In Friday's issue of the journal Science, psychology researchers in Texas, Oregon and Connecticut reported that they were able to predict future weight gain in young women, by analyzing their reactions to milkshakes.

Brain scans on 43 female college students ages 18 to 22 and 33 teenagers, ages 14 to 18, while they drank either a chocolate milk shake or a tasteless solution were made. Cells in the brain's "reward" centers release dopamine when people eat, causing that feeling of pleasure, researchers explain.

The brains study revealed that obese people actually enjoy food less and in order to make up for the missing enjoyment, obese people eat more high-calorie food. "We originally thought obese people would experience more reward from food. But we see obese people only anticipate more reward; they get less reward. It is an ironic process," Stice tells WebMD.

The functional magnetic resonance imaging scans showed that activity in the brain's dorsal striatum area was much weaker in weighty women. After a year, however, participants who displayed the blunt response were more likely to have put on weight.

It is known that eating can temporarily boost dopamine levels. Previous brain scans have suggested that the obese have fewer dopamine receptors in their brains than lean people. And a particular gene version, called Taq1A1, is linked to fewer dopamine receptors.

Although past research has shown that biological factors play a major part in obesity, the study is one of the first to positively identify factors that increase people's weight gain risk in the future.