Does Thinking Make Us Fatter?

Angelo Tremblay noticed something odd every time he worked up a grant application for his research program in a Quebec university. He had a craving for chocolate chip cookies.

Now, thanks to research in his lab at the Universite Laval, he has a better understanding of why. It turns out that performing mental tasks, like trying to solve problems while working at a computer, stimulates the appetite so much that people tend to eat significantly more calories than they burned while performing the "knowledge-based" tasks.

In a study published in the current issue of Psychosomatic Medicine, researchers found a physiological basis for the spike in appetite. Mental work "destabilizes" the levels of insulin and glucose, two critical components in the body's regulatory and energy machinery, thus stimulating the appetite, said Jean-Philippe Chaput, lead author of the study.

"The brain uses only glucose for energy," unlike the "muscles, which use fat and glucose," Chaput said in a telephone interview. So when the level of glucose, or sugar, becomes unstable, the brain demands more.

According to the research, participants consumed far more calories after performing mental tasks than they consumed after relaxing for the same period of time.

The study is quite small, involving only 14 women, so the results are only tentative, but Chaput said he and his fellow researchers have already embarked on a larger study involving 50 men and 50 women. Only women were used in the pilot study because it has been well established that men and women react differently to stress, and the researchers did not want to cloud the results.

At this point, however, the study indicates that a rapidly changing lifestyle toward "knowledge-based work," like time spent at the computer or trying to solve mental challenges, may be a significant factor in the current obesity epidemic, Chaput said.

"There are a lot of people doing this kind of work now, compared to physical work in the past, so we postulate that it can explain in part" why so many people in so many countries are getting fat, he said.

As the researchers put it in their paper, "knowledge-based work represents the main working modality in a context of modernity." In other words, many are spending fewer calories, but taking more in, because of changes in the work environment.

That's true not only in the world of employment, but in the world of entertainment as well. Many people are spending more time playing computer games, some of which can be intellectually challenging, than playing tennis, for example.

The researchers are members of the university's department of medicine, and they specialize in kinesiology, the mechanics and anatomy of human movement. The 14 women in the study were all students, ranging in age from 20 to 30 years. All were in good health, with no eating disorders, normal weight, and free of food allergies.

During a two-month period they were each required to participate in three 45-minute exercises consisting of relaxing in a chair, reading a document and writing a summary of 350 words, and "a cognitive task consisting of a comprehensive battery of computerized tests."

Each participant was tested separately from the others.

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