Kudrow told the Popcrushed podcast she suffered from body dysmorphia, adding that she wrongly felt like a 'stick' like her sister and father.
"I didn't see it. I had no waist. I didn't see it at all. I thought I was just really skinny and I could just do whatever," she explained.
"And I would look at pictures and be like, 'Wow, pictures really distort reality'. It wasn't until Friends that I realised that I don't really look like I thought I looked. That's what was so jarring and that's when I was like, 'I've gotta actually lose weight? I have to diet? Shoot'."
Asked whether the media had impacted her change in perception, Lisa put it down to 'just seeing herself on the show' and simply seeing how the female trio looked in clothes.
Kudrow said she asked Aniston, who played Rachel Green and Cox, who starred as Monica Gellar to accompany her to various fittings to offer their wisdom. At that point she realised it 'wasn't just about tailoring'.
She added: "I'm not trying to say I was overweight either. I was not. I just had no idea of the actual shape of my body."
Kudrow went on to reveal that she finally began to accept her body upon reaching her 40s, telling herself: "Do what you need to do to be healthy but this is your body and it's OK."
It comes after Aniston recently revealed that the girls ate the same salad every day for 10 years while filming.