Randomised controlled trialindependent cross-checkabstract checked★ key study I-GRN-102 in-depth review
Expecting gluten causes more symptoms than gluten itself
The effect of expectancy versus actual gluten intake on gastrointestinal and extra-intestinal symptoms in non-coeliac gluten sensitivity: a randomised, double-blind, placebo-controlled, international, multicentre study.
Overview
de Graaf MCG et al.. Lancet Gastroenterol Hepatol 2024 · PMID 38040019 · DOI 10.1016/S2468-1253(23)00317-5
People with self-reported gluten sensitivity had the most symptoms when they expected and got gluten; gluten given without that expectation caused no extra symptoms.
Does the study support the specific claim? Partly · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Separate the effect of expecting gluten from eating it.
- How was the study done?
Randomised double-blind trial with four groups.
- How many people, animals or samples were studied?
83 adults with self-reported gluten sensitivity.
- What was actually found?
Expectation mattered more than gluten.
- How large was the observed effect?
Difference up to 9.6 mm on a 100 mm scale.
- What do the results mean in everyday life?
Belief and anxiety contribute strongly to symptoms.
- What are the study's limitations?
One-day test, small groups, industry co-funding.
- What does it say about Elawady's specific claim?
Supports that much non-coeliac gluten sensitivity is not gluten-specific.
- Do the results apply to Germany and Europe?
High.
- What can explicitly not be concluded from this study?
Cannot rule out a small gluten effect and says nothing about coeliac disease.
Scientific in-depth review
1. Full reference
- Authors
- de Graaf MCG et al.
- Journal
- Lancet Gastroenterol Hepatol
- Year
- 2024
- Identifier
- PMID 38040019 DOI 10.1016/S2468-1253(23)00317-5
- Verification
- verified – PubMed efetch 2026-10-26; Crossref works API 2026-10-26
- Retracted
- no
- Corrections
Erratum published: Lancet Gastroenterol Hepatol 2024;9(3):e8 (doi 10.1016/S2468-1253(24)00014-1); content not read.
- Extent checked
- abstract only
- Conflicts of interest and funding
Public-private partnership funding including bakery and cereal industry partners (AB Mauri, Fazer, Mondelez, International Wheat Gluten Association and others); one author employed by the bread supplier. Funding statement in PubMed record.
2. Research question
Do expectancy and actual gluten intake affect symptoms in self-reported NCGS?
3. Study design and population
- Study design
- Randomised controlled trial – Randomised, double-blind, placebo-controlled, 2x2 factorial (expectancy x actual gluten) multicentre trial
- Population
Adults 18-70 years with self-reported NCGS, coeliac disease and wheat allergy excluded, asymptomatic on a gluten-free diet
- Country
UK, Netherlands
- Period
2018-2022
- Sample size
84 randomised; 83 per-protocol
- Inclusion and exclusion criteria
Self-reported GI symptoms within 8 h of gluten; gluten-free/restricted diet; VAS <=30 mm
4. Methods and endpoints
- Exposure / intervention
Expectation of gluten (E+) and/or actual gluten (G+) in oat bread
- Comparator
Gluten-free oat bread and/or expectation of gluten-free bread
- Endpoints
Overall GI symptom score (VAS) over 8 h
- Statistical methods
Per-protocol comparisons of mean VAS between four groups
5. Actual results
- Results
Mean overall GI symptom score: E+G+ 16.6 mm (13.1-20.0), E-G+ 6.9 (3.5-10.4), E-G- 7.4 (4.2-10.7), E+G- 11.7 (8.3-15.1). E+G+ vs E-G+ difference 9.6 mm (3.0-16.2), p=0.0010; E+G+ vs E-G- 9.1 (2.7-15.6), p=0.0016; E+G+ vs E+G- 4.9 (-1.7 to 11.5), p=0.28; E-G+ vs E-G- -0.5 (-7.0 to 5.9), p=1.0.
- Absolute risks
not applicable
- Authors' conclusion
Expectancy plus actual gluten had the largest effect, reflecting a nocebo effect, although an additional effect of gluten cannot be ruled out.
6. Strengths
- Factorial design separating expectancy from gluten
- Double-blind for gluten content
- Registered (NCT05779358)
7. Weaknesses
- Single-day challenge
- Per-protocol analysis
- Small groups (~20 each)
- Substantial wheat-industry funding (results do not obviously favour industry, but noted)
8. Risk of bias
- Orienting tool
- RoB 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Per-protocol analysis and industry co-funding; randomisation and blinding appropriate.
9. Assessment of the statistical interpretation
Gluten without negative expectation produced no symptom increase (difference -0.5 mm); differences are small in absolute VAS terms.
10. Relevance to the specific claim
Supports the idea that symptoms attributed to gluten in self-reported NCGS are largely driven by expectation.
11. Independent contrary findings
I-GRN-103 (biomarker evidence of a subgroup with immune activation).
12. Transferability to Germany and Europe
High (European trial).
13. Overall methodological judgement
Well-designed but small trial; supports a nocebo explanation for most NCGS symptoms.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | low |
| Directness | direct |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Longer challenges; gut-brain mechanisms.
15. Linked fact checks
- 'There is no such thing as gluten sensitivity'; the real problem is only that white flour turns into a glue-like substance. – Studies supporting the claim