> While I've read that there's not a lot of difference between just chilling and thinking of some hard problem

I find that difficult to reconcile with chess grandmaster calorie consumption.

https://www.npr.org/2019/09/18/762046422/the-chess-grandmast...

> Polard, this company that tracks heart rates, monitored chess players during a tournament and found out that this 21-year-old Russian grandmaster, Mikhail Antipov, had burned 560 calories in two hours, which we found out was roughly what Roger Federer would burn in one hour of singles tennis.