After playing in American Psycho as Patrick batman a rich well shaped business man,lost more than 63 pounds to play in "the Machinist" in 2003.
The producers of the film claim that Christian Bale dropped from about 173 pounds in weight down to about 110 pounds in weight to make this film. They also claim that Bale actually wanted to drop down to 100 pounds, but that they would not let him go below 120 out of fear that his health could be in too much danger if he did. His diet consisted of one can of tuna and an apple per day. His 63-pound weight loss is said to be a record for any actor for a movie role. He regained the weight in time for his role in Batman Begins (2005)
Due to his part in The Machinist (2004), Christian Bale was vastly underweight (about 120 pounds on his 6 foot+ frame) when he was under consideration for the part. After being cast, he was told to become as "big as you could be" by Christopher Nolan. Bale underwent a dietary and exercise regimen and ending up weighing about 220 pounds (about 40 pounds above his normal weight). It was decided that Bale had became too large (friends of his on the film's crew dubbed him "Fatman") and he quickly shed about 20 pounds to have leaner, more muscular frame. Bale gained 100 pounds in 6 months, describing the experience as an unbearable physical ordeal.
Used to it, Bale get down in weight again for Rescue down (2005) in which he lost other 55 puonds. Not to forget at this point performances like "The Prestige" where Bale was still in good shape and the finally contrast between Batman in "The dark knight" and Jonh Connor in "Terminator salvation".
Bale is known as a class A method actor and he got famous also for his perfect way of learning and performing accent through the entire filming, so to make the cast believing of his fake "american" origins.