New Delhi, July 12 -- LOS ANGELES - By the time Christopher Nolan told him he wanted his Odysseus lean but strong, Matt Damon had already started doing the math. The 55-year-old was being asked to carry the physical weight of one of literature's most enduring wanderers, and he treated that mandate with the same seriousness Nolan brings to every frame he shoots.

The transformation was sharper than it might appear on paper. Damon entered production for The Odyssey weighing between 185 and 200 pounds, his typical working weight across a career spanning roughly 80 films. He finished it at 167. That number represents the lightest he has been since high school, and the weight loss was not the only lasting change the production required.

Damon...