Adaptation and Validation of the Gluten-Free Perceived Nutrition Environment Measures Survey (NEMS-P-GF) and Its Association with Gluten-Free Diet Adherence Among Adults with Celiac Disease in Chile

Background/Objectives: Strict adherence to a gluten-free diet (GFD) is the only effective treatment for celiac disease (CeD) but remains challenging due to structural and environmental barriers. Evidence on these determinants in Latin America is scarce. This study aimed to adapt and validate the Gluten-Free Perceived Nutrition Environment Measures Survey (NEMS-P-GF) for adults with CeD in Chile and examine its association with GFD adherence. Methods: A cross-sectional online survey (October 2023–January 2024) included adults (≥18 years) with biopsy- or serology-confirmed CeD (n = 233). The questionnaire collected sociodemographic and clinical data, assessed adherence using the Celiac Dietary Adherence Test (CDAT; good < 13, poor ≥ 13), and measured perceptions of home and supply food environments via the adapted NEMS-P-GF. Construct validity was tested using exploratory factor analysis and reliability with Cronbach’s α and McDonald’s ω. Associations with adherence were analyzed using Mann–Whitney U. Results: NEMS-P-GF domains showed adequate validity (KMO 0.71–0.81; Bartlett’s p < 0.001) and acceptable-to-excellent reliability (α/ω = 0.70–0.90). Participants with good vs. poor adherence perceived more supportive environments, particularly at home (median 4.79 vs. 1.29; p < 0.01) and globally (1.72 vs. −7.25; p < 0.01). Supply environments were perceived as less supportive due to limited availability and high prices (median −3.68 and −7.78), with smaller differences between adherence groups (p = 0.018). Conclusions: Supportive home environments were strongly associated with better GFD adherence, while supply environments remained broadly restrictive, showing modest but significant differences between adherence groups. The NEMS-P-GF demonstrated preliminary evidence of good psychometric properties and offers a valid, context-sensitive tool to assess GF food environments and inform public health strategies for CeD populations.