Research published in the journal Science last week shows links between a common genetic variation, brain activity, BMI (body mass index) and long-term weight gain. Other recent studies have suggested that obese people may experience less pleasure when eating and eat more to compensate, but this is the first study to link that with future weight gain. The study, conducted by Eric Stice and colleagues at Oregon Research Institute in Eugene, US, asked 76 females aged between 14 and 22 to drink either a chocolate milkshake or a tasteless drink whilst having their brains scanned in a functional-MRI machine. Participants were also tested for a particular version of a gene called DRD2 - which is linked to fewer dopamine receptors in the brain - and were followed up a year later to see if they had gained weight.
The DRD2 gene variant is known to result in people getting less pleasure from food. The results of Dr Stice's study showed that women and girls with a high BMI, with and without the genetic variation, showed less activation in the dorsal striatum (an area of the brain associated with pleasure) when drinking the milkshake than women and girls with a lower BMI. Dr Stice and colleagues suggest that this may mean women and girls with higher BMI's are getting less pleasure from the food they eat and they may compensate by eating more.
When the team followed the participants up a year later they discovered that those with the gene variant had gained weight in inverse proportion to how active their striata were; that is, the less active their striata were, the more weight they had gained over the year. This result seems to fit with idea that getting less pleasure from the food you eat could cause you to eat more of it. However, participants without the DRD2 variant genes showed the opposite relationship between striata and weight; the more active their striatum had been the more weight they gained. This relationship suggests that the more pleasure people without the DRD2 mutation take from their food the more weight they gain over a year. Dr David Haslam, a GP and clinical director of the National Obesity Forum speaking to BBC News, said there were interesting parallels with the findings and addiction.