New research from the US suggests that certain people may have a genetic predisposition to obesity because the reward centres in their brains respond sluggishly after eating, so to get more pleasure from eating they opt for foods denser in calories which makes them gain weight.
The study was done by Eric Stice, psychology researcher at The University of Texas at Austin, and colleagues from other establishments in the US, and is published in the 17 October issue of Science.
Stice has been studying eating disorders and obesity for nearly 20 years. He said that this study:
“Reveals obese people may have fewer dopamine receptors, so they overeat to compensate for this reward deficit.”
When a person eats, their brain’s reward centre responds by releasing the messenger molecule dopamine. But Stice and colleagues found that compared to the brains of lean people, the brains of obese people showed less activation in the striatum, the part of the brain that expresses dopamine receptors.
The researchers also found that individuals whose striata were less active during eating were the ones most likely to become overweight, particularly if they had a gene called TaqIA that is linked to having fewer dopamine receptors.
Stice said that people with fewer dopamine receptors:
“Need to take in more of a rewarding substance — such as food or drugs — to experience the same level of pleasure as other people.”
For the study, Stice and colleagues used Functional Magnetic Resonance Imaging (fMRI) to watch activity in the dorsal striatum of female participants while they consumed a chocolate milkshake and then while they consumed a tasteless solution. They did this twice, once with 43 female students aged 18 to 22 and then also with 33 teenage girls aged 14 to 18.
They also tested both groups to find out which individuals had the Taq1A1 gene, which meant they had a lower number of dopamine D2 receptors.
Stice and colleagues then followed the participants for 12 months and monitored changes in their body mass index (BMI).
The results showed that participants whose striata were less active when they drank the milkshake and who also had the Taq1A1 gene were the ones most likely to put on weight over the follow up period.
Stice said understanding how the dopamine receptor deficit affects the brain’s reward circuits and their response to eating is important for the development of treatment options that could target this effect in people at higher risk of unhealthy weight gain.
There is an interesting parallel between these findings and drug addiction. For example, heroin addiction can start with low doses of heroin, which blunts the dopamine response and this leads the person to take stronger and stronger doses to get the same feeling of reward.
The clinical director of the National Obesity Forum in the UK, Dr David Haslam, who is also a GP told the BBC there is a debate about whether you can have a similar addiction to food.
“Relation Between Obesity and Blunted Striatal Response to Food Is Moderated by TaqIA A1 Allele.”
E. Stice, S. Spoor, C. Bohon, and D. M. Small
Science 17 October 2008: Vol. 322. no. 5900, pp. 449 – 452.
DOI: 10.1126/science.1161550
Source: University of Texas at Austin.
Written by: Catharine Paddock, PhD.