Hi Kathy. Like you too, way back in my 20's I was super thin. I also ate very small portions and probably not the best of foods. I also was an over exerciser, trying to keep that thin model shape. The key is, I SHOULD HAVE done things in moderation. Anything in extreme is bad.
I wished I had known these things back than, that I know know.
I would have changed a great deal in my lifestyle.