The 35-year-old actor, who stars in the highly anticipated Jurassic World, opened up in the July issue of Men's Health U.K. about his physical and emotional issues in 2013 when he was almost 300 lbs. while working on Parks and Recreation.
"I was impotent, fatigued, emotionally depressed. I had real health issues that were affecting me in a major way," Pratt told the magazine. "It's bad for your heart, your skin, your system, your spirit."
The actor – who has a 2-year-old son, Jack, with his wife, Anna Faris – went on to explain that he thought his popularity in Hollywood was due to his overweight appearance.
"I saw myself in an episode [of Parks and Rec] and in the matter of two moments very close together, I thought, 'Oh my God, I'm getting fat.' "
"And then almost immediately I did something else and I thought, 'Holy crap, I've never seen myself funnier.' And I put the two together," he explained.
Pratt decided he wanted to shape up when he signed on for Zero Dark Thirty.
"I'd gone back and forth, lost weight for Moneyball, got fat again, then trimmed down for Zero Dark Thirty, then gained it all back again for Andy," he recalled.
"That's when I saw Zero Dark Thirty and right after walking out I was like, 'I'm going to get in shape and I'm never going to be fat again.' "
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Now, Pratt is smoldering on magazine covers (Hello, Entertainment Weekly wet-shirt moment) and adventuring around the world to promote the new dinosaur adventure flick.
And he's been documenting his journey along the way.
"I want to make a heartfelt apology for whatever it is I end up accidentally saying during the forthcoming #JurassicWorld press tour," the actor joked on Facebook recently.