Jeffrey Dean Morgan Lost 45 Pounds by Eating Only One Can of Tuna a Day — Plus 13 More On-Screen Transformations!

Mark Wahlberg in The Gambler

The father-of-four dropped a staggering 60 pounds to portray gambler Jim Bennett in the fictional film The Gambler.

“I went from 197 to — the lightest I’d ever been in a movie was in Boogie Nights, I was 138 — so I wanted to beat that,” he said. “I beat it by a pound, so 137. I was losing weight while we were shooting the movie, too, so continuity kind of went out of the window.”

Tilda Swinton in ‘Trainwreck’

While filming in Brooklyn, N.Y., the 54-year-old actress was seen wearing a brunette wig, heavy makeup and some tanning cream.

What we're used to seeing is a bare-faced actress with short bleach blonde hair.

Jared Leto in ‘Chapter 27’

Skinny Jared Leto was once 67 pounds heavier! In fact, it was only about eight years ago for his film Chapter 27 where he played John Lennon's assassin.

"[I did it by] eating everything you think you're not supposed to—pizza, pasta, ice cream," Leto said about his high-fat diet, "but my little trick was I would take pints of chocolate Häagen Dazs and put them in the microwave and drink them."

Renée Zellweger in ‘Bridget Jones’s Diary’

Who could forget Renée Zellweger in Bridget Jones's Diary?!

To play the star of the film, the 47-year-old actress gained a reported 30 pounds, which she obtained by going on a 4,000 calorie-a-day diet eating high-calorie, high-fat foods, such as donuts and pizza.

Nowadays, the actress is sporting a slimmer figure and was even criticized last year for appearing to have an eating disorder. She, of course, slammed those rumors saying they were "unfair and disappointing."

Jake Gyllenhaal in ‘Nightcrawler’

In his film, Nightcrawler, Jake not only grew his hair much longer, but lost a considerable amount of weight. He plays a a driven freelance crime journalist who has a very American Psycho look about him, don't you agree?

"(I lost) probably a little over 20 pounds or so. I'm playing a character that is hungry literally and figuratively," the actor said of altering his body for the role.

50 Cent in ‘All Things Fall Apart’

Now this is 50 Cent like we've never seen him before! For the film All Things Fall Apart, the rapper went from a reported 214 pounds to 160 in just nine weeks with a liquid diet and working out three hours a day.

"This time it was a lot tougher for me," 50 Cent aka Curtis Jackson said about his role at the time. "I had to discipline myself not…to actually have myself be in the physical state to convey the energy I felt. It's a passion project for me."

Elle Fanning in "Three Generations"

When we saw Elle Fanning on the New York set of her new film, "Three Generations," we had to do a serious double take.

We'd say the 18-year-old has successfully transformed for her role as a transgender teen who's transitioning from female to male.

Naomi Grossman in "American Horror Story: Freak Show"

Pepper may give you nightmares after you watch American Horror Story: Freak Show (and that's the point), but underneath all of that TV makeup is a dream girl!

Naomi Grossman, who portrays the spooky character, recently revealed, "I’ve never been told I was so pretty until I played the ugliest person on TV. But now I have a twin! So now maybe he’s ugliest?"

Charlize Theron in ‘Monster’

The transformation from beautiful starlet to deranged killer was not an easy task! However, Charlize Theron pulled it off for the 2003 crime film.

The 41-year-old actress is seen in the film sans eyebrows, a fuller figure (30 pounds heavier), with dentures, contact lenses and sun-damaged, aged skin.

Zoë Kravitz in ‘The Road Within’

To play an anorexic and bulimic character in The Road Within, Zoë had to drop 20 pounds from her already small frame. So how did she accomplish the risky transformation?

“I did a cleanse,” she revealed. “I tried to do it the healthiest way as possible, even though it’s not healthy to do.”

While most associate cleansing with juices and clean eating, Lenny Kravitz and Lisa Bonet’s famous daughter went a slightly different route.

“I ended up drinking clay,” the 26-year-old confessed. “Because it cleans out your body and fills you up. I was eating like a Mason jar of pureed vegetables and running.”

Hugh Jackman in ‘Blackbeard’

The Jack of All Trades tweeted this shot of his jaw-dropping transformation.

Robert Downey Jr. in ‘Tropic Thunder’

Robert Downey Jr.'s transformation to play Kirk Lazarus was quite extreme! For the comedy film, the Iron Man star put on a chocolate complexion and kinky black hair. In the film, he plays a white actor who dons blackface to play a role as a soldier that was originally written for a black man.

"If I didn't feel it was morally sound," Downey said, "or that it would be easily misinterpreted that I'm just C. Thomas Howell in (Soul Man), I would've stayed home."

Jeffrey Dean Morgan in Texas Rising

The Grey's Anatomy alum lost 45 pounds for his role in the History Channel series Texas Rising, dropping from 175 to 130. But the father-of-two admits the way in which he did it was awful!

"I ate a can of tuna fish a day," he told Today. "I did it in the most unhealthy way possible…I didn't consult with a doctor or anything."

Rooney Mara in ‘The Girl With The Dragon Tattoo’

Rooney Mara had one of the most dramatic transformations ever to play the star of The Girl With the Dragon Tattoo, Lisbeth Salander. Rooney was in character for about a year and has gotten some tattoos and piercings (with the rest of them being removable) – including nipple rings! She even shaved parts of her head to play the world class computer hacker.

"Yes, it was really helpful. I wanted to do everything; the piercings, everything. At that point, I was already in the character and ready to be even more so," the 31-year-old actress said about changing for her role. "For me, my long blonde hair was weighing me down. I was really happy to get rid of it and just get on with things."

Michelle Rodriguez

For the movie Tomboy, the Latina actress flattened her breasts and wore an "itchy" beard for her role as a male assassin.

"I never felt more like a woman than when I played a man," she said of the experience.