What happened to Brando between 1968 and 1972?
In '68 he costarred in The Night of the Following Day. He was young and thin with an athletic build. In '72, just four years later (check my math), he starred in The Godfather, where he was old and fat.
I know in The Godfather he put cotton balls in he mouth to give the sound he wanted and that would make he checks puff but I think he was genuinely out of shape.