11/11/08 A new study in the November issue of the journal Appetite finds that obese women display significantly weaker impulse control than normal-weight women, but between obese and normal-weight men, the impulsivity levels are nearly the same. The study was conducted by researchers in the University of Alabama at Birmingham (UAB) Department of Psychology.

UAB researchers conducted the study to see how obese and normal-weight men and women differed in their decision-making skills, specifically in delay discounting, the measure of how much an individual is driven by immediate gratification versus the willingness to wait for delayed but greater rewards.

In the study of 95 men and women, UAB researchers gave the participants the choice of receiving varying hypothetical amounts of money immediately or fixed hypothetical amounts of money to be received after delays of two weeks, one month, six months or one, three, five or 10 years. The hypothetical rewards ranged from $1,000 to $50,000. The researchers found that obese women discounted the value of future rewards at a rate three-to-four times greater than that of normal-weight women, suggesting greater impulsivity. Obese men, however, and the male and female control subjects all showed similar levels of delay discounting. The results were the same even when the researchers controlled for differences in IQ and income, both of which have been found to be related to measures of impulsivity.

One explanation for the differences between men and women may be found in a personality trait known as eating-related disinhibition, which is the tendency to overeat in response to certain situations or cues such as a big display of dessert, said UAB researcher Rosalyn Weller, Ph.D., the study's principle investigator. Previous studies have shown that those who score higher in disinhibition have higher body mass indexes and gain weight more easily, she said. However, men score lower in disinhibition than women.

"Our study found that obese men have more impulse control than obese women. So, obese men may be protected from more impulsive behavior on the delay-discounting task by having lower disinhibition in general. Obese women may have the double whammy of being female and having higher body mass index," Weller said.

The UAB researchers are now conducting delay-discounting studies using functional brain imaging (fMRI). The researchers are using the UAB Civitan International Research Center's 3 Tesla head-only magnet to investigate what happens in the brains of obese individuals who vary in impulsivity as they make decisions.