What does the ORTO-15 measure? Assessing the construct validity of a common orthorexia nervosa questionnaire in a meat avoiding sample.

Orthorexia nervosa (ON) is a proposed diagnostic category that captures a pathological need to eat healthfully. The ORTO-15 is a self-report measure ostensibly designed to assess ON, but its suitability for capturing symptoms of pathology has been questioned. Vegans differ from omnivores in their focus on health and present with similar or lowered endorsement of eating behaviors symptoms, making them an ideal group to assess the construct validity of the ORTO-15. We tested the hypothesis that the ORTO-15 captures normative, rather than pathological, health focus. In total, 106 omnivores, 34 meat reducers, 50 lacto-ovo-vegetarians, and 191 vegans completed the ORTO-15 to quantify the presence and severity of ON and the Eating Disorder Examination Questionnaire (EDE-Q) as an established measure of eating pathology. More than 75% of respondents met criteria for a diagnosis of ON per established ORTO-15 cutoffs. Respondents above the 2.50 EDEQ cutoff (suggesting the likely presence of an eating disorder) did not differ in ORTO-15 scores from those scoring below the cutoff. There was a univariate main effect of meat avoidance type on the EDE-Q global scale (p < .01), with vegans endorsing fewer symptoms on the EDE-Q than semi-vegetarians (post-hoc p < .05). Vegans were more likely to meet the clinical ON cutoff of 40 on the ORTO-15 compared to omnivores (omnibus p < .01; post-hoc p = .01). Based on the ORTO-15, vegans' scores should be indicative of pathological eating behavior, but EDE-Q scores instead indicate the lowest levels in this group. The ORTO-15 is able to differentiate between types of meat avoiders, but given the difference in health focus between groups, the scale may be tapping into a construct other than pathological eating beliefs and behaviors.