Kidney Stone Symptoms and Prevention, and Cautions While Dieting

Urinary stones are one of the conditions that suddenly cause such severe flank pain that people end up in the emergency room. More people report going to the ER for a urinary stone as summer draws to a close; according to National Health Insurance Service data, August is the month with the most urinary stone patients, and 317,472 people were treated for this condition in 2022 alone. If the urine remains in a state prone to forming stones, the same thing happens again within a few years, so management after the pain passes is as important as treatment.

A urinary stone is a stone that forms along the path urine takes out of the body: the kidney, ureter, bladder and urethra. It is not a substance that came in from outside; calcium, oxalic acid and uric acid dissolved in the urine clump into crystals and grow. About 80% of adult stones contain calcium, and among those, calcium oxalate stones are more common than calcium phosphate stones, while the rest are uric acid stones or infection-related stones. Citrate in the urine binds to calcium first and prevents crystals from clumping; when citrate decreases, crystals form more easily even with the same amount of calcium. In the 2022 National Health Insurance Service data, men accounted for 66.2% of those treated, twice the share of women, and people in their 50s were the largest group at 23.5%.

The most prominent sign that makes you suspect a urinary stone is extreme pain that hits one flank without warning. It does not settle easily even with painkillers and comes in waves, and when the stone moves down it can radiate to the lower abdomen and groin. When the stone scrapes the ureter wall, blood appears in the urine, sometimes visible to the naked eye and sometimes found only on microscopic examination. Nausea and vomiting can accompany the pain, and when the stone comes down near the bladder, urinary frequency and a feeling of incomplete emptying can occur.

However, a stone alone rarely causes a fever, so if flank pain comes with chills or a high fever, a urinary tract infection is likely and emergency care is needed. You should also see a doctor right away if vomiting is so severe that you cannot keep even water down, if the amount of urine suddenly decreases, or if the urine turns red or brown.

In its 2025 guideline, the European Association of Urology (EAU) presents recurrence prevention standards that apply regardless of stone type, together with their grades.

Because many stones are made of calcium, quite a few people try to cut calcium first, but the guideline recommends the opposite: maintain 1-1.2 g per day. This is because calcium you eat binds with oxalate in the gut first and leaves the body together in the stool; when calcium is reduced, oxalate that has lost its partner is absorbed as is and actually raises the urinary oxalate concentration. In a 5-year randomized controlled study in the New England Journal of Medicine as well, among 120 patients with recurrent calcium stones, the 5-year recurrence rate on a low-calcium diet restricted to 400 mg of calcium was 38%, while on a diet that kept calcium at 1,200 mg and restricted only salt and animal protein, the recurrence rate was lower, at 20%. However, because this study involved men with recurrent stones and high urinary calcium, its range of application may vary depending on stone composition and kidney function.

Fluid intake is the item every guideline puts first, but the PUSH trial published in The Lancet in March 2026 tested it separately. Among 1,658 participants with a stone history and low urine volume, one group received a two-year behavioral program that used personalized fluid prescriptions, health coaching, text reminders, a Bluetooth water bottle and even financial incentives. Urine volume in the intervention group did increase, but symptomatic stone recurrence did not differ: 19% in the intervention group versus 20% in the control group (hazard ratio 0.96). This is more accurately read not as meaning that you need not drink water, but that salt, protein intake and body weight must also be addressed in order to reduce recurrence.

A 2025 systematic review (15 studies over 30 years, 97,645 participants) concluded that there is an association between high body mass index and stone formation, but individual study results were mixed. Diet plans easily end up containing items that conflict with stone-management standards, and the following four overlap most often in practice.

First, low-carb high-fat and ketogenic diets increase uric acid stones. In a meta-analysis that followed 2,795 people in 36 studies of ketogenic diets for an average of 3.7 years, the stone incidence was 5.9% (7.9% in adults only), and 48.7% of the stones that formed were uric acid stones. Compared with calcium stones making up 80% in the general population, the composition is inverted; this is because drastically cutting carbohydrates pushes urine toward acidity, making uric acid more likely to clump into crystals.

Second, oxalate is concentrated in diet foods. According to the Harvard School of Public Health content table, half a cup of boiled spinach contains about 547 mg, 28 g of almonds about 72 mg, and half a cup of sweet potato about 54 mg, so on a low-carb diet that combines these ingredients, oxalate intake can even increase compared with before dieting. Because the EAU guideline recommends oxalate restriction only at a weak grade, it is more realistic not to eat them all in one meal and to eat them with calcium-containing dairy so that they bind in the gut beforehand.

Third, high-dose vitamin C supplements are worth rechecking. In a 2026 analysis in the Journal of Endourology that pooled 9 studies, 24-hour urinary oxalate excretion in the group taking vitamin C supplements was measured at an average of 6.45 mg per day higher than in the placebo group. Ordinary intake amounts are not a problem, but if you have a stone history, it is worth checking whether you take high-dose single-ingredient products.

Fourth, fluids must be replenished to match what is lost. If the fluid lost through exercise and saunas increases while the amount you drink stays the same, then together with a low-carb diet the conditions are created for urine to become concentrated and acidic. If your urine is a dark yellow color, you are running short, so on days you sweat a lot, drink that much more.

Once you have a urinary stone, you often get one again, but changing the conditions of your urine can lower that possibility considerably. Rather than relying only on drinking more water, check salt, protein and calcium intake together, and if you are dieting, also look at uric acid stones from ketogenic diets, an over-reliance on oxalate-rich foods, and high-dose vitamin C.

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• European Association of Urology (EAU), Guidelines on Urolithiasis (2025)
• Borghi L, et al. New England Journal of Medicine (2002)
• Desai AC, et al. PUSH trial, The Lancet (2026)
• Farkouh A, et al. Journal of Endourology (2026)
• Acharya P, et al. Diseases (2021), meta-analysis of stones on ketogenic diets
• National Health Insurance Service press release on urinary stone treatment status (2023)
• Harvard T.H. Chan School of Public Health, Oxalate Content of Foods

The research results cited are values observed in the participants of those studies; if you have symptoms, please see a nearby medical institution.

Reviewed by: Dr. Park Ji-seon · Director, ACRO Korean Medicine Clinic · Last reviewed 2026-09-20

This article is intended for general informational purposes, and results may vary depending on individual eating habits and constitution. Please confirm the exact direction for diet and weight management through consultation with a professional.