Systematic reviewindependent cross-checkabstract checked I-FAST-117 standard review
Does food variety protect health?
Systematic review of diet quality scores including diet diversity in relation to major chronic diseases, obesity and mortality in healthy adults.
Overview
Nickel DV et al.. Eur J Nutr 2026 · PMID 42047829 · DOI 10.1007/s00394-026-03907-x
Studies on diet variety and disease gave inconsistent results.
Does the study support the specific claim? Unclear · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Review diversity-containing diet scores.
- How was the study done?
Systematic review of 16 cohort reports.
- How many people, animals or samples were studied?
Healthy Western adults.
- What was actually found?
Inconsistent associations.
- How large was the observed effect?
Not pooled.
- What do the results mean in everyday life?
What and how much you eat overall matters more than how foods are combined in one meal.
- What are the study's limitations?
Heterogeneous measures.
- What does it say about Elawady's specific claim?
Neither supports nor refutes single-dish meals directly.
- Do the results apply to Germany and Europe?
Applies; same physiology.
- What can explicitly not be concluded from this study?
Effects of meal composition rules.
Scientific in-depth review
1. Full reference
- Authors
- Nickel DV et al.
- Journal
- Eur J Nutr
- Year
- 2026
- Identifier
- PMID 42047829 DOI 10.1007/s00394-026-03907-x
- Verification
- verified – PubMed efetch 2026-10-26; Crossref update-to/updated-by check
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
No conflicts declared.
2. Research question
Are diet quality scores with a diet-diversity component associated with chronic disease and mortality?
3. Study design and population
- Study design
- Systematic review – Systematic review of prospective studies (narrative synthesis)
- Population
Healthy adults in high-income Western countries
- Country
Western high-income countries
- Period
Search to Oct 2025
- Sample size
16 reports; 8 scores
- Inclusion and exclusion criteria
not stated in abstract
4. Methods and endpoints
- Exposure / intervention
Diet quality scores including diversity
- Comparator
Lower scores
- Endpoints
T2D, cancer, CVD, obesity, all-cause mortality
- Statistical methods
Narrative (heterogeneity)
5. Actual results
- Results
Associations with all-cause mortality (n=5), cancer (n=4), CVD (n=3), obesity (n=4) and T2D (n=3) were inconsistent, with null or inverse relationships.
- Absolute risks
not reported
- Authors' conclusion
Evidence remains insufficient to determine whether diet quality scores that include diet diversity are linked to chronic disease outcomes.
6. Strengths
- Recent systematic search
7. Weaknesses
- Heterogeneous definitions of diversity
- Only PubMed/NCBI searched
8. Risk of bias
- Orienting tool
- AMSTAR 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Single database; narrative synthesis.
9. Assessment of the statistical interpretation
No pooled estimate.
10. Relevance to the specific claim
Fairness check: the opposite position (that variety itself protects health) is also not well proven; quality and adequacy of the diet matter more than mixing rules.
11. Independent contrary findings
12. Transferability to Germany and Europe
Universal biology; applies in Europe and Egypt.
13. Overall methodological judgement
Indirect; shows the evidence on diversity is inconclusive, so neither 'never mix' nor 'always vary' is proven.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | not applicable |
| Directness | indirect |
| Reproducibility | unknown |
| Consistency with the overall evidence | inconsistent |
| Regional transferability | moderate |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
- Meals should consist of a single dish without mixing different foods; a single dish of allowed food is enough to live on. – Studies with mixed or unclear results