Low Body Weight and Bone Loss - Being thin puts a women at increased risk of developing osteoporosis (a condition which, believe it or not, often leads to death in older women). Amenorrhea virtually guarantees it. Those with anorexia can lose as much as 2% to 6% of their bone mass each year they have AN.
Impact of Low Body Weight on Brain Function - Underweight individuals with AN had significant deficits in brain grey matter volume compared to healthy controls. These deficits in grey matter volume improved with short-term weight restoration, but did not fully normalize during the year-long study. (Usually clients to not realize they are cognitively impaired until they get better and look back at their symptoms.)