Vegetables and oxalates: 61 foods rated

Beetroot is high in oxalate, and boiling is the lever that works: measured across vegetables, boiling removes 30 to 87 per cent of the soluble oxalate against 5 to 53 per cent for steaming, and the loss turns up in the water. So boil it and pour the water away - which is the opposite of how beetroot is usually roasted.

• Chai W & Liebman M, J Agric Food Chem 53 (2005), 3027-3030, which measured 30-87 % loss of soluble oxalate on boiling against 5-53 % on steaming
• Noonan SC & Savage GP, Asia Pac J Clin Nutr 8 (1999)

Potato sits high here largely because of the skin: the oxalate is concentrated in it and just under it, so a jacket potato eaten whole and a peeled boiled one are not the same food on this axis. Boiling and pouring the water away is the lever that works, since the soluble fraction leaves with it, and peeling first removes most of what would have leached anyway. Cultivar does change the content, but no published measurement ranks red potatoes against white, and skin colour is not a reliable guide to cultivar.

• Chai W & Liebman M, J Agric Food Chem 53 (2005), 3027-3030
• Noonan SC & Savage GP, Asia Pac J Clin Nutr 8 (1999)

Spinach is the highest-oxalate leaf in ordinary use, and it has been measured directly against kale for exactly this reason: kale's iron is absorbed and spinach's is not, because spinach's own oxalate locks it up. The same binding works for you at the table - spinach with cheese or yoghurt is a different exposure from spinach alone. Boiling and draining removes a real share; wilting in the pan removes none. Jaeger is the mechanism behind that: only the SOLUBLE form of oxalate can be absorbed, and how much is soluble depends on pH and on the calcium and magnesium present — which is why calcium eaten in the same meal lowers what reaches the blood. It is a review and a model, publishing no oxalate figure for any food, and it says nothing about the oxalate the body makes itself. How much of this reaches the urine was measured rather than assumed: on controlled diets, dietary oxalate accounted for 24 to 42 per cent of urinary oxalate — well above the 10 to 20 per cent believed before — and cutting the calcium of a 250 mg oxalate diet from 1,002 to 391 mg raised urinary oxalate by 28 per cent, taking the dietary share to 53. The calcium eaten alongside is most of the answer.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8 (1999) 64–74: mean oxalate intake 70–150 mg a day in English diets, tea the largest single contributor, and soaking or cooking reduces oxalate by leaching
• Jaeger Ph. et al., Nephron Physiol 98 (2004) 64-71, dietary intake and intestinal absorption of oxalate
• Holmes R.P. et al., Kidney Int 59 (2001) 270-276, contribution of dietary oxalate to urinary oxalate

Sweet potato holds its oxalate throughout the flesh rather than in the skin, so peeling does little. Boiling and draining is what works, and it is exactly what nobody does with a sweet potato - baking and roasting keep every milligram.

• Chai W & Liebman M, J Agric Food Chem 53 (2005), 3027-3030, which measured 30-87 % loss of soluble oxalate on boiling against 5-53 % on steaming
• Noonan SC & Savage GP, Asia Pac J Clin Nutr 8 (1999)

Taro carries its oxalate as needle-shaped crystals called raphides, and they are why raw taro makes the mouth and hands itch. Thorough cooking is not optional here - it is what makes the corm edible at all, and it lowers the oxalate at the same time.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Cassava is moderate here, and it is the one vegetable on this list where the processing is not optional: it must be soaked, fermented or boiled to remove its cyanogenic compounds, and every one of those steps also takes soluble oxalate away. Safety and this axis pull the same way.

• Chai W & Liebman M, J Agric Food Chem 53 (2005), 3027-3030, which measured 30-87 % loss of soluble oxalate on boiling against 5-53 % on steaming
• Noonan SC & Savage GP, Asia Pac J Clin Nutr 8 (1999)

Rocket is a moderate-oxalate leafy green — lower than spinach but still a source in large raw amounts. Rotating it with low-oxalate greens keeps oxalate intake down.

Yam is moderate rather than high, and it is nearly always boiled - in West African cooking it is boiled and pounded, which is the single best preparation for oxalate because the water is discarded and the pounding uses none of it.

• Chai W & Liebman M, J Agric Food Chem 53 (2005), 3027-3030, which measured 30-87 % loss of soluble oxalate on boiling against 5-53 % on steaming
• Noonan SC & Savage GP, Asia Pac J Clin Nutr 8 (1999)

Artichoke is a thistle, and thistles are the family you would expect to be high - but the part eaten is the flower base and the fleshy leaf ends, not the foliage where oxalate concentrates. Most of the plant is discarded before it reaches the plate.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Artichoke hearts are the tenderest part, trimmed of everything that would have carried more. Jarred hearts are also boiled before packing, and boiling takes soluble oxalate away with the water.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Bamboo shoots are harvested young and always cooked in plenty of water before eating - a step taken for other reasons that removes soluble oxalate as a side effect. Canned shoots have had it done for you.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Black beans are low in oxalate as they are actually eaten, because boiling carries the soluble fraction off in the water; dry, before any of that, the load is moderate. Which makes the cooking liquid the thing to watch - the dark broth that gives a feijoada or a pot of Cuban beans its colour is where the oxalate went, and keeping it puts back what the boiling removed. Draining is the whole lever. Canned and rinsed has had it done for you. Quinteros measured that on the pulses themselves and found every cooking method lowers the soluble fraction, with microwave and industrial processing more effective than ordinary domestic cooking.

• Chai W & Liebman M, J Agric Food Chem 53 (2005), 3027-3030, which measured 30-87 % loss of soluble oxalate on boiling
• Quinteros A et al., Int J Food Sci Nutr 54 (2003), effect of cooking on pulse oxalate

Carrot is a root, and roots usually carry more than stems - but the carrot is an exception among them, low enough to be a staple of low-oxalate meal plans. Its leaves are another matter and are not eaten.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Dulse is not a land plant, and oxalate is something land plants make to manage calcium in soil. That is why dulse sits low here, and it is sold as flakes used like a seasoning, so the portion is a pinch on top of a level that was already low.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Edamame is not a dry bean, which is the whole of its position here: it is a soybean picked green and boiled in the pod, so the water treatment that lowers oxalate in the dry pulses has already happened by the time it reaches you, and the pod is not eaten. That is why it sits below the dried soybean it would have become. Salted in the pod, the salt stays outside; podded and stirred through a dish, you are eating the bean itself.

• Chai W & Liebman M, J Agric Food Chem 53 (2005), 3027-3030, which measured 30-87 % loss of soluble oxalate on boiling
• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8 (1999) 64–74, soaking and cooking reduce oxalate by leaching

Kimchi starts from cabbage, which is low, and fermentation does not create oxalate - bacteria make amines and acids, not plant minerals. What kimchi does add is the paste: chilli, garlic and ginger are spices, concentrated by weight and small by portion, and they are the only part of the jar that was not cabbage.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Lotus root grows in mud and is eaten sliced and cooked. It is low in oxalate, unlike the taro it often sits beside in the same cuisines - two starchy aquatic vegetables with opposite answers here.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Pinto beans come out low in oxalate once they have been boiled and drained, though the dry bean carries a moderate load and it is the water that takes it away. The catch is what usually happens next: refried beans are mashed in the liquid they were cooked in rather than drained, which puts back exactly what the boiling removed. Boiled and drained and refried are two different foods on this axis, from the same bean. Quinteros measured that on the pulses themselves and found every cooking method lowers the soluble fraction, with microwave and industrial processing more effective than ordinary domestic cooking.

• Chai W & Liebman M, J Agric Food Chem 53 (2005), 3027-3030, which measured 30-87 % loss of soluble oxalate on boiling
• Quinteros A et al., Int J Food Sci Nutr 54 (2003), effect of cooking on pulse oxalate

Sauerkraut starts from cabbage, which is low, and fermentation does not create oxalate - bacteria make amines and acids, not plant minerals. If anything the brine draws some of the soluble fraction out of the leaf, and the brine is usually not eaten.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Seaweed is not a land plant, and oxalate is something land plants make to manage calcium in soil. Seaweed lives in water already saturated with minerals and has no such problem to solve - which is why it sits low here despite being high on the mineral axes.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Shallot is a bulb, and bulbs sit low on this axis - the oxalate of an allium is in the green tops rather than the swollen base. The papery outer layers that carry most are thrown away.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans

Water chestnut is a corm grown in water rather than soil, and it stays low. It is also eaten raw or barely cooked, which matters less here than it would for taro - there are no oxalate crystals to disarm.

• Noonan S.C. & Savage G.P., Asia Pac J Clin Nutr 8:1 (1999) 64-74, oxalate content of foods and its effect on humans