The 32-year-old actor may have been cast as hunky Christian Grey in the long-awaited '50 Shades of Grey' movie, but he still feels like a "skinny kid" and wishes he was more muscular.
He said: "I don't like my physique. Who does? I was a skinny guy growing up, and I still feel like that same skinny kid."
Jamie also admitted he never feels comfortable in a suit - something which initially made getting into character for the movie quite difficult.
Talking about his discussions with director Sam Taylor-Johnson, he added to Interview magazine: "I think there was so much more to Christian that we covered--someone who is careful to keep himself in shape, someone who spends obscene amounts of money on presenting himself.
"A lot of that work was done in the gym and with costume. We didn't talk about particulars of the way he would move.
"But I'm quite awkward in a suit because I don't have an opportunity to wear a suit very often, and this is a guy who lives in a suit--the best suit."
However, the actor admits he is now much more at ease in formal wear thanks to spending so long working on the movie.
He added: "That has to have an effect. But when you end up in a suit for 80 percent of the filming process, you become pretty comfortable with it."