It’s not just actors like Robert De Niro (Raging Bull) and Christian Bale (The Machinist) who have taken physical transformation beyond ‘just’ makeup.
It’s one thing wearing a prosthetic nose or a fat-suit or dying your hair. I’d guess it’s pretty shocking having your head shaved as so many actresses have done, but at the end of the day theres a wig to go home in and it soon grows long enough to add hair extensions. But messing with your body weight is a big deal. Not just the time it takes to get it back but the cases where it’s been associated with subsequent eating disorders (eg Toni Collette and Kyra Sedgewick).
One of the most extreme recent examples is Daniel Sánchez Arévalo’s Gordos which required such a range of weight gains and loses from its cast that it had to be filmed in segments over some ten months.
But the Columbian movie Sin Tetas No Hay Paraiso probably wins the prize: asking its star to have breast implants and showing the procedure on-screen.