Theron was tasked with putting on a bunch of weight and muscle in order to accurately depict the serial killer Aileen Wuornos in the movie Monster. Theron was asked to put on 30 pounds over the course of one month. She did this by eating mostly carbohydrates and sugar to mimic the diet of Aileen Wuornos.
The Monster Within
Theron managed to pull this transformation off in the nick of time. In addition to changing her diet, Theron also began smoking cigarettes and drinking liquor daily to get her into the mind of Aileen Wuornos. This ended up working out for her, and she was awarded an Oscar for her depiction.