Simply so, how did Captain America gain weight?
Body double / actor doubling for the entire body.
The body double was English Shakespearean trained stage actor Leander Deeny (who even dieted for the role).
Secondly, who is skinny guy in Captain America? With just two major film credits, the scrawny, English stage actor is a long way from being a household name. But thanks to the magic of CGI, Deeny has one of the summer's most memorable screen roles in “Captain America: The First Avenger.”
Secondly, why does Captain America look so skinny in endgame?
They actually used CGI to put his face on a body that was that skinny. That's why, and it is beautifully and very creatively hidden, he looks the slightest bit odd with his face and that body.
Is Captain America Dead?
Iron Man and Black Widow were the major deaths of the film (on the hero side), but some fans were pleasantly surprised to find that Captain America survives the whole movie. Of course, the shocker is that he's an old man now, but Cap still got an unexpected happy ending.
