Othercited by the Tayebat archivefull text checked★ key study A-VEG-16 in-depth review
Cellulose-digesting gut bacteria
Cryptic diversity of cellulose-degrading gut bacteria in industrialized humans.
Overview
Moraïs S et al.. Science 2024 · PMID 38484069 · DOI 10.1126/science.adj9223
Humans carry cellulose-digesting bacteria; they are common in traditional populations and rare in industrialised ones.
Does the study support the specific claim? No · Methodological quality: high
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Map cellulose degraders
- How was the study done?
Metagenomics + biochemistry
- How many people, animals or samples were studied?
Not stated
- What was actually found?
Rare in industrialised humans
- How large was the observed effect?
Not applicable
- What do the results mean in everyday life?
Western lifestyle may reduce these microbes.
- What are the study's limitations?
No health data
- What does it say about Elawady's specific claim?
Does not support avoiding vegetables
- Do the results apply to Germany and Europe?
Moderate
- What can explicitly not be concluded from this study?
Cannot show vegetables are harmful.
Scientific in-depth review
1. Full reference
- Authors
- Moraïs S, Winkler S, Zorea A, Levin L, Nagies FSP, Kapust N, Lamed E, Artan-Furman A, Bolam DN, Yadav MP, Bayer EA, Martin WF, Mizrahi I
- Journal
- Science
- Year
- 2024
- Identifier
- PMID 38484069 DOI 10.1126/science.adj9223 · PMC7615765
- Verification
- verified – PubMed E-utilities efetch, 2026-10-25
- Retracted
- no
- Corrections
- none
- Extent checked
- full text
- Conflicts of interest and funding
German-Israeli Project Cooperation (DIP), European Research Council (ERC 866530, ERC-POC), Israel Science Foundation, National Institute of Biotechnology in the Negev; authors declare no conflicts of interest.
2. Research question
Which cellulosome-producing (cellulose-degrading) bacteria occur in the human gut, how did they originate, and how are they distributed across human lifestyles and animal hosts?
3. Study design and population
- Study design
- Other – Comparative metagenomic, phylogenetic and evolutionary analysis of cellulosome-producing ruminococci, with biochemical validation (cohesin-dockerin binding, recombinant cellulase/GH98 activity) and metatranscriptomics
- Population
Metagenome-assembled genomes (4941 rumen MAGs, 92,143 human MAGs) and 1989 gut metagenome samples from humans (industrialised, rural, hunter-gatherer, 1000-2000-year-old paleofaeces) and 75 animal species (non-human primates, ruminants)
- Country
Multiple (industrialised cohorts incl. Denmark, China, Sweden, USA; rural and hunter-gatherer cohorts worldwide)
- Period
Not applicable (analysis of existing metagenomic datasets; paleofaeces 1000-2000 years old)
- Sample size
62 ruminococcal genomes for phylogeny (25 rumen and 22 human MAGs >=90% complete plus 15 isolate genomes); 1989 gut samples for prevalence; 30 MAGs (14 rumen, 8 human, 8 NHP) for core-genome analysis
- Inclusion and exclusion criteria
MAGs with ScaC hits (E<10^-4, >45% identity, >250 aa) and >=90% CheckM completeness
4. Methods and endpoints
- Exposure / intervention
Host type and lifestyle (industrialised vs non-industrialised humans, primates, ruminants)
- Comparator
Across populations and host species
- Endpoints
Prevalence and abundance of cellulosome-producing species (Candidatus R. hominiciens, R. primaciens, R. ruminiciens); cellulosome assembly; enzymatic activity on microcrystalline cellulose and glucuronoarabinoxylan; gene expression
- Statistical methods
Maximum-likelihood phylogenetics, Mantel and AU tests, Wilcoxon tests, PERMANOVA, indicator-value tests, Kruskal-Wallis; mostly descriptive prevalence comparisons
5. Actual results
- Results
Three new cellulosome-producing human gut species identified; their cellulosomes assemble and a GH5 cellulase degrades microcrystalline cellulose. Collective prevalence at most 4.6% in industrialised cohorts vs 43% in paleofaeces, 21% in hunter-gatherers, 20% in rural societies, 41% in apes and 33% in other NHPs; abundance also lower in industrialised positives. Cellulosomal genes >90% expressed in host guts. Human-associated R. hominiciens carries a GH98 enzyme active on cereal (maize) glucuronoarabinoxylan. Authors link lower prevalence to low fibre intake (Hadza 80-150 g/day, rural 13-14 g/day, industrialised 8.4 g/day) and possibly antibiotics.
- Absolute risks
not applicable (no health outcomes)
- Authors' conclusion
Cellulose-degrading ruminococci were more widespread in the past and appear to be declining in industrialised populations, likely due to westernised lifestyle and low fibre intake, potentially affecting energy balance and health; reintroduction or enrichment via targeted diets and probiotics may be possible. Health impact requires future isolation and study.
6. Strengths
- Very large metagenomic resource
- Functional biochemical validation of cellulosome assembly and enzyme activity
- Multiple independent phylogenetic approaches
- Data deposited (GenBank, DRYAD)
7. Weaknesses
- No health outcomes and no measurement of actual cellulose fermentation in people
- Prevalence comparisons are ecological and confounded by diet, antibiotics, sequencing depth and cohort methods
- Species defined from MAGs only (Candidatus; not isolated)
- Evolutionary origin (ruminant transfer during domestication) is inferential; authors note cospeciation cannot be ruled out
- Diet-prevalence link inferred from literature fibre estimates, not individual data
8. Risk of bias
- Orienting tool
- none applicable (basic-science metagenomic/biochemical study)
- Type of assessment
- structured assessment based on the full text by a single reviewer (no formal double review)
- Full formal assessment
- no
- Overall risk of bias
- not assessable
- Rationale
No standard risk-of-bias tool fits; structured single-reviewer judgement from full text, not formal. Internal biochemical validity is high; population comparisons are descriptive.
| Domain | Judgement | Rationale |
|---|---|---|
| Sample representativeness | some concerns | Public metagenomes of heterogeneous cohorts; industrialised samples from a few countries. |
| Measurement validity (detection of species) | some concerns | Detection depends on MAG quality and read mapping; low-abundance taxa may be missed, especially in shallow metagenomes. |
| Confounding of population comparisons | high | Lifestyle groups differ in diet, antibiotics, geography and sequencing protocols; no adjustment. |
| Functional inference | low | Enzyme activity and cellulosome assembly verified biochemically. |
| Relevance to health claims | not applicable | No clinical endpoints. |
Full-text review (25 October 2026): Added sample sizes (92,143 human MAGs; 1989 samples), exact prevalences (<=4.6% industrialised vs 43%/21%/20%), fibre-intake explanation, authors' suggestion of dietary reintroduction, funding/COI (ERC, ISF, DIP; no conflicts); structured validity domains.
9. Assessment of the statistical interpretation
Descriptive prevalence differences (<=4.6% vs ~20-43%) without adjustment; cannot attribute causes or health consequences.
10. Relevance to the specific claim
Misused for C-VEG-01/02.
11. Independent contrary findings
Koh 2016; Reynolds 2019.
12. Transferability to Germany and Europe
Applies to industrialised populations.
13. Overall methodological judgement
Sound science, misinterpreted.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | not assessable |
| Precision of results | not applicable |
| Directness | very indirect |
| Reproducibility | unknown |
| Consistency with the overall evidence | unknown |
| Regional transferability | moderate |
| Adequacy of the interpretation (by the archive) | taken out of context |
14. Open questions
Whether these bacteria contribute measurably to energy harvest or health; whether higher fibre intake restores them.
15. Linked fact checks
- Humans, having a single stomach, cannot digest the cellulose in vegetables (unlike ruminants), so greens and legumes cause gas and bloating and are food made for animals, not for humans. – Studies with mixed or unclear results
- A 2024 Science paper shows that industrialised humans have lost the cellulose-degrading gut bacteria, so the modern human gut 'was never built to digest cellulose' and no longer carries the machinery to ferment plant cell walls. – Studies with mixed or unclear results
Use by the Tayebat archive
Note: according to the archive, the studies were compiled by the archive operators. Whether Dr. Elawady himself cited this study is not established.
- What the archive says about the study
Industrialised humans have almost entirely lost cellulose-degrading Ruminococcus; modern gut no longer equipped to ferment cellulose.
- A. What was actually studied?
Distribution of cellulose degraders.
- B. What did the authors find?
Humans carry functional cellulose-degrading gut bacteria; rare (<=4.6%) in industrialised populations, common (20-43%) in rural, hunter-gatherer and ancient samples; human strains adapted to cereal fibres.
- C. What conclusions do the authors themselves draw?
Decline is likely linked to low-fibre westernised diets and could potentially be reversed through targeted diets and probiotics.
- D. What does the archive derive from it?
Proof that the human gut was 'never built' to digest cellulose and vegetables are the wrong fuel.
- E. Is this derivation scientifically justified?
Not justified: the paper shows humans do harbour cellulose degraders (rare, not absent, in industrialised populations), attributes their rarity to low fibre intake, and suggests restoring them through diet - the opposite of concluding that vegetables are the wrong fuel. It concerns cellulose only and tests no health effects.
- Adequacy of the interpretation (by the archive)
- taken out of context