During the 1984-1985 Karpov-Kasparov match, what was Karpov's initial weight? When discussing whether chess is a sport, I have often used that Karpov lost a reported 22 pounds (10 kg.) during the match as a point to show that chess can be physical. While 22 pounds is significant, I think it is even more significant because Karpov was a man with a very slight stature, meaning it was a much higher percentage of his total weight than if he had been a 250-pound man, but nowhere have I ever been able to find what his initial weight was.

Does anyone know Karpov's initial weight at the start of that match, or even his final weight, which would also tell us that information?

Here is one such story.
That's a lot, if validated. Karpov was rather slight at the time, something around 60kg or less, so that represents something under 20% of his body weight.

And actually, that's consistent with other facts, given that was a 50+ game match. Fabiano Caruana says he can drop around 10% of his body weight during a difficult tournament. (Said to an ESPN reporter.) Robert Sapolsky, a Stanford researcher, has measured some players at burning 6000 calories per day in a tournament.

Another unverified data point is Rustam Kasimdzhanov losing 17 pounds at the 2004 championship.

A lot was made of this recently, made "sexy" because Magnus Carlson sought the advice of Olympic trainers for his physical conditioning, but it's not a new discovery. Petrosian would also drop a lot of weight during the championship match cycle, and other champions like Botvinnik and Spassky made getting in physical condition an important part of their match preparation.

ESPN, NPR ("The Chess Grandmaster's Diet"), Men's Health, seems like every magazine got in on it last year.

I don't have anything verifiable on the Karpov bit, but the other work I've seen, taken with the comment from Caruana, means I'll accept it as true until someone can disprove it. It's been verified to happen to players other than Karpov, so why not him?