They found that obese people had less activity in the part of the brain that controls release of dopamine (which is a chemical that gives you a pleasure ‘high’) than people of a healthy body weight. As they do not get satisfied when they eat it is likely they overeat to the point of becoming obese.
Written by Dr. Noel Duncan
Stice, E, Spoor, S, Bohon, C & Small, DM. Relation between obesity and blunted striatal response to food is moderated by TaqIA A1 allele. Science. 2008 Oct 17; 322(5900):449-52.