Orthorexia, or orthorexia nervosa in full, is closely related to the disorder anorexia nervosa. With anorexia, the sufferer has an unhealthy obsession to lose weight while with orthorexia, the subject has an unhealthy obsession with "healthy eating". The subject may avoid certain types of food, such as those containing fats, preservatives or animal products. As a result, the sufferer may become as hazardously thin as those suffering from anorexia.

The condition was identified by Dr. Steven Bratman, a Colorado specialist. Bratman coined the term for the condition in 1997 from the Greek orthos, "correct or right", and orexis for "appetite".

Though the word is entering the English lexicon, it is not yet a recognized medical condition.