Shared Fryers May Not Always Be as Risky for Gluten Cross-Contact in Celiac Disease as Dietary Guidance Suggests

Background: Shared fryers are commonly perceived as a high-risk source of gluten cross-contact for individuals with celiac disease (CeD), leading to widespread avoidance of foods such as French fries and tortilla chips. However, limited real-world data exist evaluating gluten concentrations in foods prepared in shared fryers under routine food service conditions. Because long-term health outcomes in celiac disease depend on minimizing cumulative dietary gluten exposure and intestinal injury is dose-dependent, characterizing gluten contamination from common dining practices has important implications for nutritional management and disease counseling. Objective: The aim of this study was to quantify gluten concentrations in naturally gluten-free (GF) foods prepared in shared fryers across U.S. food service establishments and to evaluate how fryer management practices, restaurant type, and geographic distribution influence gluten content. Methods: This cross-sectional observational study analyzed gluten concentrations in 98 samples of French fries (n = 55) and tortilla chips (n = 43) collected from fast food, fast casual, casual dining, and fine dining establishments, cafés, and other food service settings across multiple U.S. states. All samples were naturally GF prior to frying and prepared in fryers shared with gluten-containing foods. Gluten concentrations were measured using an enzyme-linked immunosorbent assay (ELISA). Recorded variables included sample type, restaurant type, state location, and fryer oil change frequency (daily, weekly, or unknown). In accordance with the U.S. Food and Drug Administration (FDA) GF labeling standard, foods containing <20 ppm gluten were considered GF, while values ≥20 ppm were classified as exceeding the GF threshold. Values <5 ppm were considered below the assay’s limit of quantification (LOQ). Results: Of the 98 samples analyzed, six (6.1%) exceeded the FDA GF threshold of 20 ppm. The majority of samples (84/98, 85.7%) measured below the assay’s lower LOQ (<5 ppm gluten). All 43 tortilla chip samples tested <5 ppm. Among samples from fast food establishments, 9/12 (75.0%) measured <5 ppm, 2/12 (16.7%) measured 5–20 ppm, and 1/12 (8.3%) exceeded 20 ppm. Among samples from fast casual establishments, 13/15 (86.7%) measured <5 ppm, 1/15 (6.7%) measured 5–20 ppm, and 1/15 (6.7%) exceeded 20 ppm. Greater variability was observed in casual dining establishments, including samples exceeding 20 ppm. All samples collected from establishments reporting daily oil changes measured <20 ppm, while samples from establishments reporting weekly oil changes demonstrated higher and more variable gluten concentrations, including values greater than 20 ppm. Conclusions: In this multi-site observational study, shared fryers were not uniformly associated with meaningful gluten cross-contact. Gluten concentrations varied by food service context and fryer management practices, with consistently low or below-LOQ gluten levels observed in establishments reporting daily fryer oil replacement, and greater variability observed in settings with less frequent oil changes. These results indicate that shared fryers are not inherently high-risk sources of gluten cross-contact and highlight daily fryer oil replacement as a key operational factor significantly associated with lower measured gluten levels. These findings have direct nutritional implications. Estimating gluten concentrations in shared-fryer environments allows for more accurate assessment of potential daily gluten intake, which is the key determinant of mucosal healing, serologic normalization, and long-term nutritional and health outcomes in individuals with celiac disease.