How the grades work

Each food's grade is the middle of its published oxalate measurements, converted to one normal serving and compared with 50 mg, the daily amount many kidney stone clinics aim for.

The grade scale

• A Very low, under 5 mg per serving
• B Low, 5 to 10 mg per serving
• C Moderate, 10 to 25 mg per serving
• D High, 25 to 50 mg per serving
• E Very high, over 50 mg per serving

A is under 10% of a 50 mg day. E is more than a whole day in one serving. No published per-serving scale exists, so these bands are ours, anchored to the 50 mg day.

Why a range, and why the middle

Studies disagree on oxalate more than on most nutrients. Raw spinach reads 330 to 1,370 mg per 100 g across the studies here, because cultivar, season, soil, cooking and lab method all move the number. So every food page shows each study's value as a dot on one bar, and the grade uses the middle value. The highest value would grade broccoli and cauliflower as high-oxalate on the strength of one study each, which disagrees with every clinical list we checked.

Which studies count

• Studies that set out to measure oxalate in foods, by HPLC, enzymatic or comparable methods. Papers that test a new lab reagent on a few vegetables are left out, since they report values like 1,431 mg soluble oxalate per 100 g of beetroot, far outside every food survey.
• Values per fresh or cooked weight. Values per dried weight are left out unless the food is eaten dried, like raisins or lentils.
• Rows that report only soluble oxalate show on the food page but don't set the grade, since soluble oxalate understates the total.
• When the serving is a cooked one, like beans, the grade uses the cooked measurements.

Most produce values come from Table 5 of a 2023 review, "Oxalate in Foods", in Foods 12(17):3201, published under CC BY 4.0. Each value still credits the original study. Nuts, grains, drinks, chocolate and animal foods come from the original papers, read at the source.

The Harvard T.H. Chan School of Public Health Oxalate Table (2023) gives one value per household serving, like half a cup. Values the table marks as directly measured, mostly in John Knight's lab at the University of Alabama at Birmingham, can be a food's only source, and the food page then says one study. Values it estimates count only next to another source. Each serving is converted to grams at a standard household weight, which the food page states row by row. Where a paper gives only a range, we enter the top of it.

Swaps and dishes

Each swap is picked by hand from foods used the same way, like oat milk for almond milk or winter squash for sweet potato, and shows only when it grades lower. Dishes are typical home recipes for one serving. Each ingredient uses the middle value from its own food page, scaled to the amount in the dish, and anything with no published value here, like cooking oil, is listed as not counted.

Two kinds of value are left out until they can be checked: figures from review tables that name no original measurement, and a single study's sesame value of 3,800 mg per 100 g, about 10 times every other nut.

What a grade doesn't tell you

A low-oxalate diet helps calcium oxalate stone formers with high urine oxalate. It doesn't help every stone type, and cutting calcium backfires. A 24-hour urine test tells you which applies to you. Calcium eaten in the same meal binds oxalate in the gut, so pairing a high-oxalate food with dairy lowers what reaches your urine.

All 23 sources

1. Akhtar M.S., Israr B., Bhatty N., Ali A. Effect of Cooking on Soluble and Insoluble Oxalate Contents in Selected Pakistani Vegetables and Beans. Int. J. Food Prop. 2011;14:241–249. doi.org/10.1080/10942910903326056
2. Arias-Rico J., Macías-León F.J., Alanís-García E., Cruz-Cansino N.d.S., Jaramillo-Morales O.A., Barrera-Gálvez R., Ramírez-Moreno E. Study of Edible Plants: Effects of Boiling on Nutritional, Antioxidant, and Physicochemical Properties. Foods. 2020;9:599. doi.org/10.3390/foods9050599
3. Borin JF, Knight J, Holmes RP, Joshi S, Goldfarb DS, Loeb S. Plant-Based Milk Alternatives and Risk Factors for Kidney Stones and Chronic Kidney Disease. J Ren Nutr 32(3):363-365. 2022. doi.org/10.1053/j.jrn.2021.03.011
4. Charrier MJ, Savage GP, Vanhanen L. Oxalate content and calcium binding capacity of tea and herbal teas. Asia Pac J Clin Nutr 11(4):298-301. 2002. doi.org/10.1046/j.1440-6047.2002.00294.x
5. Harvard T.H. Chan School of Public Health, Department of Nutrition (values largely measured in the lab of John Knight, UAB). Oxalate Table (posted Nov 2023). Nutrition Questionnaire Service Center file download. 2023. hsph.harvard.edu/wp-content/uploads/2024/07/OXALATE-TABLE-1.xlsx
6. Honow R, Gu KL, Hesse A, Siener R. Oxalate content of green tea of different origin, quality, preparation and time of harvest. Urol Res 38(5):377-381. 2010. doi.org/10.1007/s00240-009-0245-x
7. Hönow R., Hesse A. Comparison of Extraction Methods for the Determination of Soluble and Total Oxalate in Foods by HPLC-Enzyme-Reactor. Food Chem. 2002;78:511–521. doi.org/10.1016/S0308-8146(02)00212-1
8. Judprasong K, Charoenkiatkul S, Sungpuag P, Vasanachitt K, Nakjamanong Y. Total and soluble oxalate contents in Thai vegetables, cereal grains and legume seeds and their changes after cooking. J Food Compos Anal 19:340-347. 2006. doi.org/10.1016/j.jfca.2005.04.002
9. Judprasong K., Charoenkiatkul S., Sungpuag P., Vasanachitt K., Nakjamanong Y. Total and Soluble Oxalate Contents in Thai Vegetables, Cereal Grains and Legume Seeds and Their Changes after Cooking. J. Food Compos. Anal. 2006;19:340–347. doi.org/10.1016/j.jfca.2005.04.002
10. Kim D.-J., Kim H., Kim M., Lee J. Analysis of Oxalic Acid of Various Vegetables Consumed in Korea. Food Sci. Biotechnol. 2007;16:650–654. [ Google Scholar ]
11. Libert B.O. Rapid Determination of Oxalic Acid by Reversed-Phase High-Performance Liquid Chromatography. J. Chromatogr. 1981;210:540–543. doi.org/10.1016/S0021-9673(00)80349-0
12. Liebman M, Okombo J. Oxalate content of selected pasta products. J Food Compos Anal 22:254-256. 2009. doi.org/10.1016/j.jfca.2008.10.013
13. Mahdavi R, Lotfi Yagin N, Liebman M, Nikniaz Z. Effect of different brewing times on soluble oxalate content of loose-packed black teas and tea bags. Urolithiasis 41(1):15-19. 2013. doi.org/10.1007/s00240-012-0521-z
14. Ritter MMC, Savage GP. Soluble and insoluble oxalate content of nuts. J Food Compos Anal 20(3-4):169-174. 2007. doi.org/10.1016/j.jfca.2006.12.001
15. Santamaria P., Elia A., Serio F., Todaro E. A Survey of Nitrate and Oxalate Content in Fresh Vegetables. J. Sci. Food Agric. 1999;79:1882–1888. doi.org/10.1002/(SICI)1097-0010(199910)79:13<1882::AID-JSFA450>3.0.CO;2-D
16. Savage G.P., Mårtensson L. Comparison of the Estimates of the Oxalate Content of Taro Leaves and Corms and a Selection of Indian Vegetables Following Hot Water, Hot Acid and in Vitro Extraction Methods. J. Food Compos. Anal. 2010;23:113–117. doi.org/10.1016/j.jfca.2009.07.001
17. Savage G.P., Vanhanen L., Mason S.M., Ross A.B. Effect of Cooking on the Soluble and Insoluble Oxalate Content of Some New Zealand Foods. J. Food Compos. Anal. 2000;13:201–206. doi.org/10.1006/jfca.2000.0879
18. Schroder T, Vanhanen L, Savage GP. Oxalate content in commercially produced cocoa and dark chocolate. J Food Compos Anal 24:916-922. 2011. doi.org/10.1016/j.jfca.2011.03.008
19. Siener R, Honow R, Voss S, Seidler A, Hesse A. Oxalate content of cereals and cereal products. J Agric Food Chem 54(8):3008-3011. 2006. doi.org/10.1021/jf052776v
20. Siener R, Seidler A, Voss S, Hesse A. Oxalate content of beverages. J Food Compos Anal 63:184-188. 2017. doi.org/10.1016/j.jfca.2017.08.005
21. Siener R. Nutrition and Kidney Stone Disease. Nutrients 13(6):1917. 2021. doi.org/10.3390/nu13061917
22. Siener R., Seidler A., Hönow R. Oxalate-Rich Foods. Food Sci. Technol. 2021;41:169–173. doi.org/10.1590/fst.10620
23. Wilson C.W., Shaw P.E., Knight R.J. Analysis of Oxalic Acid in Carambola (Averrhoa Carambola L.) and Spinach by High-Performance Liquid Chromatography. J. Agric. Food Chem. 1982;30:1106–1108. doi.org/10.1021/jf00114a025

By Oliver Silen · Updated November 2, 2026