Why does eating cooked spinach make my teeth feel funny?
Spinach contains a large amount of oxalate crystals – mineral salts of oxalic acid. When spinach is cooked, especially canned, heat-processed spinach, some of the spinach cell wall structure is damaged and oxalate crystals leak out. It is this oxalate that gives your teeth and mouth that fuzzy coated feeling.
Spinach is also rich in calcium, and calcium oxalate crystals deposit on the teeth, coating them with plaque. Not much oxalate is released when eating fresh spinach because you chew it for only a short time.
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People who have problems with kidney function should avoid spinach and other foods that contain oxalate, because of the increased risk of producing oxalate stones in their kidneys.
Johan Uys, Bellville, South Africa
Spinach contains oxalic acid, which combines with the calcium in your saliva to produce the furry feeling on your teeth. Rhubarb, chard and beetroot leaves will all do the same.
Nigel Jones, Littlehampton, West Sussex, UK