Oxalic acid is found in many plants, and even formed in our bodies with the metabolism of some toxins. It is a highly reactive chemical, forming various oxalate crystals as it chelates (binds with) minerals during digestion of the plants in which it is found.
The problem is, these are essential minerals (calcium, magnesium, iron, sodium and potassium) which, once bound with the oxalic acid, are rendered useless to the enzymes that need them. In this state, they are not assimilated by the body’s blood and tissues where needed.
This makes oxalic acid an anti-nutrient.
But how concerned should we be getting about specific levels of oxalic acid in various foods?
As I began juicing, I suddenly found myself wondering if I might be getting excess oxalic acid along with those wonderful concentrated micro-nutrients. Could it be counteracting my juicing efforts?
So I went on an expedition, and ended up with this post. But as a result of simply answering the juicing question, added a post on how to mitigate oxalic acid intake when juicing.
How Normally Excreted Oxalates Become Toxic
Oxalic acid forms tiny oxalate crystals corresponding to the mineral with which it has bonded, which are normally passed through the lower intestine to be excreted with waste.
But although we normally do a good job of getting rid of oxalate waste, an excess can build up, creating health hazardous.
A buildup of calcium oxalate crystals for example, which are normally excreted through the urine, can ultimately form kidney stones (80% of cases of kidney stones are estimated to originate from calcium oxalate).
Excess oxalic acid buildup has also been linked to symptoms ranging from inflammation in the joints, arthritis, fibromyalgia, interstitial cystitis or burning urine flow, burning bowel movements, and ‘leaky gut’, to name a few. 
A study done in Poland even showed that autistic children exhibited extremely high oxalate levels in their blood and urine, however without any markers of kidney stone risks or disease.
The Confusing Oxalate Conundrum
Oxalic acid is a natural defense mechanism for the plants it occupies, imparting a sharp, bitter taste, particularly noticeable in the older leaves of spinach, beets, kale and rhubarb (which is so high that its leaves should not be consumed at all), making it unappealing to insects and animals.
Moreover, high oxalate foods are tolerated by most of us as long as not extremely excessive consistently over long periods.
But it is confounding when many tables from trustworthy sources disagree on amounts of oxalic-acid content of any particular food. This is because the amounts will vary depending on the part of the plant, the soil in which they are grown, and the age of the plant (older growth will typically have higher oxalic acid).
More questions also arise, such as what is the ratio of oxalic acid does it take to neutralize how much of a particular mineral? Are any minerals left over?
Some cancer therapy diets even disallow any moderately high oxalate foods due to the interference with vital nutrient absorption.
But oxalic acid from one food does not appear to bind to minerals from other sources consumed in the same meal (for example, the calcium in dairy is absorbed while the oxalic acid in spinach interferes only with the calcium in the spinach).
The Up Side of Oxalates
The good news is that since most foods considered extremely high in oxalic acid (and thereby worthy of caution) are also extremely high in the mineral with which it bonds.
And most high oxalic acid foods are also extremely high in other very important nutrients making the idea of avoiding them completely nonsensical.
So while most healthy people have no issue expelling oxalate waste from their bodies, why be concerned?
Nobody should or would ever want to sit down and consume a few rhubarb greens, or a pound of spinach, or a dozen beets with a side of parsley, several ounces of chocolate, a handful of peanuts, and spinach and beet green salad with soy beans every day on an ongoing basis. If someone did, they may actually be accumulating an excess of oxalate waste.
Those suffering from conditions associated with excessive oxalate levels will be concerned with managing levels or even eliminating oxalic acid in their diets. And in many of these individuals, symptoms that may often be reversed.
Foods high in oxalic acid should be avoided altogether by those potentially compromised by oxalic acid intake (such as a kidney patient).
Oxalic acid also results from metabolism of of high amounts of glucose, toxins or heavy metals such as cadmium, and so environment and stress can also increase the risk of excess oxalate buildup for people with an excessive exposure to those factors.
And if you are on anti-biotics, the neutralization of oxalates in the lower intestine is impeded, so a multi-strain probiotic containing oxalobacter formigenes, the primary oxalate reducing bacteria should be taken in between doses of anti-biotics, and for a few weeks after the anti-biotic regimen is complete.
Oxalic Acid: How Much is Too Much?
And the amount of oxalic acid varies in plants from extremely low to extremely high. “High oxalate” is defined between 100 and 900 mg per serving (typically 100g, 1/2 cup or 3.5 oz.).
Foods high in oxalate (100–900 mg per serving) include:
- Star fruit
- Beet greens
- Rhubarb greens
- Swiss chard
- Cocoa powder
- Collard greens
- Sweet potatoes
- Turnip greens
People who are healthy should not avoid spinach altogether, as this might be more like throwing the baby out with the bathwater! Spinach is a powerful source of magnesium, potassium, folate, carotenes, vitamin C, vitamin K and lutein.
So do eat spinach if you can, in moderation, or substitute kale.
There are still plenty of high calcium, low oxalate content foods to eat! To name a few believed to be low in oxalate and high in calcium:
- Kale (with a whopping 139mg of very absorbable calcium per 100g serving)
- Bok Choy
- Snap peas
- Dairy products
What if You Need to Go Low on Oxalic Acid?
Please note that caution is advised against undergoing a diet suddenly focused on extremely low oxalates. Apparently this can cause a sudden detox as the body dumps oxalate stores, causing an intensification of symptoms associated with high oxalate.
Of all the high oxalate foods, the ones you really want to watch are the ones with the very highest amounts. Here is a good reference chart for oxalic acid content in just about all foods, and here is a good list of vegetables by high and low oxalic acid.
While cooking does neutralize oxalic acid, even cooked spinach yields almost the same as raw spinach. Some foods may not be practical to cook, or sufficient for someone trying to avoid oxalate rich foods.
But cooking over 118 degrees destroys live enzymes, and so also inhibits mineral absorption. But some foods such as spinach are still nutritious enough lightly cooked to be well worth the trouble of inclusion!
If you’re just looking to not go overboard when you’re juicing, I wrote this post on a “low-oxo” green juice recipe that I really like and a list of good veggies for low oxalic acid juice.
But, if your medical condition requires you to go low-oxalate, remember there are a lot of varying reports on the topic, so here is a good summary of what you’ll find along with a low-oxalate diet.