The researchers had already shown 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% and 29.4 % 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. “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 could be reacting to these fluctuations by spurring food intake in order to restore its glucose balance, the only fuel used by the brain.

Have I told you that last year I basically spent something like seven months sitting on my butt figuring out incredibly tricky and important things, and got really fat?

http://www.eurekalert.org/pub_releases/2008-09/ul-iwi090408.php