11 Sep 2008
Researchers found the stress of onerous mental tasks caused subjects to overeat.
The results may help suggest how modern lifestyles have contributed to an obesity epidemic.
The research team, supervised by Dr Angelo Tremblay, measured the spontaneous food intake of 14 students after each of three tasks.
The first was relaxing in a sitting position, the second reading and summarizing a text, and finally completing a series of memory, attention, and vigilance tests on the computer.
After 45 minutes at each activity, participants were invited to eat as much as they wanted from a buffet. The researchers had already calculated that each session of intellectual work requires only three calories more than the rest period.
However, despite the low energy cost of mental work, the students spontaneously consumed 203 more calories after summarizing a text and 253 more calories after the computer tests.
This represents a 23.6 per cent and 29.4 per cent increase, respectively, compared with the rest period.
Blood samples taken before, during, and after each session revealed that intellectual work causes much bigger fluctuations in glucose and insulin levels than rest periods.
Jean-Philippe Chaput, the study's main author, said: "These fluctuations may be caused by the stress of intellectual work, or also reflect a biological adaptation during glucose combustion."
The body could be reacting to these fluctuations by spurring food intake in order to restore its glucose balance, the only fuel used by the brain.
Mr Chaput added: "Caloric overcompensation following intellectual work, combined with the fact we are less physically active when doing intellectual tasks, could contribute to the obesity epidemic currently observed in industrialised countries.
"This is a factor that should not be ignored, considering that more and more people hold jobs of an intellectual nature."
The results of the study, carried out at Université Laval in Quebec, Canada, are published in the most recent issue of Psychosomatic Medicine.