Does Thinking Make Us Fatter?

Each "came into the lab at 8 a.m., and we gave each participant a standardized breakfast," Chaput said. "After that we started the exercise at 10:30 a.m., one participant at a time, and they came every two weeks. At about 11:30 a.m. we gave them a buffet type of meal, comprising a lot of food."

The food in the buffet was weighed and analyzed before and after the lunch, so researchers knew precisely how much and which type of food each participant had eaten. Various tests during each exercise also told the researchers precisely how many calories the participants were burning at the time.

The participants burned only about three calories more during each of the two "knowledge-based" experiments than during the 45 minutes when they rested in a comfortable chair. So the caloric expenditures were relatively quite low for mental tasks compared to the period spent relaxing.

But the intake was significantly higher. Participants consumed 203 more calories after the reading experiment, and 253 more calories after the computer tests, than the resting participants. That's an increase of 23.6 percent and 29.4 percent, respectively.

Measurements of glucose and insulin became quite erratic during the mental tests. Glucose soared almost immediately when the participants were reading and then dropped dramatically. It dropped and remained below normal during the computerized tests. Insulin rose slightly during the reading test, and then dropped, and it dropped steadily during the computer tests.

That erratic performance by both glucose and insulin caused the appetite to rise, apparently in response to a need to restore the energy balance, the researchers conclude.

The results probably would have been different if men had been included in the study, as they will be in future research. That's because mental challenges provoke stress, and it "is expected to be higher in females than in males," according to Chaput. That is also reflected in many other studies. He said women also tend to eat more following stress than men do, although "we don't know why yet."

Although the first study was limited to college-aged participants, Chaput said other research in his lab suggests that the same findings will apply to children as well as to older adults.

But if mental challenges cause people to eat more food, why aren't nearly all college professors fat?

Simple, Chaput said. Eating is only part of the weight control "package," he added. It's possible to spend a lot of time working out problems at the computer if that is balanced with a reasonable amount of time working out, literally.

Some college professors, of course, are fat. Maybe the skinny ones use their computers on the treadmill.

Lee Dye is a former science writer for the Los Angeles Times. He now lives in Juneau, Alaska.

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