In a 1997 article in the magazine Yoga Journal, the American physician Steven Bratman coined the term "orthorexia nervosa" from the Greek ορθο- (ortho, "right" or "correct"), and όρεξις (orexis, "appetite"), literally meaning 'correct appetite', but in practice meaning 'correct diet'. The term is modeled on anorexia, literally meaning "without appetite", as used in the definition of the condition anorexia nervosa. (In both terms, "nervosa" indicates an unhealthy psychological state.) Bratman described orthorexia as an unhealthy fixation with what the individual considers to be healthy eating. Beliefs about what constitutes healthy eating commonly originate in one or another dietary theory such as raw foods veganism or macrobiotics, but are then taken to extremes, leading to disordered eating patterns and psychological and/or physical impairment. Bratman based this proposed condition on his personal experiences in the 1970s, as well as behaviors he observed among his patients in the 1990s. In 2000, Bratman, with David Knight, authored the book Health Food Junkies, which further expanded on the subject.
Following the publication of the book, in 2004 a team of Italian researchers from La Sapienza University of Rome, published the first empirical study attempting to develop a tool to measure the prevalence of orthorexia, known as the ORTO-15.
In 2015, responding to news articles in which the term orthorexia is applied to people who merely follow a non-mainstream theory of healthy eating, Bratman specified the following: "A theory may be conventional or unconventional, extreme or lax, sensible or totally wacky, but, regardless of the details, followers of the theory do not necessarily have orthorexia. They are simply adherents of a dietary theory. The term 'orthorexia' only applies when an eating disorder develops around that theory." Bratman elsewhere clarifies that with a few exceptions, most common theories of healthy eating are followed safely by the majority of their adherents; however, "for some people, going down the path of a restrictive diet in search of health may escalate into dietary perfectionism." 
Karin Kratina, PhD, writing for the National Eating Disorders Association, summarizes this process as follows: "Eventually food choices become so restrictive, in both variety and calories, that health suffers – an ironic twist for a person so completely dedicated to healthy eating."
Although orthorexia is not recognized as a mental disorder by the American Psychiatric Association, and it is not listed in the DSM-5, as of January 2016, four case reports and more than 40 other articles on the subject have been published in a variety of peer-reviewed journals internationally. According to a study published in 2011, two-thirds of a sample of 111 Dutch-speaking eating disorder specialists felt they had observed the syndrome in their clinical practice.
According to the Macmillan English Dictionary, the word is entering the English lexicon.