Michael Fassbender (Lost 42 Pounds)
Credit: Everett

In 2008's Hunger, Fassbender played Bobby Sands, a young prisoner who led the second Provisional Irish Republican Army hunger strike in 1981 and died after 66 days without food. Off-screen, Fassbender went on a fast of his own: The combination of a 900-calorie-a-day diet plus exercise (skipping, yoga, walking) resulted in about a 42 pound weight loss. "It is such a psychological prison," he's said of the process. His final weight: A reported 127 pounds.

The Bottom Line:
Theoretically, Fassbender was losing weight in a recommended way – by reducing his caloric intake and exercising. But he took it to an extreme. "You shouldn't be taking weight off in starvation mode," says Kushner.