From M., 28 June 2010 – spinach: why does it leave a fuzzy sensation in the mouth?
Q: When I cook spinach and silverbeet [chard] I tend to get a fuzzy feeling on my teeth. What’s happening?
A: Thanks for your question. Both spinach and silverbeet (chard) contain significant amounts of oxalate, a derivative of oxalic acid found in many foods, but especially members of the Amaranthaceae family. Your saliva contains, among enzymes and other electrolytes, calcium (1.2-2.8 mmol/L calcium). When oxalates in food come in contact with the calcium in saliva, the result is calcium oxalate – a precipitate with a gritty feeling. And that’s responsible for the fuzzy sensation.
Oxalates and oxalic acid bind to many metals during digestion – including iron and magnesium as well as calcium, decreasing their absorption by the body. What does this mean? As rich in iron and calcium as spinach might be, a portion of those nutrients binds to oxalate and cannot be used by the body.