Tier 4 — mechanistic

Dietary Influences on Urinary Oxalate and Risk of Kidney Stones

Linda K. Massey

Frontiers in Bioscience 2003 8:s584-594

Bibliography

PubMed: PMID 12700096
DOI: 10.2741/1082
Funding: Not stated in the published article. No sponsor or funding source is declared.
Competing interests: Not stated in the published article. No formal conflict-of-interest statement is included; the article predates near-universal COI disclosure requirements.

Study snapshot

Design	Narrative review of endogenous oxalate synthesis, dietary oxalate absorption, and stone-former risk factors
Model	Not applicable — review synthesising multiple human epidemiological and metabolic-balance studies
Sample	Not applicable — review article; individual cited studies range from single-digit metabolic-ward cohorts to prospective cohorts of tens of thousands
Intervention	Not applicable — no intervention tested; reviews the effects of dietary oxalate load, dietary protein, ascorbate supplementation and calcium co-ingestion on urinary oxalate
Duration	Not applicable
Endpoints	Urinary oxalate excretion (mg/day); Proportion of urinary oxalate derived from diet vs endogenous synthesis; Calcium oxalate stone recurrence risk

What the study showed, in plain terms

This is a narrative review of where the oxalate in urine comes from, and what raises calcium oxalate kidney stone risk. It isn't a collagen study — it's included as safety-context background, because hydrolysed collagen is rich in glycine, and glycine is a metabolic precursor the body can convert into oxalate.

The review's headline point is that 40-50% of urinary oxalate in people eating a typical diet comes from food, not the body's own synthesis. A subgroup of "hyperabsorbers" exists among stone-formers, who take up more dietary oxalate than most people and benefit most from oxalate restriction.

The paper does not test collagen, gelatin, or glycine-rich supplements specifically. Readers asking whether a high daily dose of hydrolysed collagen could meaningfully raise oxalate and kidney stone risk will not find a direct answer here — that is a genuine evidence gap this review helps frame but does not close.

Key findings

40-50% of urinary oxalate in healthy people eating typical diets (150-250 mg/day dietary oxalate) originates from the diet itself; the remainder is endogenous synthesis, which is proportional to lean body mass and cannot be reduced by treatment.
Absorption of oxalate from food is typically only 3-8% of the food's total oxalate content in non-stone-formers, but a subpopulation of "hyperabsorbers" is found in most stone-former cohorts.
Increased dietary protein intake has been linked to increased urinary oxalate in some studies, though findings are inconsistent across the literature reviewed.
Simultaneous consumption of calcium-rich food reduces oxalate absorption from a meal by binding oxalate in the gut before it reaches the bloodstream.
High-dose vitamin C (ascorbate) supplementation above roughly 1-2 g/day can raise urinary oxalate, particularly in stone-formers, via non-enzymatic conversion of ascorbate to oxalate.
At least one-third of the stone-forming population studied absorbs more than 10% of ingested oxalate, and dietary oxalate restriction is recommended especially for this hyperoxaluric subgroup.

What this study can and cannot tell us

Published in 2003 and does not address collagen, gelatin, or glycine-rich protein supplements at any dose — the relevance to hydrolysed collagen peptide supplementation is inferential, not direct.
As a narrative (non-systematic) review, study selection and weighting are not governed by a pre-specified protocol, unlike a systematic review or meta-analysis.
Much of the underlying primary literature cited is decades old and used varied, sometimes dated, oxalate-measurement methodology (enzymatic assay vs HPLC/ion chromatography), which the author herself flags as a source of measurement error.
No data are presented on whether the glycine content of hydrolysed collagen supplements meaningfully increases endogenous oxalate synthesis at typical supplemental doses (2.5-20 g/day) — this remains an open question for the site's safety coverage.

Tier 3

Relationship of Protein Intake to Urinary Oxalate and Glycolate Excretion

Ross P. Holmes et al. · Kidney International · 1993

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Last verified 31 August 2026

Dr. Khaled Mahmoud, MBBChCritical Care Medicine, Longevity Science & Editorial Direction

Dr. Amr Yasser, PhDCardiometabolic, Musculoskeletal, Gut & Bioavailability

Dr. Abdulla Mostafa, PhDCellular Senescence, Neurological, Mitochondrial & Brain-Ageing Biology