After a kidney stone, the most useful question is not "what did I eat?" — it is "what is my urine chemistry doing?" That question is answered by a 24-hour urine test, the tool that measures how much stone-forming material the kidneys actually put out in a day. It is the difference between guessing at prevention and measuring it.
A standard 24-hour urine stone profile reports urine volume, pH, and the excretion of calcium, oxalate, citrate, uric acid, sodium, potassium, magnesium, and creatinine (creatinine is the check that the collection was complete). From these, the laboratory calculates relative supersaturation for calcium oxalate, calcium phosphate, and uric acid — the odds that those salts can stay dissolved. High calcium, oxalate, and sodium push risk up; high volume, citrate, potassium, and magnesium push it down.
Timing matters as much as content. The collection should happen on a usual diet — not right after the acute episode, not during a crash diet. Guidelines suggest waiting at least three weeks to three months after an acute stone event, and then repeating the test 8 to 12 weeks after starting any dietary or medication change to see if the target moved. Once values stabilize, an annual check keeps the pattern honest.
Each urinary risk factor has a food counterpart, and the oxalate side is the one this database measures directly:
| Food | Oxalate (mg) | Serving | Rating |
|---|---|---|---|
| Spinach, raw | 590 mg | 1 serving | Avoid |
| Almonds | 107 mg | 1/4 cup | Avoid |
| Beets, boiled | 48 mg | 1/2 cup | Caution |
| Yogurt, plain whole-milk | 5 mg | 6 oz | Safe |
| Banana | 6 mg | 1 medium | Safe |
High urine oxalate traces to the top rows — spinach, almonds, beets. High urine calcium is influenced less by dietary calcium (which usually binds oxalate in the gut) and more by sodium, which pulls calcium into the urine. That is why the sodium row of a 24-hour report matters even though sodium is not a stone ingredient itself. Yogurt and banana are the low-oxalate end that also support the protective side of the profile.
If you have had a stone, ask your doctor whether a 24-hour urine workup makes sense — most recurrent stone formers and many first-timers qualify. Do the collections on a normal diet, follow the kit instructions exactly, and do not "eat clean" to impress the test; the whole point is a true sample. The result turns prevention from generic advice ("drink water") into a specific plan ("your oxalate is the issue; here is the target"), which is the entire purpose of the test.
See how oxalate values are measured and verified on our data methodology page.