George Clooney (Gained 35 Pounds)
Credit: Everett

Clooney packed on 35 pounds (we're not sure how much of that was from the beard) to play a CIA operative in Syriana, then won a best supporting Oscar and a Golden Globe for the role. "[M]y job was just to eat as fast as I could, as much as I could," explained the actor, adding, "But mostly you just ate until you wanted to throw up, and made sure you didn't throw up. So that was my job for a month, was eating."

The Bottom Line:
Clooney injured his back during filming, and he's lucky he didn't hurt anything else. "Weight gain causes wear and tear" on the joints, says Kushner, who compares the experience to carrying, say, a 40-pound backpack. "If you have bad knees going into it, your knees are not going to feel better, they're going to feel worse."