Randomised controlled trialindependent cross-checkabstract only checked I-GUT-08 standard review
Fermented foods and the immune system
Gut-microbiota-targeted diets modulate human immune status.
Overview
Wastyk HC et al.. Cell 2021 · PMID 34256014 · DOI 10.1016/j.cell.2021.06.019
Fermented foods increased gut bacterial diversity and lowered inflammation markers in a small trial.
Does the study support the specific claim? No · Methodological quality: low
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Diet–microbiome.
- How was the study done?
Small RCT.
- How many people, animals or samples were studied?
36.
- What was actually found?
Diversity up, inflammation down.
- What do the results mean in everyday life?
Fermentation can be beneficial.
- What are the study's limitations?
Very small.
- What does it say about Elawady's specific claim?
Contradicts C-GUT-05.
- Do the results apply to Germany and Europe?
Applicable.
- What can explicitly not be concluded from this study?
Clinical outcomes.
Scientific in-depth review
1. Full reference
- Authors
- Wastyk HC et al.
- Journal
- Cell
- Year
- 2021
- Identifier
- PMID 34256014 DOI 10.1016/j.cell.2021.06.019
- Verification
- verified – PubMed efetch 2026-10-25
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
Declaration of interests H.C.W. is a founder and shareholder of Interface Biosciences. W.V.T. is a founder and shareholder of Interface Biosciences. J.L.S. is a founder, shareholder, and on the scientific advisory board of January AI and Novome Biotechnologies.
2. Research question
Effects of high-fibre vs high-fermented-food diets on microbiome and immune status
3. Study design and population
- Study design
- Randomised controlled trial – Randomised prospective diet intervention study (17 weeks)
- Population
Healthy adults
- Country
USA
- Period
17 weeks
- Sample size
18 per arm
- Inclusion and exclusion criteria
Healthy adults
4. Methods and endpoints
- Exposure / intervention
High-fermented-food diet
- Comparator
High-fibre diet
- Endpoints
Cytokine response score; microbiome; immune markers
- Statistical methods
-omics
5. Actual results
- Results
Fermented-food diet steadily increased microbiota diversity and decreased inflammatory markers; high-fibre diet increased glycan-degrading enzymes with stable diversity; primary outcome unchanged.
- Absolute risks
not applicable
- Authors' conclusion
Fermented foods may help counter decreased diversity and increased inflammation.
6. Strengths
- Deep profiling
7. Weaknesses
- Very small
- Primary outcome null
- Authors' COI (company founders)
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; no placebo; COI.
9. Assessment of the statistical interpretation
10. Relevance to the specific claim
11. Independent contrary findings
12. Transferability to Germany and Europe
US.
13. Overall methodological judgement
Hypothesis-generating; fermentation not harmful.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | low |
| Risk of bias | some concerns |
| Precision of results | low |
| Directness | indirect |
| Reproducibility | not replicated |
| Consistency with the overall evidence | unknown |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
- Residues of incomplete digestion and the fermentation of hard-to-digest food in the gut are harmful waste that stimulates the immune, nervous and hormonal systems. – Studies contradicting or limiting the claim