Which foods are highest in oxalate?

Spinach is the single highest common source (a half-cup cooked can exceed 700 mg). Other very-high foods include almonds, beets, rhubarb, Swiss chard, potatoes with skin, navy beans, soy, black tea, and dark chocolate in quantity. OxalWise organizes 300+ foods into low, moderate, high, and very-high bands per serving.

How much oxalate per day is recommended for kidney stone formers?

No urology guideline sets a numeric daily oxalate limit. The widely used figure — under 100 mg of dietary oxalate per day, with 50 mg for stricter cases — comes from the University of Chicago Kidney Stone Program. The right number is individual: a 24-hour urine test and your care team decide it.

Does boiling remove oxalate from food?

Yes, the soluble fraction — and only if you discard the water. Chai and Liebman (Journal of Agricultural and Food Chemistry, 2005) measured a 30-87% drop in soluble oxalate from boiling, 5-53% from steaming, and none from baking. The oxalate is not destroyed; it leaches out, and the study recovered essentially all of it in the cooking water. Boil, drain, and never reuse the water.

Should stone formers avoid calcium?

No — normal dietary calcium taken with meals binds oxalate in the gut so less is absorbed, and cutting calcium can raise stone risk. It is the most counterintuitive, best-replicated finding in stone prevention.

The questions every stone former asks

Do I have to give up spinach, almonds, and dark chocolate forever?

No — that is the entire point of the budget approach. A strict 50 mg day can still absorb a square of dark chocolate. What it cannot absorb is a daily spinach smoothie plus almonds plus beets. Frequency and portion, not prohibition. Most stone formers end up treating very-high foods as occasional guests rather than daily staples.

I eat a plant-based / vegan diet. Is this hopeless?

Harder, not hopeless. The workhorses of plant protein (beans, soy, nuts) run moderate-to-high, so the strategy shifts: lean on lentils and chickpeas over navy beans and soy, choose macadamias and pumpkin seeds over almonds and cashews, make kale and cabbage your default greens, boil-and-drain what you can, and be deliberate about calcium at every meal (fortified plant milks with calcium actually help the chaperone strategy). Many plant-based stone formers manage 50–100 mg days comfortably once the pattern clicks.

Is green tea really better than black tea?

In most published analyses, yes — brewed green tea typically carries a fraction of the oxalate of black tea, and herbal teas are essentially zero. The bigger variable is volume: two cups of black tea a day is a moderate habit; a daily pot is a major oxalate source. If you love black tea, keep the ritual and shrink the quantity.

What about coffee?

Drink your coffee. Brewed coffee is low in oxalate (~2 mg per cup), and large cohort studies have repeatedly found coffee drinkers form fewer stones, not more — likely a mix of fluid volume and other chemistry. It is one of the few pleasures a stone former does not have to negotiate.

Should I take a calcium supplement with meals instead of dairy?

Food calcium is the pattern with the best evidence. Calcium supplements have a mixed record — taken away from meals they do not bind meal oxalate and have been linked to higher stone risk in some studies. If you cannot do dairy, calcium-fortified plant milks taken with meals play the same chaperone role. Discuss supplements with your clinician before starting.

Why does the app say “don’t fear calcium”? My stone is made of calcium.

Because the calcium in your stone mostly came from your bones and your urine chemistry, not from the calcium on your plate — and cutting dietary calcium lets oxalate absorb more freely, which can raise stone risk. It is the single most counterintuitive finding in this field, and one of the best replicated. Normal calcium, taken with meals, is protective.

How accurate are these numbers, really?

Honest answer: within a band. Oxalate assays vary by lab method, and the food itself varies by variety, soil, season, and cooking. Published values for the same food can differ twofold. That is why OxalWise is organized around bands — the difference between 600 and 800 mg does not change any decision you will make. Where sources conflict, the food’s note says so.

Boiling really removes oxalate?

Yes — but only the soluble fraction, and only if you throw the water away. Chai and Liebman (Journal of Agricultural and Food Chemistry, 2005) measured a 30–87% drop in soluble oxalate from boiling, against 5–53% for steaming and none for baking. The oxalate is not destroyed; it leaches out, and the study recovered essentially all of it in the cooking water. So if the liquid goes into the soup, the risotto, or the gravy, you have removed nothing. The range is wide and food-specific — treat it as a reason to boil and drain, not as a fixed discount you can apply to a number.

Is a low-oxalate diet safe for everyone?

It is unnecessary for most people who have never formed stones, and over-restriction can shrink a healthy diet. It is designed for calcium-oxalate stone formers, people with high urinary oxalate, and people with fat-malabsorption conditions (post-bariatric, Crohn’s, celiac). If you are unsure which you are, a 24-hour urine test answers it — ask your clinician.

What is enteric hyperoxaluria?

When fat is not absorbed properly (bariatric surgery, Crohn’s, celiac, pancreatic insufficiency), it binds calcium in the gut — leaving oxalate unchaperoned and hyper-absorbable. Urinary oxalate can climb dramatically. The diet strategy intensifies (lower oxalate, calcium with meals, sometimes bile-acid-directed care), and it should be managed with a specialist.

Does vitamin C turn into oxalate?

Yes, a portion of it. In a controlled study (Traxer et al., Journal of Urology, 2003), 2 g a day of ascorbic acid raised urinary oxalate by 33% in stone formers. In the Health Professionals Follow-up Study, men taking 1,000 mg or more a day had a modestly higher stone risk; the same association was not found in women (Ferraro et al., American Journal of Kidney Diseases, 2016). Food sources of vitamin C were not linked to higher risk in either — this is a supplement question, not a fruit question.

Turmeric supplements — yes or no?

Culinary turmeric (the amounts in curries) is a few milligrams of oxalate — fine. Concentrated curcumin supplements are a much larger, poorly characterized exposure, and some clinicians specifically flag them for stone formers. The spice rack is safe; the supplement aisle is where to be cautious.

How fast does diet change urinary oxalate?

Within days to a couple of weeks — urinary oxalate responds quickly to intake. But stone risk is a long game measured in months and years of urine chemistry, which is why the sustainable budget beats the heroic two-week ban every time.

How much does OxalWise cost?

The website is free. The iOS app includes the full Food Atlas and Science guide free, plus ten tracker logs to try the habit; a single one-time purchase unlocks unlimited tracking. No subscription, no account, no ads — and your data never leaves your device.

Is OxalWise medical advice?

No. It is an educational reference and a self-tracking tool. It does not diagnose, treat, or replace your clinician. Kidney disease, pregnancy, primary hyperoxaluria, and enteric hyperoxaluria all change the rules — if any apply, build your plan with your physician or a registered dietitian.