emaciation -
The state of being emaciated or reduced to excessive leanness; an excessively lean condition.
Wikipedia
Emaciation occurs when an organism loses substantial amounts of much needed fat and often muscle tissue, making that organism look extremely thin. The cause of emaciation is a lack of nutrients, starvation, or disease. Many women (and some men) have targeted the emaciation look, and such is the result of eating disorders such as anorexia nervosa and bulimia.
