Scientists have identified the brain circuits that 'decide' how much we eat. Using live brain scanning techniques and an innovative study design, researchers have discovered how the brain controls food intake in humans. Their findings are published in Nature.
The group of scientists from UCL (University College London) and King's College London used peptide YY (PYY), a naturally occurring hormone that regulates appetite, to investigate which areas of the brain are involved in controlling food intake. Studies in animals had suggested that PYY acted on the homeostatic regions of the brain (hypothalamus and brainstem), which govern primitive functions. However, there was no information on how this hormone regulates eating in humans.
This latest research, led by Medical Research Council clinician scientist Dr Rachel Batterham, used functional Magnetic Resonance Imaging (fMRI). It showed that PYY not only targets the primitive homeostatic parts of our brain that control feeding but also acts in the cortico-limbic brain regions that determine the rewarding and pleasurable aspects of eating.
Dr Batterham, based at UCL, said: "We were surprised to discover that the greatest change in brain activity in response to PYY was within the orbito frontal cortex (OFC), a region thought to act as an integrative hub and implicated in reward processing. More surprisingly we found that the change in OFC activity predicted how much food the volunteers subsequently ate. The greater the change in activity in that area, the less the subjects ate."
Eight normal weight men took part in a double blind placebo-controlled study. After 14 hours without food subjects were given an intravenous drip of either PYY or placebo for 100 minutes while their brain was scanned continuously. Thirty minutes later they were offered an unlimited meal. Each subject was tested twice one week apart, once with PYY and once with the placebo in a random order. PYY infusion reduced food consumption in all 8 subjects and on average caused a 25% reduction in the calories eaten.