You probably can't. The people who "never have time" or "simply can't [fill in the blank]" may have excuses, but they may have reasons, too, that we just can't see.
What you CAN do is create an opportunity to make a different choice.
- Managers: Try setting different expectations. Could you be rewarding star employees even when they compromise their wellbeing by overworking?
- Coworkers: Be a pal. How recently have you said, "You work so hard. What would make it possible for you to take a break?" Just one invitation from someone else to take a break together might be the excuse they need to start a new routine.
- Box Lunch Lifestyle Enthusiasts: You are proof that it IS possible in your workplace to take a break, eat something better, and feel better overall. You are the real deal. People will notice, and some will follow your lead.
The thing about giving someone an opportunity to make a different choice is that you're not asking them to say they're wrong. (People HATE wrong.) But they might say, "Huh. I didn't realize that. Okay. I'll give it a try."