I need to get my friends off my back. Any ideas?

I'm on a diet. I'll admit its pretty strict, I don't eat much and when i do I have laxatives, I take dietry supplements, do a fair bit of excersize. My friends don't know some of that but they do know that i am on a strict diet only because i told them I was on one. Did I make a mistake by telling them? They are worried about me now and no matter how many times that I tell them I am fine they won't believe me untill I stop what I am doing which is easier said then done. How can I get them to stop worrying about me and get them off my back?