Working out? P90x? other alternatives?

I know a couple of people that have done the P90X, and have made small gians, but once they stopped, what they lost all came back. I am 39 years old, and have been a Type 1 diabetic since I was 15. At 18 I decided it was time to put on some weight ( I was really skinny) and the working out would be good for my health. Since then I have worked 3-4 times a week faithfully, for only an hour eachtime. I have been told I am in very good shape, but I owe all that to just doing it weekly. Your body will let you know what works and what does not, just pay close attention to how it feels. I still lift heavy, but I find now I respect how I do the exercises more, and make sure I am careful. I am no longer out to impress anyone. All exercise is good if you can get into a routine and keep up with it as well. Going to the gym is my addiction. Hope you can find a plan that works for you. Have you tried supplements such as l-glutuamine before?