US researchers have found that the brain's response to food is linked to future weight gain in women and a gene that made the response to food weak, was responsible for weight gain later in life. In two separate studies, activity in the dorsal striatum of the brain was measured in one group of 43 women 18 to 22 and the second of 33 girls 14 to 18. They were given a chocolate milkshake or a tasteless drink and activity to the brain was measured as well as a genetic variant TaqA1 - which is linked to a fewer dopamine receptors in the brain. Dopamine is a chemical that controls and senses pleasure. Dr. Eric Stice, a senior scientist at the Oregon Research Institute who led the work said, "The more blunted your response to the milkshake taste, the more likely you are to gain weight."

Experts who have said that exercise and the right diet can keep excess weight at bay have also maintained that genetics has a major role to play as well, with dopamine being the biggest culprit. Dr. Stice said, "The evidence that this relation is even stronger for individuals at genetic risk for compromised signaling in these brain regions points to an important biological factor that appears to increase risk for obesity onset. It is possible that behavioural or pharmacological interventions that correct this reward deficit may help prevent and treat obesity."

Eating temporarily increases the dopamine levels and obese people have fewer dopamine receptors than the thinner people and the gene Taq1A1, is linked to fewer dopamine receptors. Dr. Nora Volkow of the National Institutes of Health, a dopamine specialist said, "This paper takes it one step farther. It takes the gene associated with greater vulnerability for obesity and asks the question why. What is it doing to the way the brain is functioning that would make a person more vulnerable to compulsively eat food and become obese?"

Dr David Haslam, a GP and clinical director of the National Obesity Forum said, "There is a debate about whether you can have a genuine addiction to food. But someone say on low dose heroin becomes resistant to the dopamine response and needs more and more. This is very interesting but it doesn't really help us now with tackling obesity," he said.

Stice said if the gene could be identified in children by doctors then they could be encouraged towards "recreational sports or other things that give them satisfaction and pleasure and dopamine that aren't food ... and not get their brains used to having crappy food."