SlashFilm posted this graphic of the many physical transformations that Christian Bale has gone through for various roles he has played over the years. He hasn't needed Jenny Craig to help him lose weight for a role when duty called. Lordy, he was practically a skeleton in The Machinist.
The only other notable role missing was how he looked in American Psycho.
His character obviously found time, in-between violently murdering people, to get to the gym regularly.