How Boiling, Steaming, and Other Cooking Methods Affect Oxalate Content

Now that we have a pretty good idea of what oxalates are, where they're found, you have a list you can reference, and we know about the different qualities of food that can affect the oxalate content, we're going to talk a little bit about soluble versus insoluble oxalates.

Soluble Oxalate vs Insoluble Oxalate

In this post, I mentioned that oxalate is usually found in foods bound to things like sodium, potassium, magnesium, calcium. When oxalate is bound to sodium or potassium, one of the properties of the molecule that they form is that it's soluble in water, so we call sodium-oxalate and potassium-oxalate soluble oxalates.

When the oxalate is bound to magnesium or calcium, these molecules are much less soluble in water, so we call them insoluble oxalates. If you have kidney stones or you know someone who does, you may have heard of calcium oxalate before, because it's what many stones are made out of and may even be the reason many you are on this diet.

Calcium oxalate is a tiny, crystal-like molecule. When these crystals aggregate in the kidney, they eventually become the size of stones. If calcium oxalate was a molecule that was soluble then you could, in theory, just drink a bunch of water and dissolve your kidney stones — or they wouldn't even form or get stuck in the kidney to begin with. Either way, this is obviously not the case, and the same insoluble quality of that calcium oxalate applies when it's present in foods.

Just like there's a high variation in the amount of oxalate in foods, there's also a high variation in the percentage of insoluble to soluble oxalate content within a food.

For example, the oxalate in turmeric is mostly soluble, and the oxalate in cinnamon is mostly insoluble. The percentage of oxalate that is soluble versus insoluble is another thing that you can check for in a lot of different foods if you have TLO spreadsheet.

How Boiling Food Affects Oxalate Content

This is good to know when it comes to boiling foods. When the oxalate that's present in a food is mostly in insoluble form, or bound to magnesium or calcium, you can boil it in water, and just like your kidney stones don't dissolve when you drink a bunch of water, putting the food into water will not dissolve any of the insoluble oxalates. As a result, foods that have mostly insoluble oxalates won't have their oxalate content reduced by much if you were to boil them.

On the other hand, if the oxalate in the food is mostly soluble (bound to sodium or potassium), then you can boil the food and some of these molecules will split up and dissolve into the water.

If you were to boil a food like carrots, which have a high percentage of soluble oxalate compared to insoluble, and are high oxalate when they're raw, it would lower the oxalate content enough to make them low or medium oxalate. Some of the soluble oxalate molecules will dissolve into the water, and as long as you discard the water, your carrots will have a lower oxalate content than when you started.

Boiling vegetables does get rid of some of the other nutrients, but you can decide how long to boil based on how fibrous the vegetable is and how much of a tradeoff of oxalates versus other nutrients you're willing to have — 5-10 minutes is usually a good place to start. Just make sure you discard the water afterwards, and that will make any high-percentage-soluble-oxalate food lower in oxalate.

When you're boiling food, the smaller the pieces are or the more surface area of the vegetable that is in contact with the water, the better the chances will be of removing as much oxalate as possible. This is why steaming vegetables is also effective in removing some oxalate.

How Steaming Food Affects Oxalate Content

If you don't want to boil your food, but still want to remove a little bit of the oxalate that's present, you can steam it instead. It isn't as effective as boiling, because very little water is actually coming in direct contact with the vegetables for the oxalate to dissolve, but it does help more than eating veggies raw, roasting them, or cooking them in oil.

For some reason, there is some discrepancy around this topic. I'm not sure why, but it may have something to do with the fact that some vegetables shrink in size when they're steamed or cooked.

For example, if you look at the TLO list, you might notice that something like steamed cabbage will have less milligrams of oxalate per 100 grams than raw cabbage. This makes sense because some soluble oxalate comes out during steaming.

A half a cup of steamed cabbage, however, will have more oxalate than half a cup of raw cabbage because steamed cabbage shrinks in size when it's cooked and you can literally fit more steamed cabbage than raw into a measuring cup.

Either way, steaming doesn't increase oxalate levels — it may not necessarily decrease it, but it shouldn't increase it. If you eat half a cup of raw cabbage for lunch, then take another half cup of cabbage, steam it and eat it for dinner, you’ll have eaten less oxalate for dinner than you did for lunch.

How Sautéing or Roasting Foods Affects Oxalate Content

I want to mention a few other cooking methods really quickly. People will sometimes assume that if boiling and steaming can reduce the oxalate content of some food that other cooking methods should as well. But remember, the only reason that these two methods are sometimes effective is because water comes in contact with the soluble oxalate in the food, and the oxalate is able to dissolve into the water.

This means that if oil comes in contact with a food (like in sautéing) or nothing comes in contact with it (like in roasting), then these methods won't reduce the oxalate content. This doesn't necessarily mean that you shouldn't sauté or roast your food. It just means that you shouldn't count on these cooking methods to reduce the oxalate content of whatever you're eating.

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