Here's a look at six celebs who lost a shocking amount of weight.
The Hangover star's dramatic weight-loss first made headlines in October when the once-portly comedian showed up to the screening of Birdman, on the closing night of the New York Film Festival, having gone down a few clothing sizes.
His new, slimmer look also surprised people when he was featured in the opening of the 2015 SAG Awards. It's estimated that Galifianakis may have lost as much as 50 pounds.
The Prisoners star famously dropped 30 pounds for his role as the deranged freelance crime photographer Louis Bloom in the Oscar-nominated thriller Nightcrawler. Gyllenhaal, who has been described as a method actor, told ET of his Nightcrawler character, "I could feel that he needed to be hungry, you know, and I wanted to explore that idea."
It wasn't just his diet that changed, but his exercise habits as well. The 34-year-old actor said that he thought of his character like a starving coyote, or a predator. That’s how he found his motivation: "Over time I started running a lot… Coyotes run a lot, and I just started doing that."
The Interstellar star's transformation for his Oscar-winning role in Dallas Buyers Club will go down as one of the most dramatic physical changes ever made for a film. The 45-year-old actor is said to have lost over 50 pounds to get down to the weight required to play the lead character, Ron Woodruff.
In an interview with ETonline, he revealed that the process was rewarding, saying, "It was big transformation … it was a damn spiritual cleanse, man… [but] you're reminded how often you think about the next meal through the day."
The rapper-turned-actor went from 214 pounds down to a staggering 160 pounds for his on-screen turn as a cancer patient in the 2012 drama All Things Fall Apart.
According to 50 Cent, he lost all of the weight in only nine weeks, and was able to do so by running on a treadmill for three hours every day and consuming an all-liquid diet.
The comedian dropped a whopping 80 pounds to get in shape for his role as host of The Price is Right when he took over for Bob Barker in 2007. According to the 56-year-old actor, he shed the weight by getting rid of carbs and drinking nothing but water.
When Carey competed on Dancing With the Stars in April 2014, ET caught up with him during rehearsal where he revealed what he ate during practice to stay fit and get even healthier: " "I eat very clean… I bring a protein bar, my little thing of fruit, and I just drink water."
This Oscar-winning star may very well be the king of physical transformations. He's been known to yo-yo between starving himself for roles that require him to look sickly (The Fighter), and putting on weight or muscle for roles that demand he be overweight (American Hustle) or ripped (The Dark Knight).
The 40-year-old performer's most extreme transformation came when he lost 60 pounds for his role in the 2004 thriller, The Machinist. The six-foot tall actor, who has previously got into amazing shape for his role in the 2000 thriller American Psycho, dropped down to just 122 pounds.
What's even more shocking is the star had to put back on over 60 pounds of muscle in just under six weeks to begin shooting Batman Begins, and ended up putting on nearly 40 additional pounds of muscle during the production.