Kumail Nanjiani suffered "some body dysmorphia" after he started to bulk up.
The 42-year-old actor embarked on an intense fitness regime for a new movie role - but the decision ultimately led him to experience some body image issues.
He said: "I don't want to discount people who genuinely have debilitating body issues. I don't have that. But I did start getting some body dysmorphia.
"I'd look in the mirror and I'd see my abs - and when I looked again, they would fade. I would just see the flaws."
Kumail ultimately decided to post an image of his newly-muscular physique on social media.
And the comedy star thinks his much-discussed Instagram photograph helped him to overcome his body image concerns.
He told the April issue of Men's Health magazine: "When I saw that reaction was when I was like, 'Okay, I clearly don't see what's actually there.'
"It's something I'm trying to be aware of and be better at, because that's not a good way to be. You want to be easy on yourself."
Kumail embarked on his fitness drive in preparation for the new Marvel movie 'Eternals'.
And the actor - who previously starred in HBO's comedy series 'Silicon Valley' - admitted he didn't "want to be just part of the Marvel movie - I wanted to be a Marvel superhero".
Kumail's energy-sapping workout regime was unlike anything he'd ever previously done.
He said: "I realised, if this is what working out is, I've never really worked out a moment in my life ... I had to change my relationship to pain.
"You're so designed to avoid it, but in that situation you really have to be okay with it. You have to want it. It's almost trying to rewire your brain."