Spinach is one of the highest-oxalate foods you can eat. Raw spinach contains roughly 1,145 mg of total oxalates per 100 grams, with about 800 mg of that in soluble form, the type your body can absorb. For context, people following a low-oxalate diet are typically advised to stay under 100 mg per day. A single serving of raw spinach can blow past that limit several times over.
How Spinach Compares to Other Greens
Not all leafy greens carry the same oxalate load. Spinach sits at the extreme end of the scale. At around 1,145 mg per 100 grams, it dwarfs most other vegetables. Arugula, by comparison, contains just 7 mg per 100 grams. Lettuce, bok choy, and most varieties of cabbage are also considered low-oxalate. Kale falls in the low-to-moderate range, making it a practical substitute if you’re trying to cut back on oxalates while still eating nutrient-dense greens.
Other foods that land in the “very high” category alongside spinach include amaranth, rhubarb, beet greens, and Swiss chard. But even among these, spinach consistently tops the list in most analyses. One earlier study measured spinach at 330 mg of total oxalate per 100 grams of fresh weight, which is lower than the 1,145 mg figure from a more detailed analysis. The difference likely reflects the variety of spinach, growing conditions, and how oxalates were measured. Either way, spinach is firmly in the highest tier.
Why Oxalates Matter for Kidney Stones
About 80% of kidney stones are made of calcium oxalate, which is why oxalate intake gets so much attention. Here’s how it works: when you eat oxalate-rich foods alongside calcium-rich foods, the oxalate and calcium bind together in your gut and leave your body in your stool. That’s the ideal scenario. The oxalate never reaches your kidneys.
Problems arise when there isn’t enough calcium in the gut to pair with the oxalate. The unbound oxalate gets absorbed into your bloodstream, filtered by your kidneys, and ends up in your urine. Once there, it can combine with calcium in the urinary tract and crystallize into a stone. This is why Johns Hopkins Medicine actually recommends that calcium oxalate stone formers eat adequate dietary calcium. Cutting calcium makes things worse by freeing up more oxalate for absorption.
If you’ve never had a kidney stone and have no risk factors, the oxalates in spinach are unlikely to cause problems on their own. But if you eat large amounts of spinach regularly, especially without much calcium in the same meal, you’re giving your body a lot of oxalate to handle.
Cooking Reduces Oxalates Significantly
If you love spinach but want to lower your oxalate exposure, how you prepare it makes a real difference. Boiling is the most effective method. Research published in the Journal of Agricultural and Food Chemistry found that boiling spinach reduced its soluble oxalate content by 87%, dropping it from about 803 mg to just 107 mg per 100 grams. The key is that soluble oxalates leach into the cooking water, so discarding the water removes most of them.
Steaming is less effective but still helpful, cutting soluble oxalates by roughly 42%, from 803 mg down to 468 mg. That’s about half the reduction you’d get from boiling. Insoluble oxalates, which are already bound to minerals and less readily absorbed, stayed roughly the same regardless of cooking method.
A few practical takeaways from this:
- Boiling and draining is the single best way to lower oxalates in spinach. Don’t reuse the cooking water for soups or sauces if oxalates are a concern.
- Steaming helps, but leaves more than half the soluble oxalate intact.
- Raw spinach in smoothies and salads delivers the full oxalate load. If you’re eating spinach daily in smoothie form, you’re getting the maximum amount.
How Much Is Too Much?
Clinical guidelines for people with a history of calcium oxalate kidney stones generally set the target at around 100 mg of oxalate per day. That’s a tight budget. Even a small 50-gram portion of raw spinach could contain over 400 mg of soluble oxalate, four times the daily limit in a single handful.
For people without kidney stone history, there’s no universally agreed-upon daily limit. Most healthy kidneys can handle moderate oxalate intake without issues, especially when meals include enough calcium and fluids. The concern grows with consistently high intake, low calcium diets, certain gut conditions that increase oxalate absorption (like inflammatory bowel disease or a history of gastric bypass), or a family history of stones.
Lower-Oxalate Swaps
You don’t have to give up greens to reduce oxalate intake. Several alternatives deliver similar vitamins and minerals without the extreme oxalate content. Arugula contains just 1 mg of oxalate per typical one-cup serving. Romaine lettuce, watercress, and bok choy are also low-oxalate options. Kale provides a comparable nutrient profile to spinach, with high levels of vitamins A, C, and K, while carrying far less oxalate.
If you still want spinach in your diet, rotating it with these lower-oxalate greens reduces your overall exposure. Pairing spinach with calcium-rich foods like yogurt, cheese, or fortified plant milks also helps bind the oxalate in your gut before it can be absorbed. And choosing boiled spinach over raw cuts the soluble oxalate by nearly 90%, making an occasional serving much more manageable even on a restricted diet.