The researchers found that, for the rats being fed junk food, the pleasure centers in the brain became less responsive to the tasty high-fat food as time went by, requiring more and more junk food to stimulate the brain's pleasure centers. Consequently, the rats began to eat compulsively, taking in twice as many calories as the other group, and soon became obese.
For years, I've plotted my weight on a graph every morning. I have the illusion that graphing helps me control my eating, although I know it doesn't really. But it does help me see trends. For example, I know I'm always heaviest in winter. That's because I eat all day long in winter! When it's cold, I especially crave sweet and high-fat foods, and if junk food is available, I'll eat it.
Photo by Sebastian Dooris (Flickr).
As Addictive as Heroin
I should lay off the junk food, though. Scientists at Scripps Research Institute have shown that rats fed a steady diet of high-fat junk food develop addictive behavior similar to heroin addiction! Sure they're rats, but rats are mammals just like we are, and their brain physiology is far more similar to ours than it is different.
The rats in the study were divided into two groups. One group was fed a healthy diet of high-nutrient, low-calorie chow. The other group was given unlimited amounts of junk food, which included Ho Hos (packaged cakes), bacon, cheesecake, pound cake and sausage.
The two researchers found that, for the junk-food rats, the pleasure centers in the brain became less responsive to the tasty high-fat food, requiring more and more food to stimulate the brain's pleasure centers. Consequently, the rats began to eat compulsively, taking in twice as many calories as the other group, and soon became obese.
Five days to Loss of Control
Habituation to the high-fat diet was surprisingly fast. After only five days on the junk-food diet, the rats showed "profound reductions" in the responsiveness of their brains' pleasure centers. At this point, the rats "lose control" of their eating, said researcher Paul Kenny of Scripps. "This is the hallmark of addiction."
As another way to assess the impact of junk-food on the rats' brains, the scientists used electrodes to stimulate the pleasure centers in the brains of both groups of rats. The rats could control the amount of pleasurable stimulation by running on a wheel. The more they ran, the more pleasurable stimulation they felt. During this part of the experiment, the rats that were addicted to junk food ran more than the healthy-diet rats, suggesting that they needed more stimulation of the pleasure center to feel good.
Addiction May Be Permanent
So what happened when the junk-food addicts were forced to go cold turkey and give up the cakes and bacon? The addictive changes in the brain persisted for weeks, even after the rats' weights returned to normal. In presenting their data at the Society for Neuroscience Annual Meeting, scientists Paul Kenny and Paul Johnson speculated that the addicted rats' response to food may be changed permanently.
Ack! Well then, maybe it's a good thing my husband forgot the chips at the grocery this week.
For real, I plan to keep in mind the five days to food addiction reported by these guys at Scripps, and try to get a grip on my junk-food-fests this winter.
This study was published in the journal Nature Neuroscience.
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