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December 7, 2009
Restricting Sugary Food May Lead to Overeating
Many people try to lose weight by periodically forbidding themselves from eating certain foods. But depriving yourself of tasty food can backfire, new research in rats suggests. It can activate the brain's stress system, causing anxiety and withdrawal-like symptoms, and leading you to overeat the forbidden foods when you get a chance.
Much of the research on overeating has focused on food's pleasurable effects, which scientists call positive reinforcement. A team of researchers led by Dr. Pietro Cottone and Dr. Valentina Sabino at the Boston University School of Medicine and Dr. Eric Zorrilla at the Scripps Research Institute wanted to explore the role of negative reinforcement. That's the idea that the stress of not having certain foods might drive dieters to overeat those foods once they become available.
The researchers recently found that rats given intermittent access to sugary food ate less of their normal food when the sweet food wasn't available, and they overate the sweet food when it was available again. The scientists hypothesized that the brain's stress system might be behind the behavior. Funded by several NIH institutes, along with the Ellison Medical Foundation and the Pearson Center for Alcoholism and Addiction Research at Scripps, the team—which included NIH researcher Dr. Kenner C. Rice—set out to investigate.
The scientists tested a drug that blocks the action of corticotropin-releasing factor (CRF), a signaling molecule involved in the brain's response to fear, anxiety and stress. CRF has been tied to withdrawal syndromes for every major drug of abuse, including alcohol, nicotine, cocaine, opiates, amphetamines and marijuana.
The team divided 20 rats into 2 groups. One group was fed alternating diets of 5 days of regular chow and 2 days of sweet chow. The other was given only regular food. All rats could eat as much as they wanted. After 7 weeks, the rats were given the CRF-blocker.
The researchers reported on November 24, 2009, in Proceedings of the National Academy of Sciences that blocking CRF blunted the rats' bingeing. The diet-cycled rats ate more of the regular chow and less of the sweet food when it was available. The drug had no effect on the rats eating only normal chow. The drug also blocked the diet-cycled rats' anxious behavior when their sweet food was withdrawn, without affecting control rats.
To explore where CRF was at work, the team measured CRF levels in the central amygdala, a brain area involved in fear, anxiety and stress responses. Diet-cycled rats had significantly higher CRF levels when eating normal chow. Their levels were normal when the rats were fed sweet food. These results show that withdrawal from tasty food, at least in rats, leads to an increase in stress.
"People will often say they are eating bad foods or fail a diet because they're stressed," Zorrilla says. "Our findings suggest that intermittently eating sweet food changes the brain's stress system so that you might feel stressed…In other words, you might be self-medicating stress-like symptoms of abstinence with that piece of pie."
"The findings suggest that frequent dieting with frequent relapse is worse than dieting by itself," Cottone says. On and off, yo-yo dieting may actually be a risky habit.
—by Harrison Wein, Ph.D.