In Avengers: Endgame, Tony & Nebula are stuck on Titan and later on the Guardians's spaceship, running out of food and water. During the scene in which he records a message to Pepper and when Nebula puts him on the chair, he looks frail and starving with veins popping and blood shot eyes.
When he returns to earth and has a confrontation with Steve Rogers, he really looks weak and fragile. His face and body looks shrunken from the starvation.
Did RDJ starve himself for this part of the role or was it CGI?
I assume it is easier to make Hemsworth fat by using padding but I don't know how/if CGI can make RDJ look skinny and starved.