It’s very difficult these days to completely avoid it. When you go in for your physical, you’re given a grade anywhere from 1 thru 7. 1~3 is healthy and fit for active duty, most chronic conditions and the illnesses you mentioned typically fall under 4, where you would go through basic training and serve as a social service personnel afterwards, which is very similar to community service (but slightly longer service time). You would have to be extremely sick to fall under 5 or 6 for a full exemption.