Whenever I play long tournament games, I find that I drink simply enormous amounts of water, far more than my typical rate in daily life (and maybe even more than when I am unusually physically active). I don't do this deliberately, or with any purpose in mind; it just seems that my body desperately seeks hydration when I play chess. I know that some famous players swear by particular drinks during games, e.g. Boris Gelfand during his recent match with Anand talked about an energy drink that he always has in his thermos, and Magnus Carlsen seems to keep plenty of OJ around:
More generally, what I'd like to get here is this:
Pointers to any studies concerning the advantages or disadvantages of the consumption of particular foods or drinks during sustained, concentrated mental activities or competitions like chess (but not necessarily chess).
One interesting read I stumbled on is FM Mike Klein's article "The Grandmaster Diet," which references some scholarly studies related to this matter, as well as items such as a survey by Roberto Baglione of the nutritional habits of 72 GMs and WGMs, which includes anecdotes like the following:
"[GM John Fedorowicz] won’t eat a meal if he cannot complete it at least two hours before a game (according to Fedorowicz, GM Walter Browne used to advertise a free steak dinner to his opponent, with the caveat it had to be eaten right before the round). ... Fedorowicz almost always shuns food during games as well, though he did confess to eating a piece of cheese during a seven-hour round at a U.S. Championship several years ago.
I'd appreciate pointers to any other reliable sources that touch on this general topic of food and drink consumption during activities like chess.