Obese people often say they'd like to eat less but feel almost powerless to stop indulging, and now new research suggests that explanation might be all too true.
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 quickly gained lots of weight. 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 their foot if they did so.
Meanwhile, rats fed 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 foot 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.
"They went into voluntary starvation," said study author Paul Kenny, an associate professor at Scripps Research Institute in Jupiter, Fla.
So what might this say about human behavior?
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 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 that they feel compelled to seek out more and more junk food.
The findings were published online March 28 in Nature Neuroscience.