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Oxalates - Can You Eat Too Many Leafy Greens?

Eat your leafy greens is a great mantra to live by for a long and healthy life. Platefuls of lettuce, and kale, and spinach, and chard, will surely keep you feeling nutritionally strong and ready to take on the world, for ever and ever. Yes, it can seem the route to world domination is, in fact, through consumption of leafy greens.

Ah, but hold on there... Let’s check this theory out. Can there be too many leafy greens? Well, like many things in life, it’s possible to have too much of a good thing…especially when it comes to the oxalates found in some green leafies.

What Are Oxalates?

Oxalates, you ask, what pray tell are those? Oxalates (or oxalic acid) are a naturally occurring compound in foods like spinach and chard, beet greens, raspberries (oh no!). They are also produced in small amounts by the liver. Oxalates belong to a group of compounds called anti-nutrients whose function is to provide protection for plants against predators – everything from harmful bacteria to insects, animals, and even humans.


Anti-nutrients provide protection to plants in a few different ways. First, anti-nutrients often cause a bitter taste in foods that deters people and animals from eating them (think the bitter flavor of beet leaves, which are very high in oxalates). Beyond just a bitter flavor, anti-nutrients can also prevent the proper digestion and absorption of foods. When you consume large amounts of anti-nutrients in plant foods, they prevent you from absorbing any beneficial nutrients that are present in the rest of the food.

Oxalates specifically bind to other minerals (like calcium) and prevent your body from accumulating too much of them. There is 115 mg calcium in half a cup of cooked spinach, but because of the interference of oxalic acid, you would have to eat more than 16 cups of raw, or more than eight cups of cooked spinach, to get the amount of calcium available in one cup of yogurt.

How Oxalates Affect Us

Consuming too many oxalates is directly correlated with the formation of the most common type of kidney stones – calcium oxalate stones. These form when oxalates bind with calcium in the bloodstream and pass through the kidneys into urine. If you’ve had kidney stones, you know it – they are incredibly painful. The worst thing about kidney stones is that if you’ve had them once, you’re more likely to develop them again. That’s why, if you do develop stones, your doctor might recommend a low-oxalate diet with the goal of keeping oxalate intake below 50-100 mg per day.

For most people, consuming oxalates isn’t a big deal because the oxalates are simply excreted as waste. People with an inflammatory condition like rheumatoid arthritis, lupus, Crohn’s, celiac, or leaky gut may find symptoms worsen with oxalate consumption. Anyone with reduced kidney function such as with diabetes would also be wise to really cut down on foods that contain oxalates. High salt diets may also trigger kidney stones by upping the amount of calcium in your urine.

Increased intestinal permeability, or “leaky gut” as it is commonly called, occurs when the tight junctions between the cells that make up the intestinal lining are damaged and become loose. Gaps between the cells allow large particles that should remain in the digestive tract to seep into the bloodstream. In people with a healthy gut, only a very small amount of the oxalates consumed from food are absorbed into the bloodstream from the gut. However, in people with leaky gut, intestinal dysbiosis (abnormal bacteria in the gut) or inflammation, the rate of absorption of oxalates might rise from the normal level of 1 to 2 percent to as high as 40 to 50 percent.

Where Are Oxalates Hiding?

Probiotics have been shown to block the absorption of oxalate1. It’s just one more example of how important a healthy gut and diverse microbiome are for the health of our entire body. Hundreds of conditions – from kidney stones to migraines to skin disorders, depression, fatigue, and more are linked to gut health.

The weird thing though, is that some of the healthiest foods – beans, nuts, and seeds, green leafies, blueberries, dark chocolate (oh yes, it’s good for you), do have oxalates in them. So, what to do, what to do? Well, moderation is everything, you can still eat foods that contain oxalates, it’s about making sure that you don’t overload your system with too many. A green smoothie loaded with raw spinach and blueberries is still something you can enjoy – just not every day. Most healthy people who eat a varied diet don’t need to worry about oxalates. They’ll consume, on average, 200-300 mg of oxalates per day with no health issues as a result.

If you’re worried about over consuming oxalates – either because of a leaky gut, your diet, or a combination of both – the most important thing you can do is not panic. Kale, blueberries, and sweet potatoes are still healthy foods – and they still have a place in your diet. They contain important nutrients, vitamins, minerals and phytochemicals. Remember, oxalates may even have some benefits that science hasn’t caught up to yet.

Oxalate Action Steps

  • Get started healing your gut. You can read more about healing your gut in this blog.
  • Cook, soak, ferment, and sprout your food. All of these steps help to reduce the content of oxalates and other antinutrients in your food.
  • Use a low-oxalate greens powder to provide the important nutrients and phytochemicals that high-oxalate foods provide, without the oxalates. e.g. Dr. Cowan’s Garden Low-Oxalate Greens Powder
  • Instead of in a smoothie, sprinkle greens powder over eggs, mixed in a mug of bone broth, rub onto meat, use as a seasoning for roasted or steamed veggies.
  • Lowering your saturated fat intake will help decrease intestinal oxalate levels. Fat prevents calcium from removing oxalates in the body.2
  • Drink 2 to 3 liters of water a day combined with calcium citrate to help remove oxalates. Use citrates in the form of citrus fruits with no sugar added. Squeezing ½ lemon in a glass of water works great, spread it over the whole day to regulate how much calcium you are getting.
  • Make sure you get your fish oil; omega 3 help degrade oxalates. Omega 3’s are synthesized into anti-inflammatory prostaglandins which help reduce overall inflammation in the body.

If you have been eating a diet high in oxalates and decide to make a change – it’s generally accepted that doing so slowly is a good idea. If you wean yourself off gradually you can often avoid the joint pain and rashes which can happen if you decide to go Cold Turkey on your Green Leafies.

  1. Probiotics and Other Key Determinants of Dietary Oxalate Absorption1. Michael Liebman* and Ismail A. Al-Wahsh Adv Nutr. 2011 May; 2(3): 254–260.
  2. Lorenz, E, Michet, C, Milliner, C, and Lieske, J, Update on Oxalate Crystal Disease, Current Rheumatology Report, 2013 Jul; 15(7): 340.