good question
How many calories in hour chess consume?
Well, the brain activity consumes appr. 20% of your energy. If you play chess intensively, you consume 20% of physical intense activity.

I was watching agadmator's YouTube channel as he covered the Carlsen / So match at Fischer Random. It appears they had heart monitors on the players so that their anxiety and stress levels could be assessed. In the last two games, as So was closing in on beating Carlsen, his heart rate was between 140 and 161 bpm. (Carlsen's was about 85).
I don't even hit 161 when I'm running full-out during a stress test.
So how many calories was So consuming? I'm guessing quite a few.
What you think? More than just sitting and moving your hands? Does't using your brain consume quite a lot energy? Is chess effective fit sport? I example sweat often because of stress.