The electronic music duo - comprised of Karl Hyde, 62, and Rick Smith, 60 - avoid the pitfalls of "overeating" and getting into unhealthy habits on the road by reminding themselves that "the camera adds 10 pounds".
Speaking to Q magazine, Karl said: "It's just living life moderately and realising that one day you're going to look really s**t on camera if you eat too much cake."
Rick added: "The hardest thing is the two worlds that we spend a lot of time in, one is a studio world and looking after yourself when you're working in a cave when the pressure is on isn't very healthy.
"And the other is being on tour, which can go to real extremes. "You can be overeating because the food in front of you is so interesting or there's never the food you need to eat when you want it because you've only had three hours' sleep and you haven't got time for breakfast."
Underworld have had their music featured in many movies over the years, including the tracks 'Dark & Long (Dark Train)' and 'Born Slippy.NUXX' from 1996's 'Trainspotting', and they also later teamed up with the movie's helmer Danny Boyle in directing the music for the opening ceremony of the 2012 Olympic Games.
The pair admitted it's difficult to name famous scores which they they'd like to have worked on.
Karl explained: "The thing is with a film and a score when it's blown you away the last thing you'd want to do is change it."
Rick agreed and referred to the times he's been asked to remix music he believes is already great.
He added: "Like 'Taxi Driver', how are you going to try and change that?
"I've been asked to remix amazing records at various points and I'm not really interested. When it's that amazing... no, no, no."