Orthorexia is derived from the Greek words "orthos" meaning correct and "orexis" meaning appetite. It refers to an obsession with healthy food and proper nutrition. Initially, it may stem from a desire to improve one's health, but for some individuals, it escalates into an obsession with healthy eating and avoiding foods they deem "unhealthy" or not "clean" enough. Although orthorexia is not currently classified in the DSM-5 or ICD-11, there are provisional criteria and several studies highlighting its serious symptoms and consequences. This has led some experts to predict its eventual inclusion in diagnostic manuals. However, there is currently no consensus among experts on how to define orthorexia precisely. The lack of a clear definition and validated measures for orthorexia makes it challenging to establish its relationship with various factors such as biological, psychological, social, and behavioral aspects. Therefore, the objective of this research was to propose a biopsychosocial model of orthorexia in women, considering orthorexia as a risk factor in the development of eating disorder symptoms. To achieve this, we identified the most appropriate measure of orthorexia and differentiated it conceptually from diagnostically classified eating disorder symptoms and obsessive-compulsive behavior. The study involved 1337 women aged 18 to 21 from all counties of the Republic of Croatia in a cross-sectional survey conducted online. The participants completed various selfassessment measures related to orthorexia, eating disorder symptoms, and factors associated with biology, psychology, social interactions, and behavior, which could predispose individuals to orthorexia or eating disorders. The results demonstrated that the Teruel Orthorexia Scale and the Düsseldorf Orthorexia Scale exhibited a good fit to the data, confirmed the expected factor structures with high factor saturations of all items, and displayed high internal consistency reliabilities. Furthermore, both measures showed significant intercorrelation. However, the ORTO-R scale was deemed unsuitable for measuring orthorexia due to its poor fit to the expected factor structure, low factor saturations, low internal consistency reliability, and unexpectedly low correlations with the other two orthorexia measures. Among the TOS and DOS measures, the Teruel Orthorexia Scale was selected as the most suitable measure for this research due to its two-factor structure, differentiating between healthy orthorexia and pathological orthorexia, known as orthorexia nervosa. This distinction provides valuable insights into the relationship between orthorexia and other constructs, distinguishing between individuals displaying signs of healthy orthorexia (non-pathological concern for health and nutrition) and those exhibiting symptoms of orthorexia nervosa (pathological obsession with healthy food). Confirmatory factor analysis was conducted to test two bifactor models: one aimed at differentiating orthorexia from eating disorder symptoms and the other aimed at differentiating orthorexia from obsessive-compulsive behavior. The results indicated that orthorexia, eating disorder symptoms, and obsessive-compulsive behavior can be considered distinct constructs. They sufficiently measure different aspects and justify their separate assessment within the biopsychosocial model of orthorexia, as they independently contribute to the model and explain specific variations among the variables under investigation. Moreover, orthorexia showed a stronger similarity to eating disorder symptoms than to obsessive-compulsive behavior. Using structural equation modeling, two alternative models were tested, wherein orthorexia's position was altered. One model considered orthorexia, alongside biological, psychological, social, and behavioral factors, as a predictor of eating disorder symptoms. The other model positioned orthorexia as a mediator between these factors and eating disorder symptoms. The results demonstrated that only the model where orthorexia acted as a mediator showed a very good fit to the data. This finding suggests that orthorexia is not a direct part of the psychological factors that predict eating disorder symptoms, but rather plays a mediating role within the model. It implies a complex relationship among biopsychosocial factors, orthorexia, and eating disorder symptoms, involving both direct and indirect pathways. In the accepted biopsychosocial model, wherein orthorexia acts as a mediator, all tested factors explained 35% of the variance in healthy orthorexia and 53% of the variance in orthorexia nervosa. The entire biopsychosocial model of orthorexia, including all factors and orthorexia, accounted for 75% of the variance in preoccupation with thinness, 61% in preoccupation with food, 17% in bulimic behavior, and 56% in avoidance of specific foods. The model also revealed that certain biological, psychological, social, and behavioral factors significantly predicted orthorexia and eating disorder symptoms. These factors had direct effects and indirect effects on eating disorder symptoms through both healthy and pathological orthorexia. Additionally, it was found that healthy orthorexia predicted less pronounced eating disorder symptoms, while pathological orthorexia predicted more severe symptoms. Specifically, older age, a greater tendency to wash and mentally neutralize, a lesser tendency to hoard, higher levels of rigid perfectionism, a greater inclination to eat due to positive mood, internalization of muscularity, spending more time following healthy eating- related content on social networks, following a larger number of people on these platforms, and current and previous restrictive dieting were significant predictors of healthy orthorexia. On the other hand, a greater tendency to wash and have obsessions, a higher inclination to eat due to loneliness, perceiving current appearance as fatter and ideal appearance as thinner, internalization of thinness and muscularity, pressure from family and the media, spending more time following healthy eating-related content on social networks, and current and previous restrictive dieting were significant predictors of pathological orthorexia, orthorexia nervosa. Additionally, higher body mass index, a greater tendency to have obsessions, more pronounced rigid perfectionism, perceiving current appearance as fatter and ideal appearance as thinner, greater internalization of thinness, higher pressure from peers and the media, and current and previous restrictive dieting predicted a more pronounced preoccupation with thinness, a symptom of eating disorders. Older age, a lesser tendency to wash, a greater tendency to have obsessions, higher pressure from family, and current restrictive dieting predicted a greater preoccupation with food. Furthermore, greater self-critical perfectionism and an ideal appearance perceived as thinner predicted bulimic behavior, while current restrictive dieting predicted avoidance of specific foods. Furthermore, healthy orthorexia was found to significantly predict less preoccupation with thinness and food, less pronounced bulimic behavior, and more frequent avoidance of specific foods. Orthorexia nervosa, in contrast, predicted more severe symptoms across all eating disorder symptomps. The study also considered the indirect paths of biopsychosocial factors to eating disorder symptoms through healthy orthorexia and orthorexia nervosa. The findings revealed that older age, a greater tendency to wash, lesser self-critical perfectionism, a lesser inclination to eat due to positive mood, internalization of muscularity, spending more time following healthy eating-related content on social networks, following a larger number of people on these platforms, and current dieting predicted more pronounced signs of healthy orthorexia. In turn, healthy orthorexia predicted less severe symptoms of eating disorders and more frequent avoidance of specific foods. Conversely, a greater tendency to wash, more pronounced obsessions, a higher inclination to eat due to loneliness, perceiving current appearance as fatter and ideal appearance as thinner, greater internalization of thinness and muscularity, higher pressure from the media, spending more time following healthy eatingrelated content on social networks, and current dieting predicted more severe eating disorder symptoms through orthorexia nervosa. In conclusion, this research provided a comprehensive understanding of various biological, psychological, social, and behavioral factors as risk and protective factors in the development of orthorexia and eating disorder symptoms. It also shed light on the role of orthorexia as a risk factor for eating disorder symptoms in women aged 18 to 21. The study examined and compared three commonly used measures of orthorexia, identifying the most appropriate measure for assessing orthorexia and distinguishing it conceptually from eating disorders and obsessive-compulsive behavior. The findings highlighted the significance of healthy orthorexia as a non-pathological concern for one's health and nutrition, serving as a protective factor against eating disorder symptoms. Conversely, orthorexia nervosa, characterized by a pathological obsession with healthy food, was identified as a risk factor for eating disorder symptoms. These insights can assist in recognizing the symptoms of orthorexia and developing appropriate interventions and treatment plans for individuals with orthorexia. The study also provided clear guidelines for future research in this area.