Research: Feeling full
30 November 2007
Eating behaviour is influenced by hunger and the rewarding properties of food (which drive us to eat) and by satiety signals (which tell us we're full), but little is known about how the brain integrates information from these pathways.
Suspecting that the fat-derived hormone leptin might be involved, Sadaf Farooqi and Paul Fletcher, both Wellcome Trust Senior Fellows in Clinical Science from the University of Cambridge, studied two teenagers with congenital leptin deficiency. People with this condition eat excessively - even bland foods - but can be treated with leptin replacement therapy.
Functional magnetic resonance imaging was used to measure the subjects' brain activity as they were shown images of food, both before and after a week of leptin treatment.
Leptin altered brain activity in the ventral striatum, a brain area associated with pleasure and reward. The hormone also seemed to help the subjects to discriminate better between bland and tasty food. Before treatment, they strongly liked nearly all foods shown (from cauliflower to chocolate cake); after leptin replacement, the average scores fell.
Leptin was also important in linking the liking of food with hunger. Brain activation in a specific striatal region was triggered by images of well-liked food, whether the leptin-deficient subjects were fasting or full. In healthy controls - and in the treated subjects - the response was seen only when people were hungry.
The results suggest that leptin acts on the brain to decrease the perception of food reward and boost the response to satiety signals after eating.
References
Farooqi IS et al. Leptin regulates striatal regions and human eating behavior. Science 2007;317(5843):1355.