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Jonah Hill: July 2006 vs. September 2011

The Oscar nominee went through a serious transformation in 2011. So how did he drop the weight?

"I just woke up one day, and I was like this. It was really cool," the actor teased. “No, I went and saw a nutritionist out here in New York, and I take it seriously. It’s a good decision.”

Eminem: February 2006 vs. July 2015

Eminem has never been one to shy away from his past drug addiction, but in an essay for Men's Journal, the rapper revealed new details about how his pill popping greatly impacted his weight.

"In 2007, I overdosed on pills, and I went into the hospital. I was close to 230 pounds. I'm not sure how I got so big, but I have ideas," the 42-year-old wrote.

Zach Galifianakis: June 2013 vs. October 2014

The wolfpack just got a little smaller — and that's because Alan's half his size!

Zach Galifianakis, who played the insane, yet lovable character in The Hangover franchise, looked noticeably slimmer at the NYC premiere of his movie, Birdman, on Oct. 11, 2014.

The 46-year-old showed off his weight loss in a blue-striped gray suit.

Last year, the funnyman told Conan O'Brien he had stopped drinking and the weight just melted away. "I was having a lot of vodka with sausage," he joked. "Delicious, but bad for you."

Something tells us he'd lose an extra five pounds if he axed that facial fuzz!

Jerry Ferrara: June 2007 vs. June 2014

The 35-year-old actor looked incredible when he posed on the red carpet at the premiere of his film, Think Like a Man Too.

Best known for his role as lovable and trustworthy pal Turtle on the HBO series Entourage, Jerry says the reason for getting in shape wasn't for Hollywood — it was for himself.

"I didn't get in shape for anything having to do with the public, maybe there was a little bit of strategy behind it for transitioning outside of Entourage, but I can promise you the main goal was to get healthy," he told the Huffington Post. "It wasn't, 'I want to look a certain way.' It was more so feeling better. I didn't feel good. I smoked cigarettes. I was really overweight. I was always tired."

Jason Segel: June 2010 vs. July 2013

Jason revealed he slimmed down for his role in 2014's Sex Tape.

"I've just been living healthy, exercising, eating right — no more midnight pizzas," the 35-year-old How I Met Your Mother alum said at the time. "This time when I take my shirt off, I've made a promise to myself, it doesn't have to be funny."

The actor received a lot of backlash for Forgetting Sarah Marshall, where he was completely nude.

Perez Hilton: October 2007 vs. April 2012

The gossip blogger lost an incredible 70 pounds!

"At the beginning of 2008, I made a commitment to my health and I have stuck to it. Nearly four years later and I am in the best shape of my life!" he said in 2012. "I’ve lost more than 70 pounds and I’ve worked for it. I’ve done it the old-fashioned way, slow and steady, by eating healthily and exercising regularly. And I feel wonderful!"

Jason Sudeikis: May 2010 vs. March 2014

When you're engaged to one of the most beautiful women in the world, Olivia Wilde, and your career is hot in Hollywood, who can blame you for wanting to look and feel your best?

And the 40-year-old Saturday Night Live alum credits sex with Olivia for keeping him in shape!

"The truth is, I'm not getting up an hour earlier and walking on a treadmill. I have the greatest workout partner in the world," he said. "And you don't need a gym membership for that kind of workout."

Chris Pratt: August 2012 vs. July 2013

In the words of rapper Nelly, "It's getting hot in here!"

To prep for his role in Guardians of the Galaxy, the 36-year-old Parks and Recreation star transformed his beer belly into one heck of a six-pack.

After he Instagrammed the photo on the right last summer, all eyes were on the swoon-worthy star.

His advice for people wanting to get in shape? "I'll tell them, 'Hey, if you just bust your a– and get after it, all it takes is like six months really.' Six months flies by whether you're working out every day or whether you're not, so if you feel compelled to do something about it, take some action and get in shape, do it. You can do it. You could. You really could. You could do it in six months and all you have to do is just book a Marvel movie and have a deadline that's like, 'If you don't [lose weight] then you might get fired,' and then it's easy."

Drew Carey: June 2003 vs. April 2014

The 57-year-old Price is Right host's life changed in 2010 after he lost a jaw-dropping 80 pounds.

"It sucks being fat, you know," he said. "I was diabetic with Type-2 diabetes.”

Not anymore! He hit the gym and shed his diet of carbs, which led to him living a diabetic-free life.

"I have cheated a couple times, but basically no carbs, not even a cracker. No bread at all. No pizza, nothing. No corn, no beans, no starches of any kind. Egg whites in the morning or like, Greek yogurt, cut some fruit," he said about his diet.

As for working out, he says, "Lots of cardio. About 45 minutes of cardio, at least 45 minutes of cardio."