The difference in the grandmaster situation is that their extreme focus on chess completely displaces their hunger, hunger which needs real estate in your attention to be effective, just like any other felt sensation. And this focus lasts for the majority of the tournament, months. This is different to most people. When you have an immersive job you can get in the zone for many hours of the day, but you do stop working, and your hunger returns.

The closest thing I ever experienced to what they are describing was when I played the game Civilization for the first time in ‘93. I was so obsessed I played it for three days straight, night and day, before I took my first nap. The fluid drained from body, I looked like a skeleton with black holes for eyes. I also did not eat, I remember literally running to the store to get a single can of coke otherwise I just drank water from the bathroom faucet because it was next to my room. Within five days I had easily lost a couple of pounds of bodyfat.

Having played chess competitively throughout school, it’s no surprise chess Grandmasters have this total level of focus in tournaments.