“Oxalates make spinach unhealthy.”
Spinach is not unhealthy because of its oxalates; for most people it is a nutritious vegetable.
You do not need to avoid spinach because of its oxalates. If you have had calcium-oxalate kidney stones, follow advice made for your stone type, which may include limiting spinach, rather than a rule meant for everyone.
Keep spinach in your meals if you enjoy it. If you have had a kidney stone, ask your doctor which type it was before you change your diet.
Safety note: Very large amounts of oxalate-rich greens, such as a juice cleanse, have caused rare cases of serious kidney injury, mostly in people with kidney disease, past gastric bypass surgery or a recent long course of antibiotics. If you take warfarin, keep the amount of spinach and other vitamin K-rich greens you eat steady instead of making sudden changes.
Talk to a healthcare professional if: you have had a kidney stone, to learn the stone type and get a prevention plan, or you have kidney disease or past weight-loss surgery and are thinking about a juice cleanse.
Large studies that followed about 240,000 adults found that oxalate in food, most of it from spinach, was not a major risk factor for kidney stones, and spinach is a good source of vitamin K. The small grain of truth is that men and older women who ate spinach most often had somewhat more kidney stones. Confidence is moderate because the long-term evidence comes from observational studies that relied on food questionnaires.
Spinach is not unhealthy because of its oxalates; for most people it is a nutritious vegetable. Oxalate from food does raise oxalate in urine, which matters mainly for people who form calcium-oxalate kidney stones, and getting enough calcium in the diet lowers how much oxalate is absorbed.
In a controlled feeding study, the oxalate people ate made up about a quarter to half of the oxalate in their urine, more than once thought, and cutting the calcium in the diet raised urine oxalate by about 28 percent. In three large US studies following about 240,000 adults, spinach supplied more than 40 percent of the oxalate people ate. Men and older women who ate spinach 8 or more times a month had about 30 percent more kidney stones than those who ate it less than once a month, younger women showed no link, and the researchers concluded that oxalate in food is not a major risk factor for kidney stones.
If you form calcium-oxalate stones, do not cut back on calcium on your own: in the right amounts, calcium in food helps block oxalate in the gut. US kidney guidance lists spinach, rhubarb, nuts, peanuts and wheat bran as high-oxalate foods that people with calcium-oxalate stones may want to avoid, alongside eating less sodium.
Can spinach add useful nutrients to your diet?
Yes. Spinach is one of the green leafy vegetables that supply vitamin K, which the body needs to make the proteins that help blood clot.
- Taylor EN, Curhan GC. Oxalate intake and the risk for nephrolithiasis. Journal of the American Society of Nephrology. 2007;18(7):2198-2204. DOI: 10.1681/ASN.2007020219. PMID: 17538185
- Holmes RP, Goodman HO, Assimos DG. Contribution of dietary oxalate to urinary oxalate excretion. Kidney International. 2001;59(1):270-276. DOI: 10.1046/j.1523-1755.2001.00488.x. PMID: 11135080
- National Institute of Diabetes and Digestive and Kidney Diseases. Eating, Diet, & Nutrition for Kidney Stones. Last reviewed May 2017
- Makkapati S, D'Agati VD, Balsam L. "Green Smoothie Cleanse" Causing Acute Oxalate Nephropathy. American Journal of Kidney Diseases. 2018;71(2):281-286. DOI: 10.1053/j.ajkd.2017.08.002. PMID: 29203127
- MedlinePlus (US National Library of Medicine). Vitamin K. Review date 1/21/2025