Spinach, beets, chocolate, and almonds. These are common foods people with kidney stones are told to avoid due to high oxalate levels. Yet oxalates are tied to many other high oxalate symptoms other than kidney stones and kidney issues.
Restricting high oxalate foods is the main way to reduce these symptoms.
Since oxalates are prevalent in all plant foods – dark leafy vegetables having some of the highest levels – reducing oxalates with food restrictions can be impacting. Nevertheless, adequate planning can ensure that a variety of low-oxalate food substitutes that are rich in nutrients.
Still, if there was a way to keep some high-oxalate foods that are culturally relevant, readily accessible, or enjoyable, then this may be a little easier for people and add more pleasure back into food.
There is a way!
It involves fermentation and sprouting. Before learning how much these methods reduce oxalates, let’s learn a little about oxalates and how they can harm the body.
Table of Contents
What is oxalate
All plants produce oxalic acid in various levels. It is their natural self-defence against insects and other pests.
When oxalic acid binds calcium, iron, or magnesium, it forms oxalate crystals. Once bound to oxalate, these minerals are no longer available for absorption. This is why oxalates are considered antinutrients and can cause calcium or iron deficiency even when you eating calcium-rich or iron-rich foods.
Oxalates have the strongest attraction to calcium compared to iron or magnesium. The corresponding crystal is called a calcium-oxalate crystal, and it is the most common cause of kidney stones.
Sources of oxalate
Oxalate from foods
Diet contributes the highest amount of oxalate to our overall oxalate load. A typical English diet contributes between 70-150 mg of oxalates (1). To put high oxalate foods into perspective, 100 mL of beetroot juice delivers 800-1000 mg of oxalic acid. A low oxalate diet limits oxalates to 40-50 mg per day.
Eating the following foods too often or in large portions can quickly overload the body of oxalates:
- beans: navy, black, and pinto
- beetroot and greens
- potato, sweet potato, yams
- raw carrots
- sesame seeds
- wheat bran
Oxalate produced in the body
Besides food sources, the body also makes oxalate with the majority made in the liver. This can be minimized by ensuring adequate vitamin B6 status, because shifting the reaction away from oxalate production requires an enzyme that depends on vitamin B6 for full function (2).
Enzymes that process oxalates for removal from the body require vitamin B6. That means people with low vitamin B6 won’t have the ability to properly clear oxalates compared to people with good nutritional status.
Oxalate from fungi or yeast
Yeast and fungi in the body can also convert sugar into oxalates. In addition, Candida albicans can convert collagen in the gut to substances that can form oxalate (3) in people with low B6. This can explain why people with Candida overgrowth commonly experience high oxalate symptoms as well. Both conditions go hand in hand.
What are some high oxalate symptoms?
The most common symptom associated with oxalate is kidney stones. If free oxalate and calcium bind in the urine, the resulting crystal can settle out and may form a kidney stone (1).
Calcium-oxalate crystals can also lodge into other tissues in the body such as blood vessels, bones, joints, central nervous system, and organs. Below is a list of symptoms from oxalate with or without binding to calcium (4).
- joint pain or stiffness
- inflammatory bowel disease
- irritable bowel disease or symptoms of
- brain fog; poor memory
- difficulty concentrating, focusing; impaired focus
- kidney stones
- mineral deficiencies
- osteoporosis or brittle bones
- slow to heal
Who is at highest risk for harm from oxalate?
Once aware of symptoms associated with high oxalate levels, some people will immediately notice the link between their symptoms and foods. Nevertheless, other people will continue eating foods with high to moderate levels of oxalates and feel quite well.
People with the following conditions are the most susceptible to harm from oxalates (3).
- Digestive issues: Increased intestinal permeability (leaky gut) can cause more oxalate absorption through intestinal walls. Similarly, alteration in the composition and number of microbes in the gut (dysbiosis) may also increase the impact of oxalates.
- Antibiotic usage: Antibiotics can’t discriminate between good and bad bacteria. As a result, heavy doses or frequent use of antibiotics may significantly reduce the number of oxalate-degrading bacteria in your gut.
- Kidney issues and kidney stones: Oxalates are a known cause of kidney stones, but any sign of kidney stress should be a possible sign of oxalate overload.
- Bariatric surgery: Patients with a Roux-en-Y gastric bypass have increased absorption of oxalates from the intestine. The exact reason for this is unknown.
- Deficiencies: vitamin B6, magnesium, thiamine
How is oxalate removed from the body
In ideal situations, bacteria in the intestine degrade the majority of incoming oxalates. Only 2-12% of oxalate is absorbed from foods through the gut into the bloodstream (1).
Oxalobacter formigenes is a prominent oxalate-degrading bacteria that colonizes the gut (5) during infancy as infants interact with their environment. In addition, some strains of lactic acid bacteria found in the gut also have ability to degrade oxalates and maintain low oxalate levels (5).
However, antibiotics and other medications, high stress, and poor diet damage bacteria in the gut. Killing off oxalate-degrading bacteria impairs your ability to deal with oxalates from foods, potentially causing high oxalate symptoms.
This is exactly what one study found. After following 5010 nurses over the long term the results showed that taking antibiotics for more than 2 months in early adulthood or middle age is associated with higher risk for kidney stones later in life (6).
Keep in mind that kidney stones is only one high oxalate symptom. There were likely countless other nurses in this study with other symptoms not recorded.
These results emphasize the need to minimize damage to our microbes and restore gut health after taking antibiotics and other medications known to kill microbes.
Other than bacterial removal, the remaining oxalates exit the body through urine and poop in best case scenarios.
Solutions for high oxalate symptoms
When oxalate levels build up and high oxalate symptoms begin to show, people need therapeutic interventions to feel normal again.
Reducing oxalates coming into the body through diet is the most helpful way to reduce symptoms. This involves removing all high oxalate foods until your diet consists of mainly low oxalate foods and some moderate ones.
Low oxalate coming into the body signals to cells that they can dump oxalate crystals. If high oxalate foods are eliminated abruptly, symptoms will flare as oxalate crystals dislodge from tissues too quickly. Instead, a gradual reduction is essential to prevent distress. For example, you may try removing one or two high oxalate foods from your diet per week.
The discovery of oxalate-degrading bacteria in the human gut sparked interest in identifying strains for use in probiotic treatments.
The most obvious bacterial strain to use as a probiotics to reduce oxalate is O. formingenes due to its natural presence in the gut and ability to degrade oxalates. Several human studies have trialed this probiotic with mixed results in reducing output of oxalate in urine (7, 8, 9).
Four strains of lactic acid bacteria showed promising for use in probiotics to reduce oxalates. Some of the strains had oxalate degrading activity to deal with the root problem. Other strains had anti-inflammatory activity to deal with the effects of high oxalates (10).
Another test tube study found a strain of Lactobacillus acidophilus that had oxalate-degrading enzymes, suggesting its potential use in humans (11).
As with most things in science, we are waiting for human research to confirm the results from test tube studies. High quality research has yet to determine whether whether forking out money on these potential probiotics is worth the coin and effort.
Food preparation methods
- Sprouting: Germinating seeds, grains, or pulses (beans, peas, lentils) activates enzymes that have the ability to breakdown oxalate. For example, soaking soybeans then sprouting reduced oxalates, and cooking reduced oxalates even further (15).
- Boiling: Free oxalates are water soluble and leach into the cooking water. When compared to other cooking methods, the loss of oxalate was greatest through boiling (40-50%) versus steaming (20-25%) versus baking (12-15%) (18). Unfortunately, B vitamins and vitamin C are also water soluble and are lost with cooking.
- Soaking: Another way to leach oxalate from foods is to soak grains and legumes before cooking. Add a tablespoon of apple cider vinegar or lemon juice to draw more antinutrients into the soak water. Always discard this water; do not use for cooking.
- Steaming: Compared to sprouting and boiling, steaming is not a very effective way of reducing oxalate, but it does lose some. Only 20-25% of oxalate were lost with steaming (18).
- Baking: The least effective method is baking with 12-15% loss (18).
If you don’t have time for sprouting, at least soak and cook seeds to reduce oxalates. Losses won’t be as high as soaking, sprouting, then cooking seeds, but soaking before cooking still helps.
Does fermentation reduce oxalates in food?
Thankfully, many of the bacteria investigated for probiotic treatment are prominent strains in fermented vegetables. As such, several studies investigated the effectiveness of fermentation to reduce oxalate levels.
A few researchers looked at the effectiveness of fermentation to reduce oxalate in these foods when they are milled into a flour.
One study saw a 58-65% reduction in oxalates from fermenting taro flour for various lengths of time (12). Similarly, two different species of yams showed a 58% and 66% decrease in oxalates when ground into a flour and fermented for 48 hours (13).
Although most North Americans don’t use taro or yam flour, these studies give promising evidence that fermentation is an effective way to reduce oxalates in other flours like whole wheat or buckwheat flour while making sourdough bread.
Oxalate reduction through fermentation isn’t limited to flour. It is effective for reducing oxalates in high oxalate vegetables, such as swiss chard.
A study investigating oxalate levels in kimchi made with white swiss chard showed a significant reduction. Swiss chard made up 57% of the total ingredients in kimchi; therefore, it contributed the most oxalates.
The first oxalate reduction happened while preparing swiss chard. After 11 hours of soaking the leaves and stems in a 10% brine, total oxalates reduced by 13%. Then, after mixing the chard with other ingredients and spontaneously fermenting for 5 days, total oxalate levels reduced even further by 38% (14).
Reasons for the reduction in oxalate level are owing to reduction in pH, which is a hallmark feature of fermentation. Acidic environments cause calcium in oxalate crystals to break away from oxalate. This free form versus the bound form serves as “food” for oxalate-degrading bacteria. Therefore, as long as oxalate is not bound to calcium, bacteria can use it for energy.
Spontaneous fermentation shows greater loss of oxalate than controlled fermentation using a starter culture (15).
The combination of acidic pH and oxalate-degrading bacteria make fermentation a valuable method for lowering oxalate content in otherwise high-oxalate foods. This gives people who require a low-oxalate diet the most effective way to lower oxalate and have the freedom to enjoying high-oxalate foods without worrying about insidious effects.
Gut health to reduce high oxalate symptoms
More than degrading oxalates, microbes found in raw fermented foods contribute to gut health. As noted earlier, the reason why people develop high oxalate levels in the first place is due gut dysbiosis and intestinal permeability.
Raw fermented foods offer high levels of good microbes that can reinstate microbial balance. Microbes also produce compounds that calm inflammation, reduce permeability, and heal the gut lining.
Kimchi in particular offers the highest level (107 to 109 CFU/gram) of lactic acid bacteria compared to three other types of fermented vegetables (14).
To target the root of high oxalate levels, people need to regularly consume raw fermented foods with live microbes. Fermenting foods with high oxalates gives a double bonus of good microbes for the gut and reduced oxalate levels.
High oxalate symptoms span much further than kidney stones and kidney issues. They can be the cause of joint pain, poor memory, brain fog despite eating a healthy diet with green smoothies, nuts, whole grains, and beans.
A low oxalate diet and specific probiotics can reduce oxalate levels and dislodge calcium oxalate crystals in tissues. Fermenting high oxalate foods can reduce levels by nearly half. A combination of soaking, sprouting, and cooking also reduces oxalate levels.
Still, addressing the root of the problem is where fermented foods comes in. Eating a variety of fermented foods helps reduce inflammation and restore microbial balance in the gut while nourishing the body with nutrients to prevent another build-up of oxalates.