Teaching is a profession that can invite bad health because of the high stress and weird hours that are often involved with it. It's hard enough to teach well when you are in good health. Being at your best as a teacher when you haven't taken care of yourself is nearly impossible.
Classroom management is much harder to deal with when you are already stressed out and in a bad mood before you even begin.
Don't let your teaching career ruin your health. It's a great thing to do, but it's not worth killing yourself over.
What you eat, how much you sleep, and the amount of exercise you get are all important factors for health. Don't make excuses about why you can't take care of yourself. Sometimes you just have to make yourself behave in these areas. Not only will it make you feel better, it will also help your performance in the classroom.
Don't be the sleep deprived, sugared up, out of shape slob who suffers through the day and takes out stress on your classes. Your students deserve better.