To our knowledge, this is the first study to screen for ON using the DOS in a large and diverse population of patients with RMDs. Among individuals living with RMDs, screening positive for ON was most commonly observed in those with FMS and SLE, particularly among women and those with longer disease duration. Conversely, individuals with IIM showed a reduced risk of ON, indicating a decreased prevalence of concerns pertaining to orthorexic behaviors.

There is a prevailing notion that autoimmunity is linked to eating disorders via shared biological pathways through the psychoneuroimmunological axis and underlying inflammatory processes [37, 38]. The presence of pain, physical dysfunction, and an impaired quality of life (QoL) has been identified as a contributing factor to the development of depression and social isolation [39]. Anxiety disorders have also been observed to be prevalent within this population [39], and consist of risk factors for an obsessive focus on healthy eating [40]. Moreover, the findings of this study indicated that while most patients were free of ON-risk, they adhered to stringent dietary regimens and prioritized health over the enjoyment of food, suggesting a tendency towards disordered thinking in relation to food.

FMS involves chronic musculoskeletal pain, joint and muscle stiffness, fatigue, and a range of psychological and cognitive symptoms, including mood disorders, cognitive dysfunction, anxiety, and depression [19, 41]. It affects women disproportionately [42], with growing evidence indicating that they are more likely to adhere to restrictive diets, avoid foods such as cereals, alcohol, and soft drinks, and prefer herbal products instead [43]. Concerns regarding body weight and physical appearance are also commonly reported, as are emotional eating and eating-related concerns [44, 45]. Furthermore, serum levels of brain-derived neurotrophic factor (BDNF) are negatively associated with hunger, thereby suggesting a potential correlation between eating patterns and dopaminergic activity in individuals with FMS [44]. In the present study, patients with FMS were found to be at higher risk for ON, which prompts further investigation into whether dietary rigidity in FMS represents a coping mechanism, a response to misinformation about “anti-inflammatory” diets, or an expression of underlying anxiety and perfectionism.

SLE primarily affects women and is associated with a broad range of clinical manifestations, such as renal, pulmonary and cardiac involvement [46]. Neuropsychiatric manifestations are observed in over half of patients with SLE [47], including symptoms such as psychosis, depression, anxiety disorders, and cognitive dysfunction [48, 49]. Although ON has not yet been systematically studied in this population, many individuals with SLE report favoring plant-based diets, reducing the consumption of animal products and processed foods, making dietary changes aimed at alleviating symptoms [50], and adhering to disordered eating [30]. Our findings indicate that patients with SLE exhibited greater DOS scores, suggesting an increased predisposition to orthorexic behaviors. These overall tendencies may reflect health-focused dietary control, but also raise important questions regarding the potential emergence of orthorexic behaviors in the context of chronic autoimmune disease.

Eating disorders appear relatively common among individuals with SLE, and recent genome-wide association studies (GWAS) have identified a shared genetic locus between autoimmune disorders and AN, underscoring the role of genetic predisposition in this comorbidity [30, 51]. Several case reports and case series have documented the occurrence of AN in patients with SLE [51] and juvenile-onset SLE (jSLE) [30], with the majority of reported cases involving girls and young women. Beyond genetics, chronic inflammation emerges as another shared pathway, as both conditions are characterized by elevated levels of pro-inflammatory cytokines [37, 38]. Furthermore, brain-reactive autoantibodies identified in SLE have been shown to disrupt neurotransmitter systems involved in appetite regulation [51]. Within this framework, AN in the setting of SLE could plausibly be regarded as a neuropsychiatric manifestation of SLE, driven primarily by immune dysregulation and inflammatory mechanisms rather than being solely a side effect of treatment [30, 51]. In the context of a post-SLE diagnosis, the clinical manifestations of autoimmune disease, in conjunction with treatment-related changes such as weight gain induced by corticosteroids and altered appearance, may have the potential to act as triggers for psychosocial stressors [31, 51].

Inflammatory myopathies consist of heterogeneous diseases that affect primarily the skeletal muscle, along with other organs, and lead to myalgia and weakness [52]. These manifestations often contribute to a reduced QoL in patients with IIM, who frequently report low energy levels and increased social isolation [53]. In addition to these challenges, physical impairments and elevated rates of depression appear to play a significant role in further lowering QoL scores [53]. A particularly impactful factor influencing QoL is dysphagia, which is highly prevalent among patients with IIM [52, 54]. This swallowing disorder can cause various difficulties, potentially leading to serious complications such as aspiration pneumonia and unintended weight loss [52]. Consequently, individuals encountering such challenges may struggle to maintain a balanced diet and may not prioritize strict ‘clean’ eating, instead focusing on foods that are less likely to worsen swallowing issues. This may be particularly relevant when interpreting the absence of increased orthorexic risk observed among patients with IIM.

Altered body perception has been reported more frequently among women [31], and ON appears to follow the same trend [55]. In the context of RMDs, women were found to be at-risk for ON [32], a finding that was also supported by the present study. This pattern may be partly explained by changes in body image [31], which can stem from RMD-related alterations in physical appearance, disease flares, and greater functional limitations [56]. These factors may contribute to heightened body awareness and more rigid dietary attitudes. Moreover, the fear of deterioration and relapse is a characteristic feature of chronic diseases [15]. In this context, many patients develop a strong desire to prevent or manage their condition by adopting a healthy, whole-food diet [57, 58], which may be relevant to the orthorexic patterns exhibited by individuals with a prolonged disease course.

Nevertheless, while studies in the general population report a high prevalence of orthorexic behaviors —sometimes affecting more than half of individuals [59]– such tendencies appear to be far less common among patients with RMDs. This contrasts sharply with other chronic conditions, such as diabetes mellitus [11], inflammatory bowel disease [14], and celiac disease [12], as well as with lifestyle groups that follow highly restrictive eating patterns, such as vegetarianism [60]. In these conditions, strict dietary modifications are often perceived as central to symptom control and disease management, resulting in a strong emphasis on nutrition and a willingness to adopt highly restrictive diets. In RMDs, however, disease management primarily relies on pharmacological interventions, with dietary modification being considered as complementary, rather than essential. Nutritional advice in these disorders is typically supportive and advisory, rather than prescriptive or mandatory [61], leaving less room for the development of rigid and perfectionistic attitudes toward food. Furthermore, the burden of chronic pain, fatigue, physical disability and reduced QoL that frequently accompanies RMDs [39] may limit both the motivation and the practical ability to adhere to highly structured and restrictive dietary routines.

However, orthorexic tendencies warrant careful consideration, specifically within the setting of RMDs. Research has demonstrated that chronic illness can precipitate cognitive and psychological vulnerability [62]. While patients with RMDs didn’t screen positive for ON at elevated rates, certain diagnoses showed a higher frequency of orthorexic behaviors. This highlights the need for a cautious and balanced approach to food and dietary patterns, especially when these are promoted as complementary strategies in disease management. Several dietary interventions—such as the Autoimmune Protocol (AIP) diet—have been suggested to help alleviate symptoms of autoimmune diseases [58]. However, these approaches, which run in parallel to ON, often involve the elimination of multiple food groups and, if undertaken without the guidance of a qualified nutrition professional might lead to nutrient deficiencies [58]. As a consequence, they may contribute to the development of disordered eating behaviors, an unhealthy relationship with food [58], and nutritional deficits, or over-restriction that may worsen disease outcomes [27, 28]. Nevertheless, the repercussions of ON impact extend beyond the physical domain, encompassing the social and psychological domains; they reverberate beyond physical health, eroding psychological well-being, straining social relationships, and ultimately diminishing overall QoL [63]. Furthermore, such tendencies have the potential to diminish adherence to treatment regimens, favoring ‘natural’ dietary methods over pharmacotherapy and consequently resulting in an unfavorable disease progression. Given the significance of various metabolic conditions such as malnutrition [64], sarcopenia [65], and rheumatoid cachexia [66] in the context of RMDs, the emergence of ON may further exacerbate these implications. Thus, dietary recommendations in patients with RMDs should be personalized, evidence-based, and accompanied by appropriate clinical and psychological support.

This study is not without limitations. This is a cross-sectional analysis, in essence; therefore, it is not possible to draw causal relationships. Moreover, the incorporation of a control group would have been advantageous in enhancing the quality of the study and reinforcing the findings. ON screening was conducted using the DOS [33, 34], as no diagnostic tools have been validated and universally accepted for ON assessment. Moreover, the grouping of certain diseases into more general categories is conducive to the prevention of loss of statistical power; however, it is important to note that this may result in a limitation of valuable insights. Also, actual dietary practices were not assessed, which could have provided a more comprehensive background of the recorded orthorexic tendencies. Similarly, variables such as depression, anxiety, and body image were beyond the scope of the present study and thus, not recorded, although they might have offered additional context. Linear regression analyses were performed instead of ordinal regression models, due to the disproportionate distribution of participants in the first DOS category. This may have affected the ability to capture the full ordinal nature of the outcome variable.