Yeah, Matango was a film from Japan (Toho, same guys who did Godzilla and Super Sentai), basically a bunch of people are shipwrecked on a mysterious island and forced to subsist on mushrooms which turn them into fungus men. IIRC it ends with the last human returning to the mainland and changing shortly thereafter.
Also, what a massive asshole this guys is; He knocks his wife unconscious and then force feeds her the monster fruit? He could have at least waited till she had woken up, explained the situation, and let her make the choice herself.