Conceptualisation of restrictive repetitive behaviours across autism and orthorexia nervosa

Orthorexia Nervosa (ON) is widely regarded as an emerging eating disorder although it is not currently recognised as a formal diagnosis. It is characterised by a strict adherence to “pure” eating which becomes excessive and can lead to nutritional deficiencies, psychological distress, and impaired daily functioning. Restrictive eating behaviour in ON shows overlap with Restricted Repetitive Behaviours (RRBs) observed in autism. However, the conceptual relationship between ON and autism remains underexplored. This perspective article synthesises existing literature to explore potential overlapping and diverging mechanisms of RRBs across ON and autism. Intolerance for Uncertainty is highlighted as a possible shared mechanism that may contribute to RRBs observed in both ON and autism, whereas Cognitive Inflexibility and Perfectionism may mechanistically differentiate the conditions. We consider that autistic RRBs reflect neurodevelopmental divergence, whereas orthorexic RRBs may be influenced by evaluative belief-centred cognitions. We propose a conceptual model outlining how cognitive, affective and functional factors may interact to produce and maintain RRBs. Clarifying these distinctions is important in supporting clinicians to appropriately consider the drivers and mechanisms underlying RRBs across ON and autism, therefore supporting accurate diagnosis, formulation and treatment.