Diabetes or Aids. Why are some diabetics so, so thin?

My friend who was always in great shape back in college has diabetes. I had not seen him in 8 years and now he looks like a skeleton. How come some diabetics are so thin? I know people with diabetes and they don't look old and thin like him. He looks like he will blow away. When I mentioned his weight he acts as if he is not thin. I hate the way he looks, its so hard to be near him. I hate that I feel this way. Please show me a site where diabetics get really thin.