The researchers used 155 rats to measure the neurobiological responses. The first group, the diet cycled subjects, repeatedly ate standard rat chow for five days, followed by a highly palatable, high-sugar, chocolate-flavored chow for two days.
The second group ate only standard food. The amount of food consumed was not restricted for either group. When the diet-cycled rats were fed standard chow, they showed less motivation to obtain it, refused it, although it was previously acceptable, and they exhibited anxiety. However when the rats resumed eating the palatable food, they overate and their anxiety-related behaviors returned to normal.
The researchers then looked at the role of the brain's stress system, which contributes to cycles of drug and alcohol binging and withdrawal, in driving these behaviors. They found that during abstinence from palatable foods, the rats showed increased corticotropin-releasing factor (CRF) gene expression and peptide in the amygdala, an area of the brain involved in fear, anxiety and stress responses.
Similar to the anxiety, only when the diet-cycled group was fed palatable food did CRF levels return to normal. Importantly, the blockade of the CRF receptor 1 with a selective antagonist was able to prevent all the behavioral outcomes of palatable food withdrawal.
According to the researchers, CRF is a key stress neurotransmitter. "In observing the activation of the amygdaloid CRF system during abstinence from palatable foods, we understood the causes of recurrent dieting failures," said study co-author Pietro Cottone, PhD, an assistant professor and co-director of the Laboratory of Addictive Disorders at Boston University
"CRF activation during abstinence from palatable foods induces a negative emotional state which is responsible for signs of anxiety and contributes to relapse to 'forbidden foods,'" added study co-author Valentina Sabino, PhD, an assistant professor and co-Director of the Laboratory of Addictive Disorders in the Department of Pharmacology and Experimental Therapeutics at Boston University. "The stress experienced by frequent dieters in abstinence from palatable food has neurobiological similarities to the negative emotional state of drug and alcohol addicts."
Citation: Pietro Cottonea, Valentina Sabinoa, Marisa Roberto, Michal Bajoe, Lara Pockrosa, Jennifer B. Frihauf Eva M. Fekete, Luca Steardog, Kenner C. Riceh, Dimitri E. Grigoriadisi, Bruno Contid, George F. Kooba, Eric P. Zorrillaa, 'CRF system recruitment mediates dark side of compulsive eating', PNAS Online, doi: 10.1073/pnas.0908789106