Summary
Oxalates are compounds present in a wide variety of plant foods. Some health influencers tell us that they can cause kidney stones — and that they prevent your body from absorbing essential nutrients. But how warranted are those claims? Here’s what you need to know about oxalates, and whether to include foods that contain them in your diet.
Notes from the above article:
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The kidney stones that contributed to Napoleon’s demise may have come (in part) from his almond consumption. But the medical field wasn’t quite as developed back then as it is today. And in the modern world, research is telling us that while high oxalate foods may contribute to the formation of some kidney stones, there are other factors that may be at least as significant.
It turns out that there are four basic types of kidney stones:
- Calcium phosphate kidney stones mainly result from animal protein-rich foods like meat, dairy, and eggs; fruit juices, sodas, and processed foods with added phosphorus; and excess sodium.
- Uric acid kidney stones are a result of too much acid in the urine. And they are mainly fueled by animal protein, sugary drinks, and alcohol.
- Cystine kidney stones are caused by a hereditary condition that causes cystine to leak into the urine. Research indicates that they can be fueled by drinking too little water, consuming too much sodium, and eating animal protein.
- Calcium oxalate kidney stones are the most common kind of kidney stone. They form when calcium in your urine combines with oxalates. Low-oxalate diets are sometimes prescribed for people who are prone to the calcium oxalate form of kidney stones. Adhering to such a diet generally means eating less than 100 mg of oxalic acid per day — which means no spinach (or beet greens or Swiss chard). When this diet is prescribed, it’s usually out of an abundance of caution because the role of dietary oxalates and calcium oxalate kidney stone formation is still inconclusive.
So if you’re worried about kidney stones, there is only one type that may be associated with oxalate consumption. However, oxalates don’t just come from the food you eat. In fact, about half the oxalates in your urine come from endogenous synthesis (which is a fancy way of saying that your body makes it by itself). What causes your body to make oxalates “endogenously”? Researchers believe that salt, animal protein, and excessive vitamin C are all associated with increased oxalate formation in your body, as measured by what winds up in your urine.
Oxalates can also bind to certain minerals in the gut, especially calcium, zinc, and magnesium, and prevent them from being readily absorbed. This is why it’s often considered an anti-nutrient. And is one reason why spinach, despite being high in iron and calcium, isn’t usually the best dietary source of these nutrients. Its high oxalate content can reduce the bioavailability of some of the minerals it contains.
So if you’re concerned about your calcium, zinc, or magnesium levels, you may want to moderate your oxalate consumption, and/or make sure you are eating plenty of these minerals from sources that aren’t especially high in oxalates. This is especially true with calcium because it can regulate dietary oxalate absorption. And low-calcium diets have been shown to increase the risk of calcium oxalate kidney stones.
An average single-serving (two cups raw or one cup cooked) of a high oxalate food is not enough to cause problems for most people. However, if you enjoy green smoothies every once in a while, I should note that oxalates do absorb more rapidly in liquid form. And while I certainly advocate eating your greens (and other healthy plant foods), it’s best to make sure that some of them are lower-oxalate greens, too, such as kale, collards, broccoli, arugula, romaine lettuce, parsley — frankly, any green that isn’t spinach, chard, or beet greens.
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This is more of a concern with calcium deficiency, as adequate calcium intake helps with the excretion of oxalates. As for iron, research suggests that oxalate intake doesn’t really seem to impact iron uptake from diet.
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astly, individuals with gut malabsorption issues — like short bowel, malabsorptive bowel disease, or Celiac disease — may benefit from a lower oxalate diet. In many cases, too few bacteria may be present in their digestive tract to degrade oxalates sufficiently.
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How to Reduce Oxalates in Food
If you fall into a category that requires more awareness of oxalate-containing foods in your diet, or just want to exercise caution, here are some tips to reduce dietary oxalates.
1. Eat calcium alongside high oxalate foods.
A normal calcium diet, which contains around 800-1000 mg per day, should be able to offset the potential effects of oxalates that can otherwise lower your calcium levels. For more on calcium, click here.
2. Increase your intake of magnesium.
You ideally want to consume foods that are high in magnesium in some proximity to your intake of high oxalate foods. Magnesium can also help reduce oxalate absorption when taken at around the same time. These effects disappear if your intake of magnesium and oxalate differ by 12 hours or more. You can take a magnesium supplement or potentially increase your intake of magnesium-rich foods, like whole grains, legumes, low-oxalate nuts, seeds, and greens. For more on magnesium, click here.
3. Cook oxalate-rich foods before eating them.
By the time most foods high in oxalates get to our plates, they may no longer contain enough to cause problems. Research suggests that boiling and steaming can significantly reduce oxalate content. One study found that boiling reduced oxalates in raw vegetables by 30-87%, and steaming reduced them by 5-53%. Roasting, grilling, or baking, however, may have little to no effect on oxalates.
4. Soak, sprout, or ferment oxalate-rich foods before cooking them.
A 2018 study found that soaking pulses (that is, the edible seeds of plants in the legume family) before cooking significantly reduced oxalate levels. The researchers found that approximately 24-72% of total oxalates in pulses appeared to be soluble, meaning their concentrations dissolved in water. Soaking taro leaves for 18 hours may reduce their oxalate content by 26%. And another study found that the fermentation of kimchi, using silverbeet (also known as chard), led to a significant reduction in oxalate content. Furthermore, there was a 72.3% reduction in the amount of calcium bound to insoluble oxalate in the kimchi.
Sprouting may also reduce oxalate content by up to 80% in red kidney beans. (However, it’s important to always cook kidney beans well, even if you sprout them, because they contain a type of lectin called phytohaemagglutinin that can be toxic. Fortunately, cooking destroys this and other harmful lectins.)
5. Drink enough fluids.
Staying hydrated with water can also help flush out oxalates and prevent dehydration, which can otherwise play a role in kidney stone formation for some people.
There’s No Need to Fear Oxalates
While some people may need to avoid dietary oxalates, particularly in large amounts, the evidence of their potential adverse effects on health is inconclusive. And for most people, many of the foods that contain oxalates are beneficial as part of a healthy, balanced diet. In fact, many oxalate-containing foods are some of the healthiest foods out there.
Regardless, if you’re worried about oxalates in your food, you have a number of ways to reduce their prevalence and absorption that still allow you to enjoy the healthy foods in which they’re found.
In other words, you can enjoy almonds and still conquer all of Europe, although I can’t imagine why you’d want to. Instead, perhaps, eat oxalate-containing foods in moderation (sticking to a standard serving), and work for a sustainable and just food system for all.
From comments:
Here https://pubmed.ncbi.nlm.nih.gov/15826055/ is an article that talks about the reasoning behind boiling vegetables high in oxalate.
Cucumbers are low in oxilates, but are helpful for bones.
Hello Lynn. That's a great question. I would ask your primary care doctor. Not only should they have the answer, but they also might be able to pull the necessary tests for you. Yours in health -Laura, Food Revolution Network Impact Team
Correct, it shows how much calcium is in our blood which is not a good measure. We don’t want a lot in our blood, we need vitamin k to direct it into our bones.
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