The 30-year-old spoke to People magazine at Monday's "Man of Steel" premiere and said it was "a very, very long and involved process."
To maintain his Kryptonian bod, the actor says he went through "a horrible eating phase" in which he significantly "leaned down." He called the process "exhausting."
According to the strong-jawed star, before he began shooting the Superman epic, his diet consisted of 5,000 calories a day, and once he landed the role of Kal-El, that number was cut to 2,500. But, he's not mad about it, because as he put it, "it was hard but it paid off."
As you may imagine, Cavill went all-out once his strict diet was over.
"I had an apple pie," he said, "a tub of ice cream and a full pizza."