In this study we assessed two important research issues regarding orthorexia nervosa in ED patients. First, we assessed the possibility to identify latent classes in our ED sample; on the basis of the statistical criteria, we were able to distinguish two different latent classes of ED patients. The main differences between latent classes concerned fat anxiety, weight perception and orthorexic behaviours. In the group which reported a lower level of eating pathology, orthorexic behaviours were more frequent; on the contrary, in the group reporting higher levels of eating pathology, orthorexic behaviours were less frequent. These findings are consistent with those by McInerney-Ernst , who found that in a group of American female students, orthorexic symptoms were related to a lower level of eating pathology, while less orthorexic traits were found in students with symptoms strongly associated with severe EDs. Eating-related disturbances have been suggested as risk factors for orthorexia , and the reverse is also possible. Indeed, as underscored by Mac Evilly , orthorexia may be a risk factor predicting a future ED. Orthorexic eating habits could become more and more restrictive and compulsive, actually resembling ED symptoms . Moreover, studying the relationship between orthorexia and EDs, Segura-Garcia and coworkers  found that orthorexia may precede the onset of a full-syndrome ED, or represent its evolution during remission and recovery. Similarly, according to Cartwright , orthorexia could precede or follow anorexia, and orthorexic behaviour could be a socially-approved way to express anorexic symptoms. What described by Segura-Garcia  and Cartwright  is likely to impact on patients’ score on questionnaires assessing ED symptomatology and orthorexia. Specifically, we may suppose that patients with an acute, full-syndrome ED may score higher on the first and lower on the latter; on the contrary, patients in an early or late stage of their ED may report less ED symptoms and display more orthorexic features. Anyway, these issues are still controversial; the current literature is not univocal and it is not clear whether orthorexia is a new ED, a different psychiatric disorder, a disorder at all, or a variant of the existing EDs.
As far as our results are concerned, we were surprised finding a group of clinically-diagnosed ED patients without the typical ED symptoms as assessed with the EAT. Nonetheless, some hypotheses can be suggested. First, as described in the results section and in Table 1, it should be noted that in our sample most patients suffered from bulimia nervosa, with a relatively brief duration of illness, and these clinical features may reflect themselves in the questionnaire scores. We should also consider that the EAT is a screening, self-report instrument, with all the limitations that this entails, including the impossibility to exclude dissimulative behavior and hiding the symptoms on behalf of patients. ED patients could show this attitude towards the psychological test in the attempt to adapt themselves to the existing social norms, to hide the real disorders, or perhaps, according to the belief that doing so would shorten their treatment.
We can suggest another hypothesis, considering that in our sample ED patients scoring low on the EAT scored high on the ORTO-15, and that we found a negative correlation between orthorexia and health orientation. It is possible that some patients score low on the EAT but high on the ORTO-15 because they “mistake” their symptoms for healthy behaviors or try to convince themselves (or others) that their behaviors are healthy, and classify them according to this distorted assumption. The result is that ED symptoms may be denied or hidden under a healthy facade. Actually, patients in the first class we identified (low scores on the EAT, high scores on the ORTO-15) evaluated their health higher than patients in the second class.
Anyway from a clinical standpoint, whatever the relationship between orthorexia and EDs, the overlaps between orthorexia and EDs, as well as their differences, should be considered when developing a therapeutic program tailored to the patients’ specific needs. For instance, as already described, orthorexic individuals and ED patients focus on quality/purity of food and quantity of food, respectively. The distorted cognitions underlying an ED are different from those typical of orthorexia nervosa, and should be differently addressed.
The second aim of the study was the identification of predictors of orthorexia nervosa in the ED patients group, which was assessed using the SEM methodology. In SEM we are testing complex regression models, therefore the stronger the coefficient is, the more the independent variable is predicted by the dependent one. All of significant predictors were negatively explaining orthorexic behaviours. This supports the findings described above, from the LCA, i.e., that orthorexic behaviours in the clinical group we assessed are more frequent in those patients with a less severe ED pathology, less weight concern and appearance orientation. The strongest (negative) predictors of orthorexic behaviours were ED pathology and weight concern, with both predictors highly correlated. Anyway these results should be interpreted with caution, considering the small sample size and the fact that ED pathology and weight concern share issues such as fat anxiety, dieting, eating restraint or food and weight perception. As suggested by the LCA, only behaviours related to ED pathology are negative predictors of orthorexia nervosa.
On the other hand, unexpectedly, health orientation, which measures the extent of investment in healthy lifestyle and appearance orientation, which measures the extent of investment in own appearance emerged as a negative predictors of orthorexia. This may be surprising considering that orthorexia has been defined by Bratman & Knight  as “a fixation on eating healthy food” in order to avoid ill health and disease. An hypothesis is that a discrepancy might exist between healthy lifestyle as conceived by orthorexic individuals and what is a real and actual healthy lifestyle. As discussed above, since we included patients with a clinical diagnosis of ED, maybe in our sample the surface is orthorexia, but the underlying reason for this behavior is an eating disordered attitude, which has little or nothing to do with avoidance of ill health and disease. The concept of healthism as described by Haman and coworkers  may be helpful clarifying this point. Healthism refers to a social construction of health, a “new health consciousness” assuming that health can be achieved easily through individual discipline and moral conduct, focusing on body size and shape [26, 27]. This point of view may not coincide with actual health. Indeed, healthism practices can lead to an improvement of one’s habits as well as to unhealthy behaviors and ideas about body shape, diet and physical exercise [25, 27]. The criteria for what is considered healthy are likely to be highly personal . In the healthism model, the individual is blamed for health problems, and social pressures exist towards constrained behaviors of self-surveillance, which may eventually be transformed into unhealthy, harmful and even destructive behaviors [29, 30]. The risk is that detrimental behaviors become normalized, and that ED patients replace in a more socially acceptable way the typical ED symptoms with orthorexic behaviours.
Moreover, based on the literature [6, 31–33], we should consider that, although it seems that orthorexic behaviours have more parallel with anorexia nervosa than with bulimia nervosa, it is noteworthy that the similarities between anorexia nervosa and orthorexia nervosa (e.g., intense anxiety regarding certain foods and their avoidance, need for control, ego-syntonic nature ) have not been empirically established . In our study most patients were diagnosed with bulimia nervosa and classified as normal weight. Like bulimia nervosa, orthorexia is a disorder rooted in food intake. Patients with unhealthy fixation on healthy eating are restricting whole food groups. However, dieting in bulimia nervosa is associated with increased food restriction . Unlike bulimia nervosa, orthorexia nervosa is about control of food intake.