Imagine having a job that demanded you gain weight by eating anything and everything.

Sounds great right? Wrong.

Several actors have revealed the extreme diets they adopted to pack on the pounds for movie roles and most of them did not enjoy the experience:

MATTHEW McCONAUGHEY

The Oscar winner gained 20kg to play modern day prospector Kenny Wells in the upcoming movie, Gold.

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And his three kids took great delight in their dad's method to pack on the pounds.

"I was an all star in my family, nicknamed Captain Fun during that time because I [said] yes to pizza night, every night and it was cheeseburgers and beer," McConaughey said.

Gold will be released in February next year.

JARED LETO

It's not known how much weight exactly Leto gained to play John Lennon's assassin in the 2007 movie Chapter 27 but it was a lot.

So how did he do it?

"(I did it) by eating everything you think you're not supposed to: pizza, pasta, ice-cream," he said according to Contact Music.

"But my little trick was I would take pints of chocolate Haagen Dazs [ice cream] and put them in the microwave and drink them. The sick thing is I would actually pour olive oil and soy sauce into the mixture as well to get me bloated even more."

The actor told MTV that doctors told him to stop the weight gain as it was getting too dangerous.

"It was doctors telling me I needed to stop, that I was going to kill myself, my cholesterol shooting up to 300 something points - which is bad," he said.

"They wanted to put me on Lipitor and all kinds of medication...Food is the strongest medication we take every day. What I was doing was poisoning myself with some really severe methods. It was a fascinating, but devastating experience."

Jared Leto in a scene from the movie, Chapter 27.
Jared Leto in a scene from the movie, Chapter 27.

RYAN GOSLING

The Canadian star put on 27kg to play Jack Salmon in the 2009 movie, The Lovely Bones.

Gosling achieved that by melting Haagen Dazs ice cream and drinking it whenever he was thirsty.

Unfortunately though Gosling didn't check with director Peter Jackson before gaining the weight and he was replaced by Mark Wahlberg before filming began.

"We had a different idea of how the character should look," Gosling said to the Hollywood Reporter.

"We didn't talk very much during the pre production process, which was the problem. It was a huge movie, and there's so many things to deal with, and he couldn't deal with the actors individually. I just showed up on set, and I had gotten it wrong.

"Then I was fat and unemployed."

GEORGE CLOONEY

The silver fox had to gain 13kg in a month to play Robert Barnes in Syriana and Clooney said packing on so much weight so quickly is "not nearly as fun as it sounds".

"My job was just to eat as fast as I could, as much as I could," he said to The Tech.

"But mostly you just ate until you wanted to throw up, and made sure you didn't throw up. So that was my job for a month, was eating."

George Clooney in a scene from the film, Syriana. Photo / News Corp Australia
George Clooney in a scene from the film, Syriana. Photo / News Corp Australia

COLIN FARRELL

The Irish actor also adopted the melted ice cream method to pack on almost 20kg for his 2015 movie, The Lobster.

"I would put [the ice cream] in the microwave to melt and drink it," he told The Hollywood Reporter.

"Two cheeseburgers, fries and Coca-Colas, and two slices of chocolate cake at 10am is not that fun - and I love cheese­burgers."

Colin Farrell in a scene from the film, The Lobster.
Colin Farrell in a scene from the film, The Lobster.

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MATT DAMON

Most of the stars who had to gain serious weight for roles often say that it wasn't a very enjoyable experience.

But Matt Damon disagrees.

He packed on almost 15kg to star in the 2009 movie The Informant

"It was very, very easy to gain the weight," Damon said to The Daily Mail.

"It was very, very fun, probably the funnest time I had working, because I didn't have to go to the gym after work and I just ate everything I could see.

"I definitely got doughy. I started eating like crazy and drinking dark beer. Between meals on set, I'd eat a No. 1 Value Meal at McDonald's and then Doritos on top of it. It was absolute heaven."

Matt Damon in a scene from the film, The Informant.
Matt Damon in a scene from the film, The Informant.