Since about 70 % of all kidney stones are made up by calcium oxalate, avoiding fruit and vegetables that contain a high amount of oxalate might be part of any strategy to avoid the build up of further stones. It doesn’t mean however, that you have to avoid them altogether, as you will see later on.
What exactly is oxalate? It is a substance that occurs naturally in plants, animals and the human body. Chemically speaking it belongs to the organic acids, the exact formula being C2O42−. There are two sources of oxalate for the human body. First of all it is produced within human cells, the body converts certain substances (like Vitamin C for example) to oxalate. The second source are oxalate rich foods, like certain fruit and vegetable. Recent research has shown, that the oxalate intake has a relatively small impact, other factors, like intake of water, protein and calcium also play and important role. Rather than strict diets doctors tend to recommend a diet reduced in oxalate, with “as little oxalate as can be tolerated” without compromising too much quality of day to day life.
So if your doctor told you to avoid high oxalate food, here is a small list of some of the groceries that you should use with moderation: rhubarb, buckwheat, black pepper, parsley, poppy seed, eggplant, green beans, amaranth, spinach, chard, beets, cacao, chocolate (sad, but true), some nuts like almonds and soy products.
What about fruit? First some fruit containing a lot of oxalate, that should better be avoided: Kiwis, black- and blueberries, star fruit, the peel of citrus fruit, grapes, gooseberries, dried figs, raspberries, tangerines and red currants. You see, the list is not too long, there is quite a lot left to get your five a day!
Here a list of fruit low in oxalate: peeled apples, avocado, canned cranberries, green seedless grapes, lemon or lime juice, mangoes melons, cantaloupe, honeydew, watermelon, nectarines, papaya and raisins.
Fruit that contains a medium level of oxalate: apples with their peel, apricots, black currants, cherries, dried cranberries, grapefruit, grapes, oranges, peaches, pears, plums and prunes.
Whenever you eat something and get this funny furry feeling in your mouth (think of rhubarb or raw blackthorn fruit) there is a good chance it has to do with the oxalate in the fruit.
Following a diet low in oxalate is one stone in the mosaic that can help you prevent the development of new kidney stones. You should see your doctor though before going on a special diet in order to determine if your kidney stones are actually caused by too much oxalate in the urine. He also will tell you what to do about your protein and calcium intake, which are two other factors of significance. Eating more fruit with a low oxalate content might help you in your quest to avoid kidney stones, but they are just one part of the puzzle!