Source: ESPN - Link
The 1984 World Chess Championship was called off after five months and 48 games because defending champion Anatoly Karpov had lost 22 pounds. “He looked like death,” grandmaster and commentator Maurice Ashley recalls.
In 2004, winner Rustam Kasimdzhanov walked away from the six-game world championship having lost 17 pounds. In October 2018, Polar, a U.S.-based company that tracks heart rates, monitored chess players during a tournament and found that 21-year-old Russian grandmaster Mikhail Antipov had burned 560 calories in two hours of sitting and playing chess – or roughly what Roger Federer would burn in an hour of singles tennis.
A fascinating look at stress in the chess world. There is also research that shows that the brain burns a significant number of calories during periods of intense focus, but that’s not the main factor here.