Objective: In Anorexia Nervosa (AN) distorted body image beliefs range from overvalued ideas to delusions, significantly influencing illness trajectory. However, these phenomena remain underexplored, particularly in other Feeding and Eating Disorders (FED). This systematic review and meta-analysis investigates the prevalence and clinical significance of delusional-like beliefs related to body image and eating concerns in FED.
Method: Following PRISMA guidelines, PubMed, Web of Science, and the Cochrane Library were searched for quantitative studies (1960-January 2025) investigating delusional-like beliefs in FED. Random-intercept logistic regression and network meta-analysis were conducted. Study quality was evaluated using the dedicated tool from the National Heart, Lung, and Blood Institute. The review was registered on PROSPERO (CRD42024553915).
Results: Sixteen studies met inclusion criteria from 4122 initial records (1711 participants), mostly involving individuals with AN. Most samples originated from Western countries, introducing location bias. Delusionality was assessed using tools such as the Brown Assessment of Beliefs Scale and Nepean Belief Scale. Meta-analytical estimates indicated overvalued ideas in 32.5 % and delusional-like beliefs in 23.6 % of AN patients, with no significant heterogeneity. Greater belief rigidity correlated with poorer insight and possibly more severe eating-disorder psychopathology. Network meta-analyses showed significantly lower delusionality in AN patients compared to Body Dysmorphic Disorder, with no significant differences from other controls. Study quality was low, limiting robustness.
Conclusion: Delusional-like beliefs are present in a substantial subset of individuals with AN, which underscores their clinical significance, potential transdiagnostic relevance, and implications for tailored therapeutic strategies. Further research is needed on other FED and longitudinal outcomes.

