what words can i write about health and fitness?I really need help ASAP cause I need to hand it in tomorrow.

That's an enormous topic. People have written BOOKS about different parts of this topic.

http://www.google.com/search?q=health+and+fitness&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

Wander through those search results and see what you find. You can get different search results by changing the search words.