Could thinking make you fat? Maybe. A small Canadian study has found that people eat more after an intellectual exercise than they do after just sitting quietly for the same amount of time.

The scientists had 14 female students engage in three 45-minute sessions before being invited to eat as much as they wanted at a buffet. For one session, they rested in a sitting position. In the next, they read a document and wrote a summary of it, and in the third they performed a series of computer-based tests.

Even though the same amount of physical energy was involved in all three sessions, the women consumed an average of more than 25 percent more calories after the intellectual exercises than after just sitting quietly. The study, published in Psychosomatic Medicine, controlled for habitual diet, body mass, anxiety level and other factors.

There may be a physiological explanation. In blood samples drawn periodically during the experiment, the researchers found an increase in levels of the stress hormone cortisol and increased fluctuation in plasma glucose and insulin levels during and after the mental workouts.

“There is nothing in these findings that can be described as restful activity,” said Angelo Tremblay, the lead author and a professor of nutrition at Laval University in Quebec City. “We may sometimes be inclined to underestimate the biological impact of mental work.”

—The New York Times