"It was hard, but it paid off," the actor says of the road to physically becoming Superman

Credit: Gilbert Carrasquillo/FilmMagic

You don’t become Superman overnight.

“It’s a very, very long and involved process,” Henry Cavill told PEOPLE at Monday’s Man of Steel premiere in New York – the movie opened nationwide Friday – about his exhausting physical transformation from human to superhuman.

It went in stages. And all of them were painful.

“Five months before shooting there was varying stuff which ended up being mass building and then leaning down,” said the actor, 30. “Throughout the shoot it was just waking up and making sure I got an hour in [of exercise] before I went to work.”

He was then forced to go through “a horrible eating phase where we really, really leaned down. It was exhausting.”

“They didn’t force me to give anything up,” he said. “They just cut my calories right down to 2,500 [a day]. And keep in mind, only a few months ago I’d been up to 5,000. So it was a big drop.”

He added: “It was hard but it paid off.”

So, what was the first thing he ate after the brutal process was finally over? “I had an apple pie,” he said, “a tub of ice cream and a full pizza.”

Reporting by MICHELLE WARD