The impact of insulin on dopamine levels could play an important role in eating behaviour, a new study has indicated.

A team from the German Center for Diabetes Research looked at the impact of insulin on the specific part of the brain which regulates reward processes, reporting that this relationship could be behind the brain’s regulation of glucose metabolism and people’s eating habits.

First author Stephanie Kullmann explained: “Our eating behaviour is regulated by the interaction between the reward system and homeostatic systems. Studies indicate that insulin also acts in dopamine-driven reward centres in the brain. It has also been shown that obesity leads to changes in the signalling of the brain that have a negative effect on the glucose metabolism in the whole body.

“We now wanted to decipher the interaction between the two systems in humans and find out how insulin regulates the dopamine system.”

The study saw 10 healthy, normal weight male participants receive either insulin or a placebo through a nasal spray, meaning it reaches the brain directly.

Magnetic imaging helped the researchers to assess dopamine levels in the brain, showing that the insulin reduced dopamine levels and crucially, led to changes in the brain’s network.

Professor Martin Heni said: “The study provides direct evidence of how and where in the brain signals triggered after eating – such as insulin release and the reward system interact.

“We were able to show that insulin is able to decrease dopamine levels in the striatum in normal-weight individuals. The insulin-dependent change in dopamine levels was also associated with functional connectivity changes in whole-brain networks. Changes in this system may be an important driver of obesity and related diseases.”

Now researchers want to conduct similar studies in participants who are diabetic or obese, as they often experience insulin resistance in the brain.

Longer term, the aim is to explore how normal insulin activity in the brain can be restored through behavioural change and/or pharmaceutical involvement.

The study has been published in the Journal of Clinical Endocrinology & Metabolism.

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