Either don't game every day or setup like an hour a day for exercise or some physical activity such as hiking or biking. Also watch what you eat or drink while gaming, a lot of sugary drinks can lead to diabetes which can lead to other health issues later on. Also staring at a screen for extended periods of time can be bad for your eyes. And while this is rare some have actually developed blood clots which can actually result in a heart attack. It's important to take breaks when you can.
When I was heavily playing MMO's (Blade & Soul, City of Heroes) the sessions were like 8 hours long but taking a 10-15 min break (to stretch, walk around, not look at the screen) every 1.5-2 hours helped a lot. If your going to snack eat something healthy or portion out something that may not be so healthy so your not going to overindulge. I do wish however I was better with eating better because when I was younger as in the 10 years I was playing COH I gained nearly 120 LBS which eventually led to type 2* diabetes which sucks. Had to be on a ton of medications including insulin (needle sticks) but over the past few years I'd made healthier decisions and now only take 2 meds (down from 12) and lost about 80 LBS.
Stuff you can do while gaming is...
-Play while on a exercise bike (use a controller as it would be easier then K/M) or exercise ball.
-Squats (again easier with controller but 90% sure Warframe supports controller).
-Push-ups or something else while you wait for a team to form or raid. Any kind of exercise when there's some gameplay downtime would help immensely.
Hope this helps!