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Cola, Phosphoric Acid, and Kidney Stones: The Trial, the Reversal, and the Guideline
Few dietary questions in stone medicine have a plot twist as clean as the cola story: a randomized trial that seemed to settle the case, a giant cohort that refused to confirm it, and a practice guideline that split the difference by naming the ingredient that matters — phosphoric acid.
The finding, plainly: Shuster and colleagues (Journal of Clinical Epidemiology, 1992) randomized 1,009 men who drank at least half a liter of soft drinks daily to either continue or abstain for three years. Abstainers formed 6.4 percent fewer stones — and the effect concentrated in the colas: men who dropped phosphoric-acidified sodas had about a 15 percent lower recurrence rate, while citric-acid sodas showed no such effect. Then Curhan's 1996 cohort of 45,289 men complicated the story: cola intake showed no association with stone formation when overall diet was held constant. Ferraro's 2013 analysis of three US cohorts sharpened it again: sugar-sweetened soda carried a higher stone risk — the fructose pathway — while artificially sweetened and noncola versions were weaker or neutral. Saldana's case-control work added the kidney-disease angle: two or more colas a day associated with chronic kidney disease risk, and noncola carbonated drinks showed no association.
The Ingredient Is the Story, Not the Bubbles
Cola is acidified with phosphoric acid; most clear and fruit-flavored sodas use citric acid. The distinction matters because the two acids do different things in urine chemistry: phosphoric acid loads the urine with phosphate and tends to lower urinary pH — conditions that favor stone formation — while citrate is a known stone inhibitor that the kidney excretes when you consume citric acid. The American College of Physicians' 2014 guideline on recurrent stones put this into practice language: evidence showed patients who reduced soda acidified with phosphoric acid had fewer recurrences, and clinicians were encouraged to steer patients away from colas rather than fruit-flavored sodas.
The honest reading across the studies: the strongest signal attaches to phosphoric-acid cola and to sugar-sweetened soda (which brings fructose into the picture), the volume of fluid matters at least as much as the type, and no study shows that occasional clear soda is a stone hazard. Carbonation itself has never been convincingly implicated — the bubble is not the problem.
The boundary, stated clearly: these are observational associations plus one modest randomized trial; none of them establishes that your daily cola caused your stone, and none licenses the claim that quitting it guarantees prevention. People with diabetes, kidney disease, or heavy soda habits have bigger levers — overall fluid volume, sodium, and the plate — and their clinicians know which apply.
What the Drink Table Looks Like
| Food | Oxalate (mg) | Serving | Rating |
|---|
| Water, still | 0 mg | 1 glass | Safe |
| Water with lemon | 0 mg | 1 glass | Safe |
| Milk, plain | low | 1 glass | Safe |
| Cola (phosphoric acid) | 0 mg oxalate; sugared versions add fructose load | 12 oz can | Caution |
| Clear soda (citric acid) | 0 mg oxalate; citrate-bearing acid | 12 oz can | Caution |
The oxalate column is zeros across the board — soda is not an oxalate problem. The caution ratings reflect what else rides along: fructose load in sugared versions, phosphoric acid in colas, and the displacement problem, in which a can of anything is a glass of water you did not drink. Citrate-bearing clear sodas are not a stone therapy, but they are also not the cola.
What to Do With This
The practical hierarchy: water first, with lemon if citrus appeal helps the volume habit. If a soda habit is the sticking point, swapping phosphoric cola for a citric-acid version or — better — shrinking the can while growing the water is the move with trial data behind it. And if the 24-hour urine shows low citrate or low volume, the beverage log is the first thing your clinician will ask to see.
Frequently Asked Questions
Does cola cause kidney stones?
The evidence is mixed and ingredient-specific. One randomized trial found abstaining from phosphoric-acid soda cut recurrences about 15 percent; a large cohort found no cola effect once diet was held constant; sugared soda shows the most consistent signal across cohorts. No study proves causation for an individual.
Is sparkling water a problem too?
Carbonation itself has not been linked to stones — the concern in cola is phosphoric acid and, in sugared drinks, fructose. Plain sparkling water delivers fluid volume with neither, which is the column that matters most.
See how oxalate values are measured and verified on our data methodology page.
Medical Disclaimer: This site is a dietary reference tool based on published food composition data. It does not provide medical advice, diagnose, or treat any condition. Talk to your doctor or a registered dietitian before changing your diet, especially if you have kidney stones, kidney disease, or other medical conditions.