Elevated Reward Response Linked to Weight Gain, Substance Use

Nancy A. Melville

June 05, 2012

June 5, 2012 (Phoenix, Arizona) – Heightened responsivity to food and monetary rewards in key regions of the brain is associated not only with weight gain but also with an increased risk for substance use, new research suggests.

A prospective brain imaging study using functional magnetic resonance imaging (fMRI) showed that adolescents with elevated responsivity to rewarding stimuli were at increased risk for unhealthy weight gain and initiation and escalation of substance use.

The study is the first to demonstrate a link between oversensitization to rewards, rather than a blunted response, or hyporesponsivity, with substance use, said lead investigator Eric Stice, PhD, of the Oregon Research Institute in Eugene.

"To my knowledge, this is the first prospective fMRI test of this reward surfeit vs reward deficit model," Dr. Stice said.

The findings were presented here at the New Clinical Drug Evaluation Unit (NCDEU) 52nd Annual Meeting.

The researchers initially set out to assess the relationship between hypersensitivity and reward only in terms of food and weight gain but quickly realized that they could include substance abuse in the model.

"Considering the vulnerability factors for overeating are similar to those for drug and alcohol abuse, we decided to also test substance abuse," said Dr. Stice.

Erosion of Reward

The researchers prospectively evaluated fMRI images of 162 male and female adolescents during the course of 1 year. The mean age of the participants was 15.3 years.

At 1-year follow-up, investigators found that adolescents with an elevated response to rewarding stimuli in the caudate, putamen, middle cingulate gyrus, and midbrain to rewarding stimuli were at an increased risk for weight gain and initial onset and future escalation of substance use.

"It really provides evidence that it is this hypersensitive reward surfeit, this hyper-responsive reward circuitry, that gets us as much in trouble with drugs and alcohol as it does with overeating," he said.

Previous research has suggested that the reward deficit model may be associated with elevated response once a person has already gained weight or become dependent on a substance.

In 2010, Dr. Stice and colleagues conducted a study of 26 women who completed a taste test in which their striatal responses were measured upon tasting a chocolate milkshake and were then compared with responses upon tasting a tasteless solution. At a 6-month follow-up, the investigators found that women who had gained weight showed reduced striatal response to the milkshake, compared with their baseline measurements and with the response of control participants who had not gained weight.

"We found that overeating, particularly energy-dense food, reduces striatal response to food," Dr. Stice said. "This suggests that overeating leads to an erosion of reward from food intake, which may increase risk for escalated intake."

Interestingly, although the new study found the same triggers behind weight gain and substance abuse, there was no correlation between those who gained weight and those who fell into substance abuse (r = .08).

"This suggests that those who have excess weight gain and onset of drug and alcohol abuse are different people," Dr. Stice said. "It really plays into this notion that there is a great deal of specificity in how we develop relationships with certain behaviors."

The findings have important implications in terms of appropriate interventions for overeating, he noted.

"All of these data suggest that gradual, healthy changes to dietary intake instead of dramatic ones such as weight loss diets may be better at minimizing activation of opponent processes that produce frugal metabolism," Dr. Stice said.

Sheds New Light

According to Mark S. Gold, MD, the findings shed important new light on the complex mechanisms that explain why some people are more prone to addictive behaviors such as overeating and substance abuse.

"Learning why and how some people can consistently say no is a bridge to augmenting that neurocognitive and brain systems that are easily influenced," said Dr. Gold, who is chair of the Department of Psychiatry, distinguished professor, and Donald R. Dizney Eminent Scholar at the University of Florida in Gainesville.

"[Dr. Stice] is working to develop a mechanism, active in all of us, before our systems break down from the weight of overeating," he added.

"His work is novel and extremely reproducible."

The study was funded by the National Institutes of Health. Dr. Stice and Dr. Gold have disclosed no relevant financial relationships.

New Clinical Drug Evaluation Unit (NCDEU) 52nd Annual Meeting. Presented May 20, 2012.

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