Obese individuals often say they’d like to eat less but feel powerless to stop indulging in foods that many consider to be unhealthy. New research now might support these claims that many people often think is an excuse to overeat. The theory stems from a study in rats. When researchers gave the rats unlimited access to a calorie-laden diet of bacon, pound cake, candy bars and other junk food, the rats’ weight skyrocketed. As they plumped up, eating became such a compulsion that they kept chowing down even when they knew they would receive an unpleasant electric shock to one of their feet if they did so. Meanwhile, rats that were sustained on what would be the human equivalent of a well-balanced, healthy diet — and given only limited access to the junk food — didn’t gain much weight and knew enough to stop eating when they received the cue that a shock was imminent. Even more startling, the researchers report, is that when they took away the junk food from the obese rats and replaced it with healthier chow, the obese rats went on something of a hunger strike. For two weeks, they refused to eat hardly anything at all. The findings were published online in Nature Neuroscience. “They went into voluntary starvation,” said study author Paul Kenny, an associate professor at Scripps Research Institute in Florida. So what might this say about human behavior and addiction? Researchers aren’t certain if the results apply to people struggling with their weight. But they say it’s possible that a diet heavy in highly rewarding foods — quite literally, sausages, cheesecake and other highly processed or junk foods — might cause changes in the brain’s reward system for satiety. When that goes awry, the result is not only that people gain weight, but they feel compelled to seek out more and more junk food. There also could be something in the accumulated fat itself which alters the brain’s reward threshold, setting up a “vicious cycle” of overeating yet not feeling satisfied, said Pietro Cottone, an assistant professor in the Laboratory of Addictive Disorders at Boston University School of Medicine. “The only way to return to normality is probably dieting for a long period of time to lose the body weight and not eating junk food,” Cottone said. This isn’t the first study to find commonalities between the brain’s reaction to cupcakes and illicit drugs. An earlier study by Cottone and his colleagues suggested that weaning rats off a high-calorie diet might lead to similar, though not identical, effects in the brain as withdrawing from drugs and alcohol. Dr. Julio Licinio, director of the John Curtin School of Medicine Research at the Australian National University, called the study answers “one of the many missing pieces in the puzzle of obesity and addiction. Now that it is clear that areas of the brain involved in addiction and also involved in obesity, the next question is: Why do those areas become dysregulated in some people but not in others?” Licinio asked. “And importantly, why do some people who have a biological tendency towards addiction go to drugs, while others go to alcohol, and others go to food?” SOURCES: Paul Kenny, Ph.D., associate professor, department of molecular therapeutics, Scripps Research Center, Jupiter, Fla.; Pietro Cottone, Ph.D., assistant professor, pharmacology and psychiatry, and co-director, Laboratory of Addictive Disorders, Boston University School of Medicine, Boston; Julio Licinio, M.D., director, John Curtin School of Medicine Research, Australian National University, Canberra; March 28, 2010, Nature Neuroscience – Anthony Isaac Palacios