Understanding cross-contamination in a gluten-free diet: A scoping review

Maintaining a gluten-free diet (GFD) requires avoiding gluten containing grains, and preventing cross-contact with gluten-containing foods. Concerns about cross-contaminations can restrict food choices and may lead to behaviors resembling disordered eating. While guidelines state that gluten cross-contamination should be avoided, previous reviews and meta-analyses focused on whether contamination occurs, rather than its extent. Understanding contamination levels is crucial for risk assessment, resulting in a balanced approach that supports GFD adherence without hypervigilance or maladaptive eating behaviors.

A scoping review methodology was conducted across databases including MEDLINE, EMBASE, Scopus and Web of Science databases. Studies with real-life gluten contamination data were included. The protocol was registered on the Open Science Framework (https://osf.io/nhq84) and follows PRISMA-ScR guidelines.

From 4044 screened studies, 59 met the inclusion criteria (1993-2024, 28 countries). The analysis identified 27,806 food samples, predominantly analyzed by sandwich ELISA R5. Of these, 3100 (11 %) had a gluten content exceeding 20 mg/kg, 359 samples (1.3 %) contained >80 mg/kg, and 142 samples (0.51 %) > 200 mg/kg. After excluding two potentially biased studies, conservative descriptive analysis of 15,467 samples revealed that 20 % of analyzed samples showed contamination >20 mg/kg (crude pooling). Oats showed the highest average cross-contamination and variability, while restaurant meals demonstrated the greatest inconsistency. We identified research gaps and inconsistent terminology use, leading us to propose a standardized definition of "cross-contamination."

Cross-contact occurs in approximately 20 % of samples, but clinically relevant levels (>200 mg/kg) are rare (0.9 %). Regular portions (100-300 g) of foods >200 mg/kg could exceed the 10 mg/day safety threshold. Our findings suggest strict avoidance of all cross-contact could be reconsidered. A nuanced approach discussing relevant sources while identifying clinically irrelevant ones could prevent maladaptive eating behaviors without compromising safety.