Oxalates
What slows things down
Salts that some plants accumulate, and that bind to calcium all the way to the kidneys.
Effects
They grab the calcium of the same meal: that of spinach is absorbed at only about 5%, against nearly 30% for that of milk. And in people who form kidney stones, dietary oxalate matters: calcium oxalate stones are the most common.
In the gut, oxalate binds to calcium in insoluble crystals that leave with the stool. A trial measured it with labeled calcium: 5% absorbed with spinach, 27% with milk (Heaney et al., 1988). Rhubarb, chard, sorrel, spinach and cocoa are the richest.
The oxalate that reaches the blood leaves through the kidneys; if it meets too much calcium in too little water there, it crystallizes. Calcium oxalate stones make up the majority of kidney stones.
By sex: kidney stones are about twice as common in men as in women. A useful paradox: eating enough calcium with meals protects better than a low-calcium diet, because it holds oxalate back in the gut (Borghi et al., 2002).
Sources: Heaney et al., AJCN, 1988 · Borghi et al., NEJM, 2002
The remedy
Boiling and DISCARDING the water removes a good half. A tendency to kidney stones is the only situation where this deserves real attention.
Where to find it (65)
- Abyssinian sorrel
- Agretti
- Allmania
- Almond
- Amaranth
- Bamba (Oxygonum)
- Beet
- Beet greens
- Begonia
- Bistort
- Buckwheat
- Cashew
- Caucasian spinach
- Celosia
- Chukka kura (bladder dock)
- Cocoa / very dark chocolate
- Curly dock
- Digera
- Four-leaf pink-sorrel
- French sorrel
- Garden orache
- Giant taro
- Good King Henry
- Huauzontle
- Ice plant
- Indian glasswort
- Japanese knotweed
- Knotgrass
- Lamb's quarters
- Mediterranean saltbush
- Mojave seablite
- Monk's rhubarb
- Mountain sorrel
- Mukunuwenna
- Nepal dock
- Nopal
- Okahijiki (land seaweed)
- Patience dock
- Pine nut
- Prickly pear
- Purple shamrock
- Purslane
- Quinoa
- Ravash (wild rhubarb)
- Rhubarb
- Romeritos (seepweed)
- Sea purslane (halimione)
- Sea purslane (sesuvium)
- Sea-blite
- Sericostachys
- Sesame seeds
- Sheep's sorrel
- Sorrel
- Spinach
- Sweet potato
- Swiss chard
- Taioba leaves
- Taro
- Taro leaves
- Tree spinach (magentaspreen)
- Water pepper
- White bean
- Wild alternanthera
- Wild knotweeds
- Wood sorrel