The study, published in the Journal of Clinical Endocrinology & Metabolism (JCEM), investigated whether the signalling pathways associated with a gene mutation linked to obesity – known as the melanocortin-4 receptor (MC4R) – plays a role in the rood rewards system by studying the brain activation response to food cues in people with and without MC4R mutations.
Led by Agatha van der Klaauw of the Wellcome Trust-MRC Institute of Metabolic Science at Addenbrooke's Hospital in Cambridge, U.K, the team behind the study noted that the MC4R mutation occurs in around 1% of obese people and is thought to contribute to weight gain from an early age.
"In our study, we found that people with the MC4R mutation responded in the same way as normal weight people, while the overweight people without the gene problem had a lower response," said van der Klaauw.
"In fact, the brain's reward centres light up when people with the mutation and normal weight people viewed pictures of appetizing foods. But overweight people without the mutation did not have the same level of response."
Such a finding is intriguing as it shows a completely different response in two groups of people of the same age and weight, said the team.
"For the first time, we are seeing that the MC4R pathway is involved in the brain's response to food cues and its underactivity in some overweight people," van der Klaauw said. "Understanding this pathway may help in developing interventions to limit the overconsumption of highly palatable foods that can lead to weight gain."
The team compared three groups of people: eight people who were obese due to a problem in the MC4R gene, 10 people who were overweight or obese without the gene mutation and eight people who were normal weight. They performed functional Magnetic Resonance Imaging (fMRI) scans to look at how the reward centres in the brain were activated by pictures of appetising foods like chocolate cake compared to bland food like rice or broccoli and non-food items such as staplers.
The scans revealed that obese people with the MC4R mutation had similar activity in the reward centres of the brain when shown a picture of a dessert like cake or chocolate as normal weight people. However, they reported that these reward centres were underactive in overweight and obese people who did not have the gene mutation.
“These findings are consistent with a role for central melanocortinergic circuits in the neural response to visual food cues,” the ream concluded.
Published online ahead of print, doi: 10.1210/jc.2014-1651
“Obesity-Associated Melanocortin-4 Receptor Mutations Are Associated With Changes in the Brain Response to Food Cues”
Authors: Agatha A. van der Klaauw, Elisabeth A. H. von dem Hagen, et al