Obesity is a major threat to human health, often characterized by increased consumption of energy-dense and easy-to-eat, ‘effortless fast food’. In everyday life, we have to decide whether it is worth exerting effort to obtain rewards. The willingness to invest effort to obtain rewards (such as food) can also be measured in the lab. However, it is yet unclear whether obesity is associated with effort avoidance or rather with enhanced willingness to exert effort for (food) reward, with conflicting results in both rodent and human studies.
A factor that might explain these mixed findings is inflammation. Approximately half of individuals with obesity suffer from chronic increases in low-grade, systemic inflammation due to excess body fat. As you might recognize from being sick, inflammation during sickness also results in different behaviour, i.e. characterized by fatigue, anhedonia, depression, and apathy. Interestingly, lab studies that have acutely manipulated inflammation find that inflammation specifically affects effort expenditure, leaving reward processing unaffected. Animal studies found that these effects of inflammation on effortful behaviour depend on dopamine levels in the brain. Indeed, in human studies dopamine-rich brain regions are also most affected by inflammation manipulations.
Obesity-associated inflammation might explain low effort, high reward ‘fast food’ choices, via affecting brain dopamine levels; with excess of ‘fast food’ nutrients further worsening inflammatory tone, leading to a negative obesity spiral. However, the link between inflammation and effortful behaviour has never been studied in obesity. A better understanding of cost-benefit decision-making in obesity is of crucial importance to better explain why lifestyle changes to lose weight are so hard to maintain for the majority of individuals with an unhealthy weight.
Here, I will test the roles of inflammation and dopamine in effort-based decision making in obesity by employing task-based functional magnetic resonance imaging (fMRI), neurochemistry and measures of daily life decisions in combination with blood inflammatory markers. Using an anti-inflammatory intervention and dopamine manipulations, we will elucidate the crucial factors of the obesity spiral.
