Orthorexia nervosa: A term designating a disorder in which there is an unhealthy obsession with healthy eating, an extreme dedication to extreme diets that can starve the body of basic nutrition. The emphasis (or overemphasis) is on the quality, not the quantity, of food in the diet. Orthorexia nervosa has not been recognized as an accepted medical entity.
The term was proposed in 1996 by the American physician Steven Bratman. Meant to parallel "anorexia nervosa." From the Greek "ortho-" (right and correct) + "-exia" (appetite) = right appetite.