I agree this is absurd on its face. However - one could make the argument that some supplements (natural) can increase higher brain functions - including cognitive ability and memory.
http://www.ajcn.org/cgi/content/full/71/6/1669S#SEC4
(Read the conclusion regarding adult brains)
Now no player needs steroids to lift the pieces and move them - but one could say that intaking substances for the purpose of enhancing your mental ability could be considered "cheating" unless it was something everyone could do - which in this case - it would be.
If they want to regulate how much vitamins A, B6, B12, and C a person has - thats lame.
The game of Kings was meant to be a contest of the mind - a strategic battle without the blood. If they do this - they might as well not allow a player to jog or physically "warm up" as some players do - as the increased respitory and circulatory rates would give them an "advantage".
However - I will say this - the brain is a muscle like any other in one way - if you fail to use it - it will atrophy.