As evidenced by the following:

Compulsive behavior and/or mental preoccupation regarding affirmative and restrictive dietary practices believed by the individual to promote optimum health. (Footnotes to this criteria add: Dietary practices may include use of concentrated "food supplements." Exercise performance and/or fit body image may be regarded as an aspect or indicator of health.) Violation of self-imposed dietary rules causes exaggerated fear of disease, sense of personal impurity and/or negative physical sensations, accompanied by anxiety and shame. Dietary restrictions escalate over time, and may come to include elimination of entire food groups and involve progressively more frequent and/or severe "cleanses" (partial fasts) regarded as purifying or detoxifying. This escalation commonly leads to weight loss, but the desire to lose weight is absent, hidden or subordinated to ideation about healthy food.Criterion B. The compulsive behavior and mental preoccupation becomes clinically impairing by any of the following:

Malnutrition, severe weight loss or other medical complications from restricted diet
Intrapersonal distress or impairment of social, academic or vocational functioning secondary to beliefs or behaviors about healthy diet
Positive body image, self-worth, identity and/or satisfaction excessively dependent on compliance with self-defined "healthy" eating behavior.A diagnostic questionnaire has been developed for orthorexia sufferers, similar to questionnaires for other eating disorders, named the ORTO-15. However, Dunn and Bratman critique this survey tool as lacking appropriate internal and external validation. Epidemiology
Results across scientific findings have yet to find a definitive conclusion to support whether nutrition students and professionals are at higher risk than other population subgroups, due to differing results in the research literature.
Orthorexia nervosa  (also known as orthorexia) (ON) is a proposed eating disorder characterized by an excessive preoccupation with eating healthy food. The term was introduced in 1997 by American physician Steven Bratman, M.D. He suggested that some peoples dietary restrictions intended to promote health may paradoxically lead to unhealthy consequences, such as social isolation, anxiety, loss of ability to eat in a natural, intuitive manner, reduced interest in the full range of other healthy human activities, and, in rare cases, severe malnutrition or even death.In 2009, Ursula Philpot, chair of the British Dietetic Association and senior lecturer at Leeds Metropolitan University, described people with orthorexia nervosa as being "solely concerned with the quality of the food they put in their bodies, refining and restricting their diets according to their personal understanding of which foods are truly pure." This differs from other eating disorders, such as anorexia nervosa and bulimia nervosa, where those affected focus on the quantity of food eaten.Orthorexia nervosa also differs from anorexia nervosa in that it does not disproportionally affect one gender. Studies have found that orthorexia nervosa is equally found in both men and women with no significant gender differences at all. Furthermore, research has found significant positive correlations between ON and both narcissism and perfectionism, but no significant correlation between ON and self esteem. This shows that high-ON individuals likely take pride over their healthy eating habits over others and that is the driving force behind their orthorexia as opposed to body image like anorexia.