The only think I can give you is that I recall recently seeing that grandmasters could burn 6000 calories in a tournament match. That's under extremely high pressure, thinking very hard for hours, but physically just sitting there.<p><a href="https://www.espn.com/espn/story/_/id/27593253/why-grandmasters-magnus-carlsen-fabiano-caruana-lose-weight-playing-chess" rel="nofollow">https://www.espn.com/espn/story/_/id/27593253/why-grandmaste...</a><p>If you don't like that one, Google had several other sources...