Worried about a friend? (losing weight)?

If you take a look at this 'healthy weight chart', you'll see that your friend is on the very verge of being healthy. But this chart is just a guideline, and can differ depending on your body type. However, it seems that your friend may be dangerously close to developing an eating disorder (if she hasn't already). Visible ribs are not normal. It also isn't normal that she weighs herself constantly or survives on one meal a day. She isn't giving her body the nutrients it needs. Talk to her. If you can, encourage her to go to the doctor, or confide in her parents.