But 300 calories is a large portion, so the researchers decided to do a similar study but with smaller (100-calorie) portions as well as the large portions. In addition, a third group of women consumed no snack calories. The study included 31 obese and 27 non-obese women.
All participants were asked to "work" for their food by performing tasks on a computer program set up as a sort of slot-machine. When all of the shapes on the screen matched, volunteers earned points toward eating.
The women were given pre-packaged portions of their favorite snack to eat every day for two weeks. Snacks tended to fall into one of two categories: high-fat and high-sugar (cookies, candy bars) or savory, meaning just high in fat (such as potato chips).
"For the zero and 100-calorie portions, the obese and non-obese groups looked the same," Temple said. "The food reinforcement didn't change before and after the two weeks, which would be expected."
However, non-obese women who snacked on 300-calorie portions exhibited no increase in motivation to eat, but motivation did increase in obese women who consumed the larger portion, the study found.
"They actually worked harder for the food," Temple said. "This was surprising to us. We had anticipated in the beginning that we might not see a decrease or as large of a decrease, but we didn't expect to see an increase."
In some cases, women reported still wanting the food even though they didn't like it.
The pattern is strikingly similar to that seen in drug addicts.
"We're exploring this idea of sensitization, which happens with drug use," Temple said. "Response to a drug will actually decrease over repeated use."
And that leads to more drug use.
"I stop short of calling overeating an addiction," she added. "I don't think it has all of the same properties, but I think we can learn something
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