Randomised controlled trialindependent cross-checkabstract checked★ key study I-WHT-101 in-depth review
White and whole-wheat flour leave the stomach at the same speed
Matched whole grain wheat and refined wheat milled products do not differ in glycemic response or gastric emptying in a randomized, crossover trial.
Overview
Pletsch EA et al.. Am J Clin Nutr 2022 · PMID 34999739 · DOI 10.1093/ajcn/nqab434
In a randomised trial with matched porridges, refined and whole-wheat flour did not differ in gastric emptying or blood sugar.
Does the study support the specific claim? No · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Compare refined and whole wheat digestion.
- How was the study done?
Randomised crossover.
- How many people, animals or samples were studied?
16 healthy adults.
- What was actually found?
No difference in gastric emptying.
- How large was the observed effect?
Bayes factors favour no effect.
- What do the results mean in everyday life?
White flour does not block the stomach.
- What are the study's limitations?
Small; porridge.
- What does it say about Elawady's specific claim?
Contradicts the glue mechanism.
- Do the results apply to Germany and Europe?
High.
- What can explicitly not be concluded from this study?
Does not test people with reflux.
Scientific in-depth review
1. Full reference
- Authors
- Pletsch EA et al.
- Journal
- Am J Clin Nutr
- Year
- 2022
- Identifier
- PMID 34999739 DOI 10.1093/ajcn/nqab434
- Verification
- verified – PubMed efetch 2026-10-26; Crossref works API 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
not stated in abstract
2. Research question
Do whole-grain and refined wheat milled products differ in glycaemic response or gastric emptying when food form is matched?
3. Study design and population
- Study design
- Randomised controlled trial – Randomised crossover trial, six matched wheat porridges
- Population
Healthy adults
- Country
not stated in abstract
- Period
not stated in abstract
- Sample size
16
- Inclusion and exclusion criteria
Healthy participants
4. Methods and endpoints
- Exposure / intervention
Whole wheat flour, cracked wheat, semolina, flour with fine or coarse bran
- Comparator
Refined wheat flour porridge (same grain source and mill)
- Endpoints
Postprandial glycaemia (CGM), gastric emptying (13C-octanoic acid breath test), appetite (VAS)
- Statistical methods
Mixed models; Bayes factors for null effects
5. Actual results
- Results
Little-to-no differences in glycaemic responses (lower iAUC only for semolina, MD -966 mg min/dL, and cracked wheat, MD -721, vs whole wheat flour porridge). Bayes factors suggested weak to strong evidence for no effect of treatment type on glycaemic response, gastric emptying and appetite.
- Absolute risks
not reported
- Authors' conclusion
Whole-grain wheat foods did not confer lower postprandial glycaemia or gastric emptying than matched refined wheat.
6. Strengths
- Randomised crossover
- Matched food form and grain source
- Bayesian inference for null
7. Weaknesses
- Small (n=16)
- Healthy volunteers
- Breath test, not scintigraphy
- Porridge, not bread
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
Small sample; blinding of food type difficult.
9. Assessment of the statistical interpretation
Evidence for absence of a difference in gastric emptying between refined and whole wheat.
10. Relevance to the specific claim
Directly tests whether refined wheat behaves differently in the stomach: gastric emptying did not differ, contrary to the claim that refined flour impairs stomach function.
11. Independent contrary findings
Coletta 2016 (I-WHT-103) found more heterogeneous chyme with high gluten bread, but no difference in emptying.
12. Transferability to Germany and Europe
High.
13. Overall methodological judgement
Small but direct physiological test against the mechanism.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | low |
| Directness | direct |
| Reproducibility | not replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Bread form; people with reflux.
15. Linked fact checks
- Refined white flour turns into a sticky glue-like paste in the stomach, sticks to the stomach wall, impairs stomach contractions and thereby causes reflux and indigestion, whereas whole-grain flour does not stick and is digested easily. – Studies contradicting or limiting the claim
- Commercial 'brown' or whole-wheat toast (brand named: Rich Bake) is allowed because, although it contains white flour and gluten, it is made in an easy-to-digest form that does not stick in the colon. – Studies with mixed or unclear results