Meta-analysisindependent cross-checkabstract checked★ key study I-VEG-01 in-depth review
Fibre and health (Lancet 2019)
Carbohydrate quality and human health: a series of systematic reviews and meta-analyses.
Overview
Reynolds A et al.. Lancet 2019 · PMID 30638909 · DOI 10.1016/S0140-6736(18)31809-9
High fibre intake is linked to 15-30% lower death and disease rates; trials show better weight, blood pressure and cholesterol.
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?
Fibre and NCDs
- How was the study done?
Meta-analyses
- How many people, animals or samples were studied?
185 cohorts, 58 RCTs
- What was actually found?
Large benefits
- How large was the observed effect?
15-30% lower risk
- What do the results mean in everyday life?
Eat 25-29 g fibre daily.
- What are the study's limitations?
Observational endpoints
- What does it say about Elawady's specific claim?
Contradicts 'cattle food'
- Do the results apply to Germany and Europe?
High
- What can explicitly not be concluded from this study?
Not specific to leafy greens.
Scientific in-depth review
1. Full reference
- Authors
- Reynolds A et al.
- Journal
- Lancet
- Year
- 2019
- Identifier
- PMID 30638909 DOI 10.1016/S0140-6736(18)31809-9
- Verification
- verified – PubMed efetch 2026-10-25
- Retracted
- no
- Corrections
Erratum published (Lancet 2019;393:406)
- Extent checked
- abstract only
- Conflicts of interest and funding
Health Research Council of New Zealand, WHO and others
2. Research question
Carbohydrate quality markers (fibre, whole grains, GI) and NCD outcomes.
3. Study design and population
- Study design
- Meta-analysis – Series of systematic reviews and meta-analyses of prospective studies and RCTs (GRADE)
- Population
Adults without chronic disease
- Country
Multiple
- Period
Cohorts to April 2017; RCTs to Feb 2018
- Sample size
185 prospective studies (~135 million person-years); 58 RCTs (4,635 adults)
- Inclusion and exclusion criteria
Excluded chronic disease, weight-loss and supplement trials
4. Methods and endpoints
- Exposure / intervention
Higher dietary fibre
- Comparator
Lower fibre
- Endpoints
Mortality, CHD, stroke, T2D, colorectal cancer; risk factors
- Statistical methods
Random effects; dose-response; GRADE
5. Actual results
- Results
Highest vs lowest fibre: 15-30% decrease in all-cause and CV mortality, CHD, stroke, T2D, colorectal cancer; RCTs: lower body weight, systolic BP, total cholesterol; greatest risk reduction at 25-29 g/day; certainty moderate for fibre.
- Absolute risks
not reported
- Authors' conclusion
Relationships could be causal; increasing fibre expected to benefit health.
6. Strengths
- Large
- Cohorts + RCTs
- GRADE
7. Weaknesses
- Observational for hard endpoints
8. Risk of bias
- Orienting tool
- AMSTAR 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- low
- Rationale
High-quality review series.
9. Assessment of the statistical interpretation
Consistent dose-response.
10. Relevance to the specific claim
Contradicts the claim that non-digestible plant material is harmful.
11. Independent contrary findings
None.
12. Transferability to Germany and Europe
High.
13. Overall methodological judgement
Key evidence.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | low |
| Precision of results | high |
| Directness | indirect |
| Reproducibility | replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Fibre source-specific effects.
15. Linked fact checks
- Gas from legumes and greens distends the colon, keeps blood from reaching the brain and causes dizziness that is wrongly diagnosed as anaemia; the human body is not equipped to digest the hulls of fava beans, lentils or beans. – Studies contradicting or limiting the claim
- 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 contradicting or limiting the claim
- 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 contradicting or limiting the claim
- Avoiding (nearly) all vegetables, salads and legumes is compatible with good health. – Studies contradicting or limiting the claim