Eat and walk
It goes without saying how important breakfast and lunch are for our health. But, you have to go further: always have a light snack at hand, in fact, at your desk. Having a healthy snack (such as fruits, vegetables, or nuts) between your regular meals prevents you from starving, so you don't overeat. In addition to that, it gives you more opportunities to get in all of your nutritional needs.
And why not take this lunch break to get up and stretch your legs? So, grab your snack and go for a walk while enjoying it.