The 26-year-old actor said he hated the process of gaining weight because he had to wake up in the night just to drink protein shakes, the Daily Mail reported.
"Once Tom Hardy got cast, he's a big boy and it became, 'Are we from the same fabric of man, can I be your brother?' Standing next to him I felt like Josh Groban, I just felt very meek," LaBeouf told Jay Leno while promoting the film.
"I gained about 40lbs, just eating, your whole lifestyle becomes something else. Every three hours you consume, food becomes vitamins, it's about necessity, which is gorging, it's horrible. It was protein shakes really, a lot of chicken and eggs.
"At night, you wake up every three hours, take the shake and wake up. It's monotonous. You only have a certain amount of time, I had a month, two months to get there," LaBeouf said.