Renee Zellweger totally transformed her body for both 'Bridget Jones' movies. She piled on roughly 28 pounds for each film.
For the first movie, Renee simply stuffed herself with as many donuts and cheese pizzas as she could. For the second, a nutritionist helped her gain weight with a more controlled high calorie diet.
Renee revealed that it sounded "like heaven" to be able to "indulge all your fantasies about over-eating. Fantasies about non-stop chocolate consumption or your fantasies about ordering the pizza and the spaghetti and the garlic bread." However, in reality, "After a week your glucose levels are going crazy. You're up and down and all over the place. It doesn't feel good, and no one wants to hear that, but it's the truth."
Regarding losing the weight Renee said, "It was horrible," and that "the first lap around the track I felt like I had a toddler on my back."
Click through for more startling examples of stars who gained or lost massive amounts of weight for movies.
Remember, these are extreme cases -- Don't try these dangerous diets at home!
Rapper 50 Cent lost so much weight in preparation for filming 'All Things Fall Apart' that he ended up looking like a different person altogether. He lost 54 pounds to play a football player with cancer, losing muscle weight, and dropping down to 160 pounds from his regular 214.
50 Cent's weight loss process involved a liquid diet, and walking on the treadmill for up to three hours per day. It was not easy. According to 50 Cent, "I was starving."
Matthew McConaughey became shockingly skinny to play Ron Woodroof, a Texan electrician who has HIV/AIDS, in the movie 'The Dallas Buyers Club.' He lost 47 pounds for the part.
That weight loss took its toll, with Matthew saying he had "Probably got 35 percent less energy."
What worked for him:
"I'm doing cardio but I'll tell you what, the more I've learned is – and I think it comes with age too – is it's 90 percent diet. It's 90 percent amount and then what you're eating because right now I'm not losing any more weight if I burn 1,500 calories, two hours of cardio in an afternoon, or if I don't. It doesn't matter. It's a matter of how much I eat or how little I eat."
His post-shoot meal plans:
"I will have some 70 percent beef, 30 percent fat ground beef, maybe a half pound cheeseburger with another three types of cheese. I'll prepare it all and I'll make sure that it takes three hours just to prepare. I'm going to have buns with butter on both sides, toasted and grilled. I'm going to melt the cheese on the top bun, Hellmann's Real Mayonnaise. I want kosher dill pickles sliced nice and thin, diced white onions, slightly grilled until they get almost hard, and some thin jalapeno slices. And then I'm just going to sit back and let the [expletive] just drop on the ground."
Jared Leto is no stranger to extreme body transformations for movie roles. And like his 'The Dallas Buyers Club' costar, Matthew McConaughey, he lost a drastic amount of weight for the movie. Jared plays the part of Rayon, a transsexual woman who has HIV. His weight dropped to around 116 pounds after his 30 pound weight loss.
Jared's weight loss technique? "I just basically didn't eat. I ate very little."
The results were shocking. He says, "It's not a great thing to see. If you run into people or see family who don't know what you're doing, they think that you're sick."
An already thin Anne Hathaway lost an extra 25 pounds to play Fantine in the movie 'Les Miserables.'
Anne started out by going on a strict cleanse, during which she lost 10 pounds. Then she lost an extra 15 pounds on a near starvation diet, eating a meager two thin squares of dried oatmeal paste each day.
Anne says, "I had to be obsessive about it -- the idea was to look near death. Looking back on the whole experience -- and I don’t judge it in any way -- it was definitely a little nuts. It was definitely a break with reality, but I think that’s who Fantine is anyway."
To play Brett in the November 2013 comedy film 'Delivery Man,' actor Chris Pratt gained 60 pounds "the old fashioned way: eating and drinking my face off."
But his next role, as Star-Lord in 'Guardians of the Galaxy,' scheduled for an August 2014 release, calls for a completely different look.
It seems he's making great progress, judging by his ripped abs in the photo he posted to his Instagram account in July 2013. His secret? "Six months no beer."
Glamorous actress Charlize Theron gained 30 pounds to transform herself into serial killer Aileen Wuornos for the movie 'Monster.' She also had blotchy makeup applied, and wore crooked prosthetic teeth.
Charlize's weight gain sounds relatively easy:
"I first began stuffing myself with Krispy Kreme donuts but after a while I got sick of them. I love potato chips, so that was a good thing for me. I’m a salty girl so I had my secret stash with me of potato chips at all times. Basically you eat all the junk that you really want to eat for the first few months but after a while that get's boring. But I never got tired of potato chips. I could live off potato chips!"
As for trimming back down again, Charlize admits, "It’s tough. It’s not as much fun as actually gaining it. but I had to go straight into another film so I had no choice but to train hard and go on a strict diet."
After being signed to play the lead in the movie 'The Lovely Bones,' Ryan Gosling set himself the task of bulking up for the role.
Ryan gained 60 pounds by "melting Haagen Dazs and drinking it when I was thirsty. I really believed in it, I was excited about it and I showed up and they said, 'You look terrible.'"
As a result, he was fired by director Peter Jackson, and replaced by Mark Wahlberg. Ryan says, "I was 150 pounds when he hired me and I showed up on set 210 pounds. We had a different idea of how the character should look."
Gaining weight for the movie 'Million Dollar Baby' took a lot of dedication and hard work from Hilary Swank. According to her, "The producers asked me to gain 10 pounds of muscle. I gained 19 pounds of muscle. I started at 110 and went to 129."
How she did it:
Eating 210 grams of protein per day.
Eating every hour and a half.
Drinking egg whites and flax oil.
Getting nine hours of sleep per night.
On top of that, she had to learn how to box. Hilary says, "Boxing is the most intense workout you can ever experience...The only way I can explain it is if you were to take a jump rope and go as fast as you could for three minutes while someone's punching you in the stomach."
In order to fully immerse himself in the movie 'Cast Away' Tom Hanks put his body through some serious weight changes.
Starting from his normal weight of between 185 and 195 pounds, Tom chunked up to 230 pounds to play the out of shape Fed Ex worker Chuck Noland. Part way through filming, production stopped to allow him to lose weight and look like a realistic desert island castaway. By the end of the movie his weight had plummeted to 172 pounds.
According to Tom, "I just stopped working out and ate anything whenever I felt like it, pretty much. It affects your sleep, it affects your legs, never mind your cholesterol. I mean, I was fat. There's some shots on the island where that belly is just sticking out there."