A research team supervised by Angelo Tremblay of Universite Laval in Quebec, Canada, measured the spontaneous food intake of 14 students after each of three tasks -- relaxing in a sitting position, reading and summarizing a text and completing a series of memory, attention and vigilance tests on a computer, the researchers reported in the journal Psychosomatic Medicine.
After 45 minutes at each activity, the students were invited to eat as much as they wanted from a buffet.
Even though the researchers had already determined that each session of intellectual work required only three calories more than the rest period, the students spontaneously consumed 203 more calories after summarizing a text and 253 more calories after the computer tests, the researchers said.
Blood samples taken before, during and after each session revealed the intellectual work caused much bigger fluctuations in glucose and insulin levels than rest periods.
"These fluctuations may be caused by the stress of intellectual work, or also reflect a biological adaptation during glucose combustion," hypothesized Jean-Philippe Chaput, the study's main author.
The body may spur food intake to restore its glucose balance, the only fuel the brain uses, he said.
"Caloric overcompensation following intellectual work, combined with the fact that we are less physically active when doing intellectual tasks, could contribute to the obesity epidemic currently observed in industrialized countries," Chaput said.