Being Underweight Puts People at Highest Risk of Dying - Underweight adults (BMI under 18.5 or less) have a 1.8 times higher risk of dying than those with a "normal" BMI of 18.5 to 24.9. This is HIGHER than for those who are "obese" and even for the severely "obese."

Moderate Thinness Can Be Unhealthy - People who are overweight have a lower risk of death than those of normal weight. The researchers -- statisticians and epidemiologists from the National Cancer Institute and the Centers for Disease Control and Prevention -- also found that increased risk of death from obesity was seen for the most part in the extremely obese, a group constituting only 8 percent of Americans. And being very thin, even though the thinness was longstanding and unlikely to stem from disease, caused a slight increase in the risk of death. This study is considered by many independent scientists to be the most rigorous yet on the effects of weight.

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.)