Good question.  I think that there should be one time a day, or a sweet only as a reward for him doing something special.  Also, be aware of what you cook and the products you use.  Try not to make too many oily, pizza sort of meals for dinner.  Also, you can be aware of the amout that you put on his plate.  He is only six.  You can maybe give him a little less to eat... a 6-year-old doesn't need that much food to be satisfied.  Also, it is a good idea to give me an opportunity to run and play.  I'm not sure what activities he does, but he should have active things in his schedule several times per-week.  It is very healthy for both the mind and spirit.  Good luck!  I hope this helps.