Grains and oxalates: 30 foods rated

Popcorn is high in oxalate by weight (about 54 mg per 100 g air-popped, 41 mg oil-popped) because popping removes the water and concentrates it — fresh sweetcorn is only about 1 mg per 100 g. Popcorn is very light though, so a cup weighs roughly 8 g and carries only 4-5 mg. A small bowl is modest; a large sharing bag is not.

Quinoa is high in oxalate, and the rinsing everyone does before cooking it - to remove the bitter saponins - takes some of the soluble fraction with it. Cooking in plenty of water and draining takes more; cooking it absorbed, pilaf-style, takes none.

• 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)

Buckwheat is not a wheat and not a grass - it is a seed related to rhubarb and sorrel, which is the family this axis is named after. That relation is not a coincidence: the plants that store oxalate tend to be related, and buckwheat sits with them.

• Gad S et al., Food Chemistry 8 (1982)

Nuts and wholegrain cereals are the two food groups the oxalate literature flags most, and a muesli puts both in the same bowl.

Rye carries oxalate in the same place wheat does - the outer layers - and rye is almost always eaten wholegrain, because a white rye flour makes a bread nobody wants. The grain that is rarely refined is the grain that keeps its bran.

• Gad S et al., Food Chemistry 8 (1982)

Whole wheat carries its oxalate in the bran layer, so the level depends entirely on how refined the flour is - white flour has had that layer removed. Siener measured that layer: whole grain wheat runs 53.3 to 76.6 mg of total oxalate per 100 g across three species, and the bran alone 457.4. This is one of the few axes where the refined version of a grain is the gentler one.

• Israr B et al., Food Chemistry 141 (2013), 1690-1693, on phytate freeing soluble oxalate by binding calcium
• Gad S et al., Food Chemistry 8 (1982)
• Siener R et al., J Agric Food Chem 54:8 (2006) 3008-3011, oxalate content of cereals and cereal products

Wheat bran is where the grain's oxalate and its phytate both sit, and the second matters as much as the first because phytate binds calcium, and calcium bound to phytate is calcium not available to bind oxalate. Bran works against the standard remedy for this axis. Israr measured both in the same samples: across wheat, barley and oat bran, total oxalate ran 33 to 199 mg/100 g and the soluble part 14 to 79, with phytate from 227 to 4,393 mg/100 g — enough, in every food tested, to raise the soluble share by binding up the calcium. The soluble part does not follow the total, which is why the phytate matters. Two published figures for wheat bran do not agree: Siener measured it alone at 457.4 mg per 100 g, several times Israr's range for a set of three brans.

• Israr B et al., Food Chemistry 141 (2013), 1690-1693, on phytate freeing soluble oxalate by binding calcium
• Gad S et al., Food Chemistry 8 (1982)
• Siener R et al., J Agric Food Chem 54:8 (2006) 3008-3011, oxalate content of cereals and cereal products

Amaranth is not a grass and has no bran and endosperm in the way a cereal does — it is an Amaranthaceae, the family of spinach and beetroot, which are the two foods this axis is best known for. The relation is worth knowing and it is not the whole answer: those plants store their oxalate in the LEAF, and amaranth grain is the seed. Amaranth leaves, eaten as a vegetable in several cuisines, are a different food from the seed sold as a grain.

• 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

Barley bran was one of the three cereals Israr measured, and across that set total oxalate ran 33 to 199 mg/100 g with 14 to 79 of it soluble — so none of the three is at zero. No figure for barley alone is published, so this level is a ranking rather than a measurement.

• Israr B et al., Food Chemistry 141 (2013), 1690-1693, phytate, minerals and oxalate in bran cereals and legumes

Bulgur is cracked wheat that keeps part of its bran, and that is where the oxalate is: a study of cereals and their milling products concluded that oxalic acid sits primarily in the outer layers of the grain, with whole grain wheat running from 53.3 to 76.6 mg per 100 g of total oxalate and wheat bran alone reaching 457.4, the highest it measured. That study names bulgur among the whole grain durum products it found comparably high. How much any given bulgur carries therefore follows the grinding: a fine pale grade has had more of the bran taken off than a coarse dark one.

• Siener R. et al. (2006), oxalate content of cereals and cereal products by HPLC-enzyme-reactor — figures for the three whole grain wheat species and for wheat bran, with the other products named only as comparably high, so no number can be quoted for bulgur itself

Sweetcorn is one of the lowest-oxalate grains, around 1 mg per 100 g boiled. The oxalate sits in the outer layers, so corn bran and cornflakes are low too. Popcorn is the exception: popping concentrates it.

Corn bran is the bran itself — the layer where a grain keeps its oxalate, sold separated from the endosperm that carries almost none. It is the concentrated fraction and not the whole grain, and maize starts low enough that even its bran stays here. The phytate that comes with any bran binds calcium, and calcium bound to phytate is calcium not available to bind oxalate.

• 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

Couscous is rolled durum semolina, so what it carries on this axis turns on one thing: whether that semolina was refined or wholemeal. Oxalate in wheat is concentrated in the outer layers of the grain, so it goes with the bran — and the study of cereal products that names couscous puts it among the whole grain durum products it found comparably high to whole grain wheat's 53.3 to 76.6 mg per 100 g. The pale couscous on most shelves is made from refined semolina, with most of that bran milled away, so the packet decides which of the two foods is in the bowl.

• Siener R. et al. (2006), oxalate content of cereals and cereal products — it names couscous among the whole grain products and publishes no figure for it, and it does not separate the refined grade from the wholemeal one

Durum wheat reaches the kitchen as semolina, and semolina is the endosperm with the bran milled out — the bran being the fraction that carried the oxalate. A wholemeal durum flour is a different answer from the semolina that makes pasta, and the pasta is what most of this grain becomes.

• 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

Khorasan wheat is sold as a wholegrain almost without exception — being unrefined is what it is bought for — so the bran that carries the oxalate is still in the flour. That is the opposite of durum, which reaches the shelf as semolina with the bran already gone.

• 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

Millet is hulled but rarely debranned: at that grain size the layer carrying the oxalate is too thin to separate, so what goes in the pot is close to the whole grain whatever the packet says. Soaking it overnight, which is done for the cooking time, takes part of the soluble fraction into 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

Oats are not free of oxalate: Israr measured the highest soluble oxalate of the study in oat bran, 79 mg/100 g. The bran is the fraction and not the whole grain, so a bowl of oats carries less than that figure — but not zero. The oat is also high in phytate, which binds calcium and so keeps more of the oxalate soluble than the total alone suggests.

• Israr B et al., Food Chemistry 141 (2013), 1690-1693, phytate, minerals and oxalate in bran cereals and legumes

Oat fibre is milled from the hull and the outer layers, which is where a grain keeps its oxalate rather than in the endosperm. It is not eaten as a food: it goes by the spoonful into breads and bars to raise their fibre, and that portion is what keeps it here rather than its concentration.

• 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

Rolled oats are the whole grain flattened rather than separated, so the bran — where a grain keeps its oxalate — is still there. Rolling changes the cooking time and nothing on this axis. The oat is also high in phytate, which binds calcium and so leaves more of the oxalate in the soluble form.

• 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

Wholegrain flours carry more oxalate than white ones and rye bread is usually wholegrain, but no figure for it is published.

Sorghum is eaten whole far more often than refined — it is boiled like a grain or milled into a wholegrain flour — so the bran that carries the oxalate stays in it. The phytate in that bran binds calcium, and calcium bound to phytate is calcium not available to bind oxalate.

• 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

Spelt bread is usually milled wholegrain, and wholegrain flours carry more oxalate than white ones, but no figure for it is published.

Wheat gluten is isolated protein: the starch is washed out and the bran was never in it, so the fraction of the grain that carries the oxalate is not part of this ingredient at all. What is left is close to pure protein, and this axis has almost nothing in it to measure.

• 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