First, if I had a kid that was overweight I would not give him dairy. I would cut way back on that. I have some other ideas, let us know what the test results show and I can give you some more thoughts then.
You may want to look at this site to give you some ideas. I am not suggesting that you go completely raw vegan. You may just want to up the amount of raw food you give your son. It will make a difference.