I think the article means that 18-25% is ideal . . . I think "healthy" is not necessarily the right term. Although I've heard reports that anything less than 15% can cause health problems.
Women don't usually cease menstruation until they get around 10%, though. Anything near that can cause problems, because we need a decent amount of body fat to live healthily -- but most women aren't going to significantly harm their bodies until they hit about that "about 10 percent" figure and stop menstruating.
I'm trying to find an article that backs this up, but so far, none of the articles on the subject mention a specific body fat percentage that is dangerous. I just remember that, while running cross-country in high school, our coach gave us tons of information and articles to read on this subject because runners are really susceptible to it, and ten percent is the figure that stands out for me.
