People with insulin resistance - a known precursor to type 2 diabetes - may have impaired responses to sugar intake in their brains that leads to a lower-than-normal release of the reward chemical dopamine, according to new data from the USA.
The study data, presented at the Society of Nuclear Medicine and Molecular Imaging's 2013 Annual Meeting, identifies an area of the brain that responds in a different way to sugar intake in people with insulin resistance - a finding that could 'revolutionise' understanding of how food-reward signalling contributes to obesity, say the authors.
"Insulin resistance is a significant contributor to obesity and diabetes," explained Professor Gene-Jack Wang of Stony Brook University - who led the research. "In this study we were able to confirm an abnormal dopamine response to glucose ingestion in the nucleus accumbens, where much of the brain's reward circuitry is located."
"This may be the link we have been looking for between insulin resistance and obesity," he added. "We suggest that insulin resistance and its association with less dopamine release in a central brain reward region might promote overeating to compensate for this deficit."
The research team used positron emission tomography (PET) imaging technology to monitor the brains of a total of 19 participants—including 10 healthy controls and nine insulin-resistant subjects— as they consumed drinks that were sweetened with sugar or the artificial sweetener sucralose.
"We gave a glucose drink to an insulin-sensitive control group and an insulin-resistant group of individuals and we compared the release of dopamine in the brain reward centre using PET," said Wang.
After each drink, the researchers mapped 'lit-up' areas of the brain and then gauged striatal dopamine receptor availability - which the team noted is inversely related to the amount of natural dopamine present in the brain.
The results were then matched with an evaluation in which patients were asked to document their eating behaviours, in order to assess any abnormal patterns in their day-to-day lives.
Results showed normal functioning of brain receptors, dopamine release and eating habits in both insulin-resistant and healthy controls when they were given sucralose.
However, when given glucose the insulin resistant participants were found to have "remarkably lower natural dopamine release" and had signs of disorderly eating behaviours when compared to the healthy controls.
The team suggested that the lowered chemical response to sugar may be indicative of a deficient reward system, which may potentially be setting the stage for insulin resistance and could increase the desire to consume more sugary food and beverages in order to overcompensate for the lack of reward.
"The findings set a path for future clinical studies using molecular imaging methods to assess the link of peripheral hormones with brain neurotransmitter systems and their association with eating behaviours," said Wang.