Narrative reviewindependent cross-checkabstract checked★ key study I-VEG-116 standard review
Dietary oxalate raises urinary oxalate
Dietary oxalate and kidney stone formation.
Overview
Mitchell T et al.. Am J Physiol Renal Physiol 2019 · PMID 30566003 · DOI 10.1152/ajprenal.00373.2018
About half of urinary oxalate comes from food; a cited controlled-diet estimate is 2.7 mg more urinary oxalate per 100 mg eaten.
Does the study support the specific claim? Partly · Methodological quality: low
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Review the role of dietary oxalate in stones.
- How was the study done?
Narrative review.
- How many people, animals or samples were studied?
Not applicable.
- What was actually found?
Diet contributes about half of urinary oxalate; restriction advised for stone formers.
- How large was the observed effect?
2.7 mg per 100 mg (cited).
- What do the results mean in everyday life?
Kidney-stone patients may need to limit spinach-type foods; others usually do not.
- What are the study's limitations?
Narrative.
- What does it say about Elawady's specific claim?
Number correct; general causal claim overstated.
- Do the results apply to Germany and Europe?
Universal.
- What can explicitly not be concluded from this study?
Cannot show that greens cause stones in healthy people.
Scientific in-depth review
1. Full reference
- Authors
- Mitchell T et al.
- Journal
- Am J Physiol Renal Physiol
- Year
- 2019
- Identifier
- PMID 30566003 DOI 10.1152/ajprenal.00373.2018
- Verification
- verified – PubMed efetch 2026-10-26; Crossref 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
COI statement: No conflicts of interest, financial or otherwise, are declared by the authors. | Funding (PubMed grant list): NIDDK NIH HHS
2. Research question
How does dietary oxalate contribute to urinary oxalate and stone growth?
3. Study design and population
- Study design
- Narrative review – Narrative review (urology/physiology) including controlled dietary oxalate-loading data
- Population
Humans; stone formers
- Country
USA (author affiliation)
- Period
not applicable
- Sample size
not applicable
- Inclusion and exclusion criteria
not stated in abstract
4. Methods and endpoints
- Exposure / intervention
Dietary oxalate
- Comparator
not applicable
- Endpoints
Urinary oxalate; calcium oxalate stone formation
- Statistical methods
Narrative
5. Actual results
- Results
About half of urinary oxalate derives from diet in normal individuals; urinary oxalate is a continuous risk factor; individuals excreting >25 mg/day may benefit from reduction. Per the full text of Bargagli 2020 (PMC7551439), Mitchell et al. report a 2.7 mg increase in urinary oxalate per 100 mg dietary oxalate within 50-750 mg/day on a 1,000 mg/day calcium diet (not visible in this abstract).
- Absolute risks
not reported
- Authors' conclusion
To limit calcium oxalate stone growth, patients should maintain hydration, avoid oxalate-rich foods and consume adequate calcium.
6. Strengths
- Experienced research group; includes controlled-diet data
7. Weaknesses
- Narrative review
- Full text not accessed; 2.7 mg figure taken from a secondary citation
8. Risk of bias
- Orienting tool
- none applicable
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Narrative review by advocates of oxalate restriction for stone formers.
9. Assessment of the statistical interpretation
Linear slope 2.7 mg per 100 mg implies ~6.8 mg/day more urinary oxalate at 250 mg/day dietary oxalate (stats/C-VEG-05_oxalate.py).
10. Relevance to the specific claim
Shows that the archive's 2.7 mg per 100 mg figure is a correct reproduction of the controlled-diet literature; advice applies to calcium oxalate stone formers.
11. Independent contrary findings
Taylor 2007/2008 cohorts: modest effect of dietary oxalate in free-living people.
12. Transferability to Germany and Europe
Universal physiology.
13. Overall methodological judgement
Supports the quantitative part of the claim and oxalate moderation for stone formers, not that greens cause stones in the general population.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | low |
| Risk of bias | some concerns |
| Precision of results | not applicable |
| Directness | direct |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | mixed |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Effect of realistic greens intake with adequate calcium.