To see how strong the drive to eat junk food was, the researchers exposed the rats to a foot shock when they ate the high-fat food. Rats that had not been constantly exposed to the junk food quickly stopped eating. But the foot shock didn't faze rats accustomed to the junk food -- they continued to eat, even though they knew the shock was coming. "What we have are these core features of addiction, and these animals are hitting each one of these features," Kenny says. These reward pathway deficits persisted for weeks after the rats stopped eating the junk food, the researchers found. "It's almost as if you break these things, it's very, very hard to go back to the way things were before," Kenny says. When the junk food was taken away and the rats had access only to nutritious chow (what Kenny calls the "salad option"), the obese rats refused to eat. "They starve themselves for two weeks afterward," Kenny says. "Their dietary preferences are dramatically shifted." Scientists are interested in determining the long-term effect of altering the reward system. "We might not see it when we look at the animal," says obesity expert Ralph DiLeone of Yale University School of Medicine. "They might be a normal weight, but how they respond to food in the future may be permanently altered." Related Links: |
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