Dr. Jean-Philippe Chaput of the University of Copenhagen speculates that mental stress from computer work triggers changes in blood sugar levels that trick the brain into thinking it has worked off calories that need replacing.  This in turn increases an appetite for sweet treats like chocolate.

This all started when Dr. Chaput noticed a supervisor regularly snacking on chocolate when doing computer work.  He then asked one group of female students to go to a computer and start working while another group was told to relax for 45 minutes.
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