Overview

• A randomized, double-blind, sham-controlled crossover trial at McMaster University tracked 29 IBS patients over repeated challenges with gluten, wheat and placebo cereal bars.
• Symptom severity worsened at similar rates across all three bar types, implicating the nocebo effect rather than ingredient-specific sensitivity.
• Laboratory analysis of stool samples showed that only about one-third of participants actually consumed the assigned bars, suggesting some skipped challenges to avoid discomfort.
• Even after revealing which bars triggered reported symptoms, most participants maintained their gluten-free beliefs and continued avoidance behaviors.
• Study authors emphasize that declaring gluten safe is not enough and recommend counseling to destigmatize wheat and support safe reintroduction.