tomography (PET) suggested that patients with obesity suffer from dysfunction in substances that act on the nervous system and are effective as pain relievers such as for managing pain following surgery. However, little is known about opioid dysfunction and its association with obesity. To clarify, the researchers examined the role of opioid system in obese patients undergoing weight loss by means of bariatric surgery.

In this study, a total of 16 female patients with obesity and 14 control subjects participated. The experiment consisted of measuring substances found in the brain called μ-opioid receptor (MOR) and dopamine D₂ receptor (D₂R) by means of PET scanning. The scan was performed before and 6 months after bariatric surgery, with results suggesting that levels of brain MOR in the obese patients was initially low, but increased by 23% after the weight loss surgery was performed. Furthermore, brain scans depicted changes that occurred in brain regions related to areas involving reward processing. On the other hand, no change in dopamine levels, supposedly known for its involvement in the rewarding process, was observed in any of the brain regions after weight loss surgery.

In summary, these findings highlight the important role of the opioid system in obesity syndrome. The data demonstrated that low levels of MOR could be associated with obesity. However, further investigations are required to gain in-depth understanding of the mechanisms of MOR associated obesity that may lead to development of future therapeutic targets.