I'm one of those people. I have a very thin bone structure, which helps with the weight, and a screwy metabolism. For some people, it just kinda happens. My mom recently got the book Younger (Thinner) You by Eric R. Braverman, M.D. It's not a diet but a way of changing the way you eat based on brain chemistry. You cut out all "white" food (white bread, potatoes, pastas and such), most sweeteners, and add lots of spices and foods that deal with the brain chemicals that you lack (there's a survey type thing that helps you figure out what you need more of). Her doctor recommended it to her so we're all going to try it. I'm definitely not looking to loose any weight but I know I need to start taking better care of myself. We'll see how this works.