Yeah he was fasting during training camps when he became a religious zaelot and his " Rasputin " was with him even during the camps...
Sergei commented on it, back then, saying it was impossible to fast like that and be anywhere close to 100%..
He indeed looked buffer and way better against Monson, Ishii and especially Rizzo where his fierceness ( and GnP ) almost looked like a prime Fedor's one...
Source or GTFO
Ive heard him fasting for a day or while doing that cold water ritual in winter.
Never heard anywhere that he was fasting during training.