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Introduction Non-coeliac gluten sensitivity (NCGS) remains a controversial clinical entity at the intersection between disorders of gut-brain interaction (DGBI) and avoidant/restrictive food intake disorder (ARFID) symptoms. However, current prevalence data are limited by methodological heterogeneity, and the extent of the overlap with DGBI and ARFID remains poorly defined. We aimed to determine the prevalence of self-reported NCGS using a uniform methodology and to characterise its association with DGBI and ARFID in the adult general population.Methods We conducted a population-based internet survey with pre-defined demographic quotas across the USA and UK in 2023. Participants completed the Rome IV diagnostic questionnaire, the Nine-Item ARFID screen, and validated instruments for psychological distress, somatisation, and quality of life. Multivariable logistic regression was used to assess the associations between NCGS and DGBI/ARFID, adjusting for demographic factors and mood disorders.Results A total of 4,002 participants (50% female; median age 46 years [IQR 33 – 66]) were included in the analyses. The prevalence of self-reported NCGS was 14.2% (95% CI, 13.1 – 15.3), with comparable rates between the USA (13.5%; 95% CI, 12.0 – 15.1) and UK (14.8%; 95% CI, 13.3 – 16.5). Compared with participants without gluten sensitivity, those with NCGS reported significantly more non-gluten food intolerances (median 3 vs 0, p<0.001), were more likely to have at least one DGBI (58.7% vs 40.3%; aOR 1.80; 95% CI, 1.49 – 2.18) and to screen positive for ARFID symptoms (34.8% vs 24.3%; aOR 1.46; 95% CI, 1.20 – 1.77). Among individuals with NCGS, 69.4% (95 CI, 65.4 – 73.1) had concomitant DGBI and/or ARFID, with nearly one-quarter (24.0%; 95% CI, 20.6 – 27.8) meeting criteria for all three conditions. This three-way overlap represented a distinct high-severity phenotype characterised by marked psychological distress, somatic symptom reporting, increased healthcare utilisation, and reduced quality of life (all p<0.001)Conclusions NCGS is reported by approximately 1 in 7 adults in the USA and UK. Our findings suggest that NCGS may represent a broader syndrome of food-related symptom attribution rather than gluten-specific pathology.