When I was growing up I had no idea what was healthy or not. I didn't until I moved out and started taking care of myself. As long as your not projecting guilt on the kid I think it's great. Knowledge is a powerful tool and the younger you get it the better off you'll be in this world. Many adults live with bad habits they learned as children and just don't know how to change. What your doing is called "Guidance" and it's great that your taking an intrest in his future wellbeing. Teach him as much as you can while he's still young enough to actualy listen to you. (When they become a teenager all they will hear you say is Blah Blah Blah I'm an idiot, don't listen to me Blah Blah)
Why all this discussion about food? Just serve him good healthy meals, no junk, and no excess sweets. The emphasis you are placing on his diet verbally may have the opposite effect by making him think about food all the time. Meal-time should be a happy occasion, not a lecture. Children learn by example. If you eat properly, and only good food is available, he will follow your lead. You suggest that your husband is overweight - this is not a good example. He should start with himself.