Rapper 50 Cent got all serious about his acting in 2011, when he lost FOUR STONE for his role in Things Fall Apart.
The star went on a strict liquid diet to play the role of an American football player suffering from cancer.
And here's Fiddy in his normal, buffed-up state.
Anne Hathaway lost 25 pounds to platy Fantine in Les Miserables.
The actress claimed she stopped eating for 13 days during shooting... Oh and had her hair hacked off with a knife.
Seems to be paying off though - so far Anne's already nabbed a Golden Globe and SAG Award and is nominated for an Oscar.
Hi Anne's lovely long hair and curves pre Miserables!
Ahh... look how Bootylicious Beyonce is here!
But to play Deena Jones at age 16 and 36, two weeks apart, Beyonce dropped 20 pounds by doing the Master Cleanse Diet, where you drink six to 12 glasses a day of a special mix of lemon juice, maple syrup and cayenne pepper.
Charlize Theron gained 30 pounds and underwent daily prosthetics to play real-life serial killer Aileen Wuornos in Monster... and bagged an Oscar in the process.
Here's modelesque Charlize as we're more used to seeing her.
Christian Bale (actual Batman) lost about 63 pounds for his role as an insomniac in The Machinist, apparently starving himself for four months living on a cup of coffee, an apple or a tin of tuna EVERY DAY.
And here's the Batman we know and love.
Oh hai George Clooney looking slimline on the red carpet!
Oh, um, hi George Clooney in 2005, with a big old beard and 35 pounds heavier in Syriana...
Jared Leto showed off his dramatic weight-loss for his role in the Dallas Buyers Club as a transsexual with AIDS at the end of last year. It's not the first time he's lost weight for a role - his weight also plummeted when he starred in Requiem for a Dream in 2000.
Jared also gained 60 pounds to play Mark David Chapman in Chapter 27 in 2007.
We're not sure what his actual normal figure is like any more.
Matt Damon (aka People magazine's Sexiest Man Alive 2007) piled on the pounds in 2009 for his role in The Informant!
Matt - slimmer and in a suit. Nice.
We've been FASCINATED in Matthew McConaughey's weight loss for the Dallas Buyers Club (which Jared Leto also lost his weight for).
But we're also pretty FASCINATED by Matthew in last year's Magic Mike.
Here's Natalie Portman, looking petite as ever earlier this year.
But in 2010 Natalie Portman became the ultimate Tiny Dancer when she lost 20 pounds from her already tiny frame to play the lead in Black Swan.
She won an Oscar though... anyone starting to notice a pattern?
Renee Zellweger's not known for looking her curves...
But when Renee took on the task of playing Bridget Jones she had to put on 30 pounds. Then she lost it. And had to gain it again for the sequel.
Tom Hardy totally transformed his body in 2008 to play Charles Bronson in... um, Bronson.
He said: "To “become” Charlie Bronson I had to quickly put a lot of weight quickly on my forearms, chest and neck.
"By the time I’d finished, my legs looked like those of a stork in comparison to the top half of my body."
Ahhh there's the Tom we know and love. Non-stork legs and all.
Aww, look, there's Will Smith!
But to play Muhammad Ali, Smith turned his 185 pound fram into 220 pounds of muscle with six-hour-a-day workouts!
Oh, and um, he got an Oscar nomination.