In The Martian, Matt Damon finds himself once again stranded on a planet alone. But unlike his character in Interstellar, who resorts to cryogenic sleep to stay alive, Damon in The Martian is forced to be inventive and resourceful in order to survive the years he’s going to be on Mars before anyone from Earth can get to him for rescue. One way he does this is by growing his own food, potatoes, on which he is forced to sustain for his indefinite future. Eating so little would obviously take a toll on anyone, and by the end of his stay on the planet Damon has lost a shocking amount of weight. But did he undergo the transformation for real?
When Matt Damon gained 30 pounds (is 30 the magic number?) for The Informant, he decided to just enjoy the experience. “There was just more of me to love! She [wife Luciana] was a good sport about it. We had fun. I loved parading around in my belly. And my stepdaughter thought it was really fun, too—that I got all squishy.”
According to an interview with Damon, it sounds as if the actor wanted to shed the pounds, but director Ridley Scott forbade it. “I talked to Ridley about [losing weight for The Martian] because I’ve lost weight before for movies,” Damon told Newsweek. “We had about six months. And I said, ‘That’s perfect. I’ll lose about 30 or 40 pounds, and we’ve got to shoot all that stuff first.’ And he went, ‘F*ck that.'”
Judging by Scott’s reaction, I’m guessing Damon kept his weight intact throughout the movie, so how did he appear so skinny? A likely explanation is that the movie used CGI to alter Damon’s appearance. The technique is being used more and more often these days to alter actors’ bodies, and was famously put to use in Game of Thrones‘ Season 5 finale for Cersei Lannister’s non-nude nude scene. But the effect has been used numerous other times as well, and here are some examples.