As i understand it, essentially people are kind of stuck with the body type they have in regard to where they tand to gain and lose fat.
You can use the body fat calculator on this site to check to make sure you are not too low in body fat (http://www.zonediet.com/Tools/Calcu...ult.aspx).
The ideal for the average female is around 20%. If you're below 18%, double or triple the number of fat blocks you add to meals until you gain back to at least 18%. At that point you'd go back to the usual amount of fat in your meal. In one of his books (I think it's in MASTERING THE ZONE), Barry Sears explains how to use dietary fat in this manner to maintain ideal body fat.