The 17-year-old, who plays werewolf Jacob Black in the Twilight series, admitted that he went up two clothes sizes following a new workout regime for the sequel, People reports.
"I grew out of a lot of my clothes. I went from a men's small to a men's large," he said.
The actor added: "The day I finished Twilight, I came home and started bulking up. For New Moon, I'm 30 pounds heavier than I was in Twilight."