If he has type 1 diabetes, diet and exercise won't do jack for him.
I have that very same disease and am hesitant to tell people for fear of being judged that I have it due to lifestyle choices. Nothing could be further from the truth. After all, I am 6' tall, 160 lbs, not an ounce of fat on me, and I work for UPS. It has been proven exhaustedly that insulin is the only option for people with diabetes 1. If I could change my lifestyle to get rid of my diabetes, I sure would. But how? I already eat healthy, exercise plenty, and don't drink alcohol...