The aim of this article is to present the up-to-date diagnostic tools of orthorexia and markers of its prevalence on the basis of the available literature. The authors searched PubMedCentral (PMC) and Google Scholar with the search entry of "orthorexia", "orthorexia nervosa", and "orthorexicbehaviours". We describe the tools of evaluation of orthorexicbehaviour (i.e., orthorexia self-test-BOT, the ORTO-15 questionnaire, Eating Habits Questionnaire-EHQ, Düsseldorf Orthorexia Scale-DOS, Teruel Orthorexia Scale-TOS, Barcelona Orthorexia Scale-BOS, and Orthorexia Nervosa Inventory-ONI), and offer a review of the studies on orthorexia nervosa. We conclude that there are no reliable data regarding the prevalence of orthorexia nervosa. The available studies point to significant differences in the prevalence depending on the value of cut-off points and tools used. The prevalence varies across countries and across populations, ranging from 6.9% in the Italian population to 88.7% in the group of Brazilian students of dieting. Thus, it indicates that some groups seem to be susceptible to the risk of ON more than others. It is a challenge to determine the prevalence of orthorexia, and any obtained results should be treated with caution. Consequently, we claim that the use of the ORTO-15 questionnaire to diagnose orthorexia is questionable due to a high percentage of falsely positive results.
Keywords: ORTHO-15; eating disorders; orthorexia nervosa; prevalence; tools.