Chris Pratt had to drink two gallons of water a day during intense training for Star-Lord role

Chris Pratt had one particular 'nightmare' training habit he had to put up with when getting into shape to play Star-Lord for the Guardians of the Galaxy movies.

Before being cast as the spacefaring Marvel superhero, people knew Pratt as the cheerful but somewhat schlubby Andy Dwyer in Parks and Recreation.

However, when he landed the leading role in Guardians of the Galaxy he had to get into shape, and not just any shape but movie star action hero shape.

You've probably heard how stars like Hugh Jackman and Henry Cavill went through punishing regimes to play muscular protagonists who get shirtless on screen, and for the final touch before filming to be days of dehydration to tighten the skin.

However, in Pratt's case his personal nightmare during his exercise regime was over-hydration, as Marvel's nutritionist had him ditch the beer and replace it with a daily dose of about two gallons of water.

CHRIS DELMAS/AFP via Getty Images

Pratt shed about 60 pounds in six months to get into shape as Star-Lord which is quite incredible when you learn he was also on a diet of around 4,000 calories per day.

The actor said at the time that drinking so much water meant he was 'peeing all day long, every day' and said 'that part was a nightmare' when getting in shape for his role.

According to Vanity Fair, Pratt was first dismissed as 'totally wrong' for the leading part in Guardians of the Galaxy after he'd first auditioned to be Captain America, a part taken by Chris Evans.

Pratt did manage to get a screen test for Star-Lord and Guardians of the Galaxy director James Gunn said 'he's the guy' about 10 seconds into that, landing him the role.

Having put on weight to appear more 'schlubby' for Parks and Recreation, the onus was then on Pratt to hit the gym and get the kind of body that takes months of hard work, strict diet and apparently two gallons of water a day to achieve.

YouTube/Parks and Recreation

When he returned to Parks and Recreation, his body transformation was explained as his character having given up beer for one month.

While Pratt made quite the change for his Marvel movies, he's by no means the actor who made the most dramatic shift.

Vincent D'Onofrio has the record for the actor who gained the most weight for a role, piling on the pounds to play Private Pyle in Stanley Kubrick's Full Metal Jacket.

He had to gain 70 pounds for the part, and it took him nine months to shed the weight.

On the other end of things, Tim Realbuto shed 154lbs to appear in the movie Bobcat Moretti where his character is an obese MS patient who takes up boxing, meaning he had to lose the weight after shooting some scenes.