Cross-sectional studyindependent cross-checkabstract checked★ key study I-VEG-117 standard review

Usual dietary oxalate changes urine oxalate only a little

Determinants of 24-hour urinary oxalate excretion.

Overview

Taylor EN et al.. Clin J Am Soc Nephrol 2008 · PMID 18650406 · DOI 10.2215/CJN.01410308

People eating the most oxalate excreted only 1.7 mg/day more oxalate than those eating the least.

Does the study support the specific claim? No · Methodological quality: moderate

Study explained simply

What did the researchers want to find out?: Find determinants of urinary oxalate.
How was the study done?: Cross-sectional cohort analysis.
How many people, animals or samples were studied?: 3,348 adults.
What was actually found?: Small dietary oxalate effect; vitamin C, BMI, diabetes matter.
How large was the observed effect?: +1.7 mg/d (Q4 vs Q1).
What do the results mean in everyday life?: Ordinary amounts of greens hardly change kidney-stone chemistry.
What are the study's limitations?: Cross-sectional; imprecise intake.
What does it say about Elawady's specific claim?: Limits the claim.
Do the results apply to Germany and Europe?: Transferable.
What can explicitly not be concluded from this study?: Cannot exclude effects of very high intakes.

Authors: Taylor EN et al.
Journal: Clin J Am Soc Nephrol
Year: 2008
Identifier: PMID 18650406 DOI 10.2215/CJN.01410308
Verification: verified – PubMed efetch 2026-10-26; Crossref 2026-10-26
Retracted: no
Corrections: none
Extent checked: abstract only
Conflicts of interest and funding: Funding (PubMed grant list): NCI NIH HHS; NIDDK NIH HHS

What determines 24-h urinary oxalate excretion?

Study design: Cross-sectional study – Cross-sectional analysis of 24-h urine collections in three cohorts (HPFS, NHS I, NHS II)
Population: Stone formers and non-stone formers from US health-professional cohorts
Country: USA
Period: not stated in abstract
Sample size: 3,348
Inclusion and exclusion criteria: not stated in abstract

Exposure / intervention: Dietary oxalate, vitamin C, calcium, fructose, BMI, diabetes, urinary factors
Comparator: Quartiles
Endpoints: 24-h urinary oxalate
Statistical methods: Multivariable regression across quartiles

Results: Median urinary oxalate 39 mg/d (men), 27 (older women), 26 (younger women). Highest vs lowest quartile of dietary oxalate: +1.7 mg/d urinary oxalate (P trend 0.001); vitamin C >=1,000 mg/d: +6.8 mg/d; calcium intake and age inversely associated; diabetes +2.0 mg/d.
Absolute risks: not reported
Authors' conclusion: The impact of dietary oxalate on urinary oxalate appears to be small.

+1.7 mg/d equals 4-7% of median excretion (stats/C-VEG-05_oxalate.py).

Limits the claim: in everyday diets, dietary oxalate shifts urinary oxalate only slightly.

Holmes 2001 controlled diets show a larger dietary share.

US data; physiology transferable.

Together with Taylor 2007 (I-VEG-05), supports that greens are not a major stone driver for most people.

Multidimensional assessment
Multidimensional assessment
Authenticity of the source	verified
Methodological quality	moderate
Risk of bias	some concerns
Precision of results	moderate
Directness	direct
Reproducibility	partly replicated
Consistency with the overall evidence	mixed
Regional transferability	moderate
Adequacy of the interpretation (by the archive)	not applicable

Measurement-error-corrected estimates.