Oxalate-rich greens (spinach, beet greens, chard) cause kidney stones; each 100 mg of dietary oxalate raises urinary oxalate by about 2.7 mg.

Original statement

No Arabic original wording available.

Translation

Oxalate-rich greens (spinach, beet greens, chard) cause kidney stones; each 100 mg of dietary oxalate raises urinary oxalate by about 2.7 mg.

Origin

Source status

Archive editors

Attribution

Archive editors

Origin

https://eltayebat.com/rule/leafy-greens-cucurbits/

Attribution uncertainty

Archive editorial text and study selection written by the archive operators, not necessarily by Elawady.

Claimed mechanism

Dietary oxalate increases urinary oxalate and calcium-oxalate crystallisation.

Claimed health effect

Kidney stones.

Population concerned

Everyone

Geographic restriction by Elawady

none found

Scientific assessment

Mostly false – Essential parts of the statement are not supported by the evidence or are strongly exaggerated.

Certainty of evidence: moderate – Further research may still affect the assessment.

1. What was claimed?

Oxalate-rich greens cause kidney stones.

2. What is demonstrably correct?

Spinach is the main oxalate source; high spinach intake (>=8 servings/month) was modestly associated with stones in men (RR 1.30) and older women (RR 1.34). Dietary oxalate contributes to urinary oxalate (Crivelli 2020; Holmes 2001, I-VEG-118: 24-42% of urinary oxalate on controlled diets). The archive's figure is correctly reproduced: in controlled diets, urinary oxalate rises by about 2.7 mg per 100 mg of dietary oxalate within 50-750 mg/day (Mitchell et al., I-VEG-116, as cited in Bargagli 2020). Calcium oxalate stone formers with high urinary oxalate are advised to moderate oxalate-rich foods.

3. What is wrong or exaggerated?

The cohort authors concluded that the data 'do not implicate dietary oxalate as a major risk factor'; in free-living people the highest vs lowest quartile of dietary oxalate differed by only 1.7 mg/day in urinary oxalate (Taylor 2008, I-VEG-117). A vegetable- and legume-rich DASH diet was associated with markedly fewer stones (RR 0.55-0.60). Boiling removes 30-87% of soluble oxalate (Chai 2005, I-VEG-119), and eating calcium with meals reduces absorption. The archive's cited J Urol study is an animal model with an oxalate precursor, not green vegetables.

4. What remains unclear?

The effect of very high spinach intake in specific populations (e.g. hot climates) is uncertain.

5. Which studies support it?

Mitchell 2019 (I-VEG-116, 2.7 mg per 100 mg); Taylor 2007 (modest association); Holmes 2001 (I-VEG-118); Khan 2007 (rat model).

6. Which studies contradict it?

Taylor 2007 (conclusion); Taylor 2008 (I-VEG-117, small effect on urinary oxalate); Taylor 2009 (DASH); Chai 2005 (I-VEG-119, cooking).

7. What applies to Germany and Europe?

Kidney-stone guidance in Europe advises adequate fluid and calcium, with oxalate moderation for recurrent stone formers.

8. What is known about Egypt?

Kidney stones are common in Egypt; hydration is the key preventive measure (not reviewed in detail).

9. What practical conclusion is appropriate?

For most people, eating greens does not meaningfully increase stone risk; stone formers should get individual advice.

Assessment details

Rationale for certainty of evidence

Large cohorts (240,000 participants) found only a modest association between oxalate intake and stones in men and older women (RR ~1.2), none in younger women; the authors concluded that dietary oxalate is not a major risk factor. A DASH-style diet rich in vegetables and legumes was associated with 40-45% lower stone risk.

Source quality

The archive's 2.7 mg figure does not appear in the abstract of the cited J Urol paper, which is a rat study using hydroxy-L-proline, not a human dietary-oxalate study.

Regional transferability

US cohorts; transferable to Germany and Egypt with caution (Egypt has high stone prevalence linked to climate and fluid intake; not reviewed).

Individual exceptions

Recurrent calcium-oxalate stone formers, people with enteric hyperoxaluria or CKD may need to limit high-oxalate foods individually and ensure adequate calcium.

Regional scope of the claim

general (biological/medical)

Last reviewed

26 October 2026 provisional

Scientific evidence in detail

Overinterpreted – A real finding exists, but the claim draws more from it than the data allow (e.g. association taken as cause, animal data applied to humans, small effect presented as large).

Research question: Do oxalate-rich greens cause kidney stones in the general population, and does each 100 mg dietary oxalate raise urinary oxalate by about 2.7 mg?

Study results as reported by the authors. Our assessment follows below.

Open questions

Effect in people with primary hyperoxaluria (reported in Egyptian families) - an individual exception requiring medical advice.

How deeply was this checked?

8 linked studies: 0 checked in full text (0 of them with a structured risk-of-bias assessment), 8 on the basis of the abstract, 0 bibliographically only. No formal assessment with two independent reviewers and no independent human expert review has taken place yet.

Last scientific review: 26 October 2026

In plain language

Spinach and some other greens contain oxalate, a substance found in most kidney stones. In large studies, people who ate the most oxalate had only a slightly higher risk of stones, and the authors concluded that dietary oxalate is not a major risk factor. People eating a diet rich in vegetables, fruit and legumes actually had far fewer kidney stones. The animal study cited by the archive does not test vegetables.

Studies on this claim

Regional context

Germany / EU

Kidney-stone guidance in Europe advises adequate fluid and calcium, with oxalate moderation for recurrent stone formers.

Egypt

Kidney stones are common in Egypt; hydration is the key preventive measure (not reviewed in detail).

• Pesticide residues in fruit and vegetables on the EU/German market (incl. imports from Egypt)
• Pesticide residues in produce sold on the Egyptian domestic market
• Nitrate in leafy vegetables
• Microbiological safety of fresh produce, herbs and spices

What applies in my country?

General scientific assessment

Mostly false The 2.7 mg figure is correct, but greens do not generally cause kidney stones; oxalate moderation is advice for stone formers.

The following areas of food safety are relevant to this statement:

• Pesticides and pesticide residues
• Contaminants (heavy metals, PFAS, PCBs, dioxins, nitrate)
• Pathogens (Salmonella, Campylobacter, etc.)

Fruit and vegetables

Limits: legal rules describe what is allowed, not what every single food contains. Measurement data come from samples and are meaningful only together with their method details.

Country of residence or purchase Compare with another country

References

1. Dietary oxalate and calcium oxalate nephrolithiasis.. Khan SR et al.. J Urol 2007 · PMID 17870111 · DOI 10.1016/j.juro.2007.06.046
2. Dietary oxalate and kidney stone formation.. Mitchell T et al.. Am J Physiol Renal Physiol 2019 · PMID 30566003 · DOI 10.1152/ajprenal.00373.2018
3. Oxalate intake and the risk for nephrolithiasis.. Taylor EN, Curhan GC. J Am Soc Nephrol 2007 · PMID 17538185 · DOI 10.1681/ASN.2007020219
4. DASH-style diet associates with reduced risk for kidney stones.. Taylor EN et al.. J Am Soc Nephrol 2009 · PMID 19679672 · DOI 10.1681/ASN.2009030276
5. Determinants of 24-hour urinary oxalate excretion.. Taylor EN et al.. Clin J Am Soc Nephrol 2008 · PMID 18650406 · DOI 10.2215/CJN.01410308
6. Effect of different cooking methods on vegetable oxalate content.. Chai W et al.. J Agric Food Chem 2005 · PMID 15826055 · DOI 10.1021/jf048128d
7. Contribution of Dietary Oxalate and Oxalate Precursors to Urinary Oxalate Excretion.. Crivelli JJ et al.. Nutrients 2020 · PMID 33379176 · DOI 10.3390/nu13010062
8. Contribution of dietary oxalate to urinary oxalate excretion.. Holmes RP et al.. Kidney Int 2001 · PMID 11135080 · DOI 10.1046/j.1523-1755.2001.00488.x