That hardly seems conclusive. For example,

> Meanwhile, players also eat less during tournaments, simply because they don't have the time or the appetite. "The simple explanation is when they're thinking about chess, they're not thinking about food," says Ewan C. McNay, assistant professor of psychology in the behavioral neuroscience program at the University of Albany.

That seems far more likely. I'm sure many of us can relate to working through lunch when we have an intense deadline, and not even realizing we're hungry until hours later.

> According to Ashley, India's first grandmaster, Viswanathan Anand, does two hours of cardio each night to tire himself out so he doesn't dream about chess; Kasimdzhanov drinks tea only during tournaments and plays tennis and basketball every day. Chirila does at least an hour of cardio and an hour of weights to build muscle mass before tournaments.

And apparently they're exercising quite a lot as well.

This hardly seems to support that it's just brain power. And my recollection is that focus does not significantly increase glucose uptake in the brain - though stress can obviously increase heart rate, but that's separate, one can focus without being stressed.

If thinking hard required a lot of energy, wouldn't we expect that thinking hard would cause an increased heart rate and faster breathing?