Does a high-protein diet cause kidney stones?

No trial has shown that it does. What a high-protein diet reliably does is change the urine in the direction that favors stones. Across 30 studies in 2160 people without kidney disease, high-protein diets raised urinary calcium by about 25 mg a day against normal or low protein diets. In a two year trial of 307 adults with obesity, a low carbohydrate, high protein diet raised urinary calcium by about 36 percent, and no new kidney stones showed up clinically, though nobody scanned for them.

Established. High-protein diets raise the calcium in urine. A meta-analysis of 30 studies put the rise at 25.43 mg a day, with an interval from 13.62 to 37.24. A systematic review of popular diets adds that high protein diets also raise uric acid and lower urine pH and citrate. These are urine measurements that predict stones, and none of them is a stone.

Unsettled. Whether those urine changes turn into stones is not settled. An umbrella review for the German Nutrition Society found no evidence that higher protein intake specifically triggers kidney stones, and graded it possible that there is no link at all. The cohort data below point to meat rather than to protein as such.

What the trials found

The trials ran the question the other way round. They took people who had already had stones and asked them to eat less animal protein. On its own, that has not worked. A 2021 meta-analysis of six randomized trials found that a low protein diet, with or without extra fiber, did not reduce repeat calcium stones, with a risk ratio of 2.32 and an interval from 0.42 to 12.85. That interval is so wide that the result means no benefit was shown, and it does not mean harm.

Percent of stone formers who had another stone

Three randomized trials of eating less animal protein, each against its own comparison group. Only the first diet, which also cut salt and kept calcium normal, did better. The percentages come as reported, without intervals. Sources: cards ev-protks-04 and 11 below.

Two single trials show why. In one, 99 people after a first calcium oxalate stone were advised to eat less animal protein and more fiber for four and a half years. They had more repeat stones than people given fluid advice alone, 7.1 against 1.2 per 100 person-years, an adjusted risk ratio of 5.6 with an interval from 1.2 to 26.1. The fiber included bran, there were few stones in either group, and the interval is wide. In another, 175 calcium stone formers were randomized for four years. Only 73 finished, and among them 48 percent had another stone on a low animal protein diet and 48 percent on a normal diet.

The one diet that worked changed three things together. In a five year trial of 120 men with repeat calcium oxalate stones and high urine calcium, a diet with normal calcium, 52 g of animal protein a day and less salt lowered urinary oxalate by 7.2 mg a day, while a low calcium diet raised it by 5.4 mg. A Cochrane review of five trials in 379 adults concluded that five years on a normal calcium, low protein, low salt diet may reduce repeat stones in people with high urine calcium. Protein cannot be separated from salt and calcium in that result.

What the cohorts show

Risk of kidney stones in people eating more, observational studies

Observational data

Above 1 means more stones. Every row is observational and cannot show cause, and the authors rated their confidence in most of these links as low. Sources: cards ev-protks-06 and 08 below.

Across 14 prospective cohorts, people eating more processed meat, more meat in general and more animal protein from foods other than dairy had more kidney stones. Dairy protein went the other way. These are associations in people who had not had a stone, the authors rated confidence in most of them as low, and they found signs of publication bias. One meta-analysis of four cohorts, rated low certainty, put high animal protein intake at a 10 percent higher risk, and two other reviews found the risk inconclusive or absent.

Who should be careful

Not for everyone. The authors of the 30 study meta-analysis advise caution with high-protein weight loss diets built on animal protein in people with obesity, because kidney disease is common in that group. That is their advice, and it is not a measured risk of stones. Their data come from people without kidney disease, so they say nothing about how much protein is safe when the kidneys are already damaged.

We could not find a quotable protein limit for chronic kidney disease. The relevant guideline was not available to us in full, so if you have kidney disease, how much protein to eat is a question for the person treating you. For children with cystinuria, a rare inherited stone disease, an Italian urology guideline strongly advises less than 20 g of protein a day, less than 2 g of salt and more than 3.2 quarts (3 liters) of fluid, while admitting the evidence for it is weak.

What expert bodies say

The same Italian urology working group says a low to normal protein intake lowers the calcium in urine and could help prevent stones and keep bones strong. That is expert opinion. The German Nutrition Society review sits at the other end and found no evidence that higher protein triggers stones in people in general.

For the foods behind the cohort numbers, see meat.

How we searched

Searched: a local copy of the PubMed 2026 baseline, for protein, animal protein, meat and high-protein diets with kidney stones, nephrolithiasis, stone formers and urinary calcium. The broad query returned 753 records and we screened the top 45. A narrower query for protein restriction or high-protein diets and stone recurrence returned 44. We also searched for kidney disease nutrition guidelines, an AHRQ protein review, ClinicalTrials.gov and the open web. Search run on 7 October 2026.

Included: four meta-analyses and systematic reviews of trials, four randomized trials, a dose response meta-analysis of cohorts, an umbrella review, a systematic review of popular diets and an Italian urology guideline. None of the sources has been retracted.

Excluded: a five day study of 10 healthy men that measured only urine, an older review that called the evidence limited and inconsistent and added nothing newer, trials of plant protein and phosphate, and a review of vegan diets in children that was not about stones.

What we read: abstracts for most sources, and the full results section of the German umbrella review.

What we could not get: the full text of the 2020 kidney disease nutrition guideline, whose abstract gives no protein targets, and the full texts of three of the randomized trials.

What would change this answer

A long randomized trial of high against normal protein with stones confirmed on imaging as the result. The two year trial in adults with obesity counted only stones that caused symptoms.
A trial that changes animal protein without also changing fiber, salt or calcium, so that its own effect can be seen.
A protein recommendation for chronic disease. A recent AHRQ review was done for an update of the US protein requirements, and none has come out yet.

The rest of the nutrient, in one place. Protein: who genuinely needs more of it, and what the extra does not do → What it does, how much you need, who runs short, and what too much does, with the evidence level shown on every line.

The food behind this question

Meat: what the studies measured, and what they left out — numbers, evidence and safety

The full guide

Protein: who genuinely needs more of it, and what the extra does not do

The same question for other foods (kidney stones)

Sources

ev-protks-01 · Meta-analysis or systematic review · systematic review and meta-analysis of intervention studies · n = 30 studies, 2160 subjects
HP regimens resulted in a significantly more pronounced increase in glomerular filtration rate [MD: 7.18 ml/min/1.73 m2, 95% CI 4.45 to 9.91, p<0.001], serum urea [MD: 1.75 mmol/l, 95% CI 1.13 to 237, p<0.001], and urinary calcium excretion [MD: 25.43 mg/24h, 95% CI 13.62 to 37.24, p<0.001] when compared to the respective LP/NP protocol.
Who: subjects without chronic kidney disease
Effect: urinary calcium MD +25.43 mg/24h (95% CI 13.62 to 37.24); GFR MD +7.18 ml/min/1.73 m2
Certainty: Surrogate (urinary calcium), not stones; high heterogeneity of doses and durations.
PLoS One, 2014 · checked 2026-10-07 · we read the abstract
ev-protks-02 · Meta-analysis or systematic review · systematic review and meta-analysis · n = 30 studies, 2160 subjects
In the light of the high risk of kidney disease among obese, weight reduction programs recommending HP diets especially from animal sources should be handled with caution.
Who: people with obesity on weight reduction programs
Effect: caution advised for HP diets from animal sources in obesity
Certainty: Advice of the authors, not a measured risk of stones.
PLoS One, 2014 · checked 2026-10-07 · we read the abstract
ev-protks-03 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 6 RCTs
Our result showed that low protein with or without high fiber diet intervention does not decrease the recurrence of stone upon comparing with control groups (RR = 2.32, 95% CI = 0.42-12.85; P = 0.34) with significant heterogeneity among the studies (I2 = 81%, P = 0.02).
Who: patients with recurrent calcium stones
Effect: low protein +/- high fiber vs control: RR 2.32 (95% CI 0.42 to 12.85; P=0.34), I2=81%
Certainty: Very wide CI and heterogeneity; the conclusion is "does not help", not "harms".
PLoS One, 2021 · checked 2026-10-07 · we read the abstract
ev-protks-04 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 8 trials, 1855 participants
Content and results of multicomponent dietary interventions were heterogeneous; in one trial, fewer participants assigned increased dietary calcium, low animal protein, and low sodium had stone recurrence versus controls (20% vs 38%, p=0.03), while in another trial, more participants assigned diets that included low animal protein, high fruit and fiber, and low purine had recurrent stones than controls (30% vs 4%, p=0.004).
Who: adults with a history of nephrolithiasis
Effect: recurrence 20% vs 38% (p=0.03) with increased calcium + low animal protein + low sodium; 30% vs 4% (p=0.004) with low animal protein + high fruit and fiber + low purine
Certainty: Both results are from multicomponent diets; the effect of protein is not singled out.
Eur Urol, 2009 · checked 2026-10-07 · we read the abstract
ev-protks-05 · Meta-analysis or systematic review · Cochrane systematic review of RCTs · n = 5 studies, 379 adults
Long-term adherence (five years) to diets that feature normal levels of calcium, low protein and low salt may reduce numbers of stone recurrences, decrease oxaluria and calcium oxalate relative supersaturation indexes in people with idiopathic hypercalciuria who experience recurrent kidney stones.
Who: people with idiopathic hypercalciuria who experience recurrent kidney stones
Effect: fewer recurrences (RR 0.77, 95% CI 0.61 to 0.98, one 120 person trial); lower oxaluria
Certainty: Protein is one of three components; not assessed separately.
Cochrane Database Syst Rev, 2014 · checked 2026-10-07 · we read the abstract
ev-protks-06 · Observational data · systematic review and dose-response meta-analysis of cohorts · n = 14 prospective cohort studies
A positive association was observed between higher intake of nondairy animal protein (RR: 1.11; 95% CI: 1.03, 1.20; I2 = 0%, n = 4), total meat and meat products (RR: 1.22; 95% CI: 1.09, 1.38; I2 = 13%, n = 3), and processed meat (RR: 1.29; 95% CI: 1.10, 1.51; I2 = 0%, n = 2) with risk of kidney stones.
Who: general population, prospective cohorts
Effect: nondairy animal protein RR 1.11 (1.03-1.20); total meat RR 1.22 (1.09-1.38); processed meat RR 1.29 (1.10-1.51); dairy protein RR 0.91 (0.84-0.99); +100 g red meat RR 1.39 (1.13-1.71)
Certainty: NutriGrade: low confidence for most exposures; signs of publication bias.
Adv Nutr, 2022 · checked 2026-10-07 · we read the abstract
ev-protks-07 · Observational data · umbrella review (AMSTAR 2, NutriGrade) · n = 9 systematic reviews (6 with MA)
For none of the outcomes, evidence was found that HPI does specifically trigger kidney stones or diseases.
Who: systematic reviews of RCTs and cohorts on protein intake above 0.8 g/kg body weight per day
Effect: certainty 'possible' for no association between higher protein intake and stone risk
Certainty: The conclusion on stones rests on cohorts; level C.
Eur J Nutr, 2023 · checked 2026-10-07 · we read the abstract
ev-protks-08 · Observational data · umbrella review, results section · n = 4 cohort studies (one meta-analysis within the umbrella review)
Based on one SR with MA of cohort studies, a NutriGrade rating of ‘low’ was obtained for a 10% increase (RR: 1.1; 95% CI, 1.02–1.19) in the risk of incident stone formation with the exposition variable animal protein intake [20], while two other SRs (one without and one with MA) found the risk inconclusive [17] or found no effect of animal protein on the risk of incident stone formation [22].
Who: cohorts of adults, high vs low animal protein intake
Effect: RR 1.1 (95% CI 1.02 to 1.19); two other reviews inconclusive or null
Certainty: Opposite conclusions of other reviews; NutriGrade low.
Eur J Nutr, 2023 · checked 2026-10-07 · we read the fulltext
ev-protks-09 · Randomized controlled trial(s) · secondary analysis of a multicentre randomized controlled trial, 24 months · n = 307
Urinary calcium excretion increased at 3 (36.1%) and 12 (35.7%) months without changes in bone density or clinical presentations of new kidney stones.
Who: obese adults without serious medical illnesses, three US academic centers
Effect: urinary calcium +36.1% at 3 months, +35.7% at 12 months; no clinical presentations of new kidney stones
Certainty: Stones were not the primary endpoint; no imaging.
Clin J Am Soc Nephrol, 2012 · checked 2026-10-07 · we read the abstract
ev-protks-10 · Randomized controlled trial(s) · randomized controlled trial · n = 99
After adjustment for possible confounding effects of age, sex, education, and baseline protein and fluid intake, the relative risk of a recurrent stone in the intervention group was 5.6 (95% confidence interval 1.2-26.1) compared with the control group.
Who: persons with first calcium oxalate stones, Kaiser Permanente Northern California
Effect: recurrence 7.1 vs 1.2 per 100 person-years; adjusted RR 5.6 (95% CI 1.2 to 26.1)
Certainty: The intervention included bran (oxalate); few events (12 vs 2), wide CI.
Am J Epidemiol, 1996 · checked 2026-10-07 · we read the abstract
ev-protks-11 · Randomized controlled trial(s) · randomized controlled trial, 4 years · n = 175 randomized, 73 completed
Recurrence was 48% (11/23) in the LAPD group, 63% (17/27) in the HFD group and 48% (11/23) in the control group (p = not significant).
Who: idiopathic calcium stone formers; low animal protein diet <13% of energy from protein
Effect: recurrence 48% (11/23) low animal protein vs 48% (11/23) control; not significant
Certainty: Only 73 of 175 completed: a large loss to follow-up.
Nephron Clin Pract, 2008 · checked 2026-10-07 · we read the abstract
ev-protks-12 · Randomized controlled trial(s) · randomized controlled trial, 5 years · n = 120
However, urinary oxalate excretion increased in the men on the low-calcium diet (by an average of 5.4 mg per day [60 micromol per day]) but decreased in those on the normal-calcium, low-animal-protein, low-salt diet (by an average of 7.2 mg per day [80 micromol per day]).
Who: men with recurrent calcium oxalate stones and hypercalciuria
Effect: urinary oxalate -7.2 mg/day (normal Ca, low animal protein, low salt) vs +5.4 mg/day (low Ca)
Certainty: Effect of a combination; men only.
N Engl J Med, 2002 · checked 2026-10-07 · we read the abstract
ev-protks-13 · Observational data · systematic review of mixed designs · n = 20 articles on high protein diets
High protein diets increase urine calcium and uric acid and lower urine pH and citrate.
Who: studies of low carbohydrate, high protein, vegetarian and vegan diets
Effect: higher urine calcium and uric acid; lower urine pH and citrate
Certainty: Urinary risk factors, not stones; few direct studies.
Nutrients, 2021 · checked 2026-10-07 · we read the abstract
ev-protks-14 · Position of an expert body · society guideline based on a systematic search (CLU Working Group) · n = —
A low-normal protein intake decrease calciuria and could be useful in stone prevention and preservation of bone mass.
Who: hypercalciuric stone formers
Effect: low-normal protein intake advised
Certainty: Expert position.
Arch Ital Urol Androl, 2015 · checked 2026-10-07 · we read the abstract
ev-protks-15 · Position of an expert body · society guideline (CLU Working Group) · n = —
Despite the low level of scientific evidence, a low-protein (< 20 g/day) low-salt (< 2 g/day) diet with high hydration (> 3 liters/day) is strongly advised in children with cystinuria.
Who: children with cystinuria
Effect: protein <20 g/day, salt <2 g/day, fluids >3 L/day
Certainty: Rare group; low evidence, expert opinion.
Arch Ital Urol Androl, 2015 · checked 2026-10-07 · we read the abstract

How this page was made. Evidence was extracted from primary sources into cards, every number was re-checked against the source, and the text was written from those cards. Bioma Learn has no human medical reviewer at this time, and we say so rather than invent one. Methodology. This is information, not medical advice.

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