Rob McElhenny (Gained 52 Pounds)
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Unlike the rest of the guys on this list, the It's Always Sunny in Philadelphia star played his intentional 52-pound weight gain for laughs. Though he tried to fatten up with healthy chicken breasts, rice, and vegetables, he eventually realized Big Macs and doughnuts were an easier way to suck down 1,000 calories per meal. His big complaint: "My legs and my gut got so big that my penis looked even smaller."

The Bottom Line:
Even a sedentary guy his age should only be consuming 2,400 calories per day, according to the USDA. Along with the potential health risks of high blood pressure and high blood sugar, the actor also could have ended up with stretch marks. "If your skin is highly resilient it will come back with no stretch marks at all," says Kushner. "But if you're a little older, your skin may lose its elasticity and not have the resilience you need."