ARE HIGH-OXALATE FOODS BETTER AVOIDED FOR KIDNEY AND OVERALL HEALTH?

Medically Reviewed by Dr. Rosmy Barrios - August 14, 2024

If you have ever suffered from kidney stones, you may have heard of oxalate. Oxalate is a natural substance that is found in many foods and produced by your body. It can bind to minerals like calcium and form crystals that may cause kidney stones or other health problems.

In this article, we will explore what oxalate is, how it affects your health, and how you can manage your oxalate intake.

What is Oxalate and Where Does It Come From?

Oxalate is the insoluble salt of oxalic acid, an organic acid, both of which are present in almost all foods and are also made by the body. Dietary oxalate is considered an antinutrient due to its ability to bind to minerals and prevent the body from absorbing them. Plants contain oxalate and other antinutrients, like phytate and lectins, to protect themselves from predators. Some foods possess noticeably high amounts of oxalate, such as spinach, rhubarb, nuts, beans, chocolate, and tea.^[1]

When oxalate enters the gut, it is partially degraded by gut bacteria and bound partially to minerals, both of which promote its swift excretion. The remaining free oxalate is absorbed. The liver and kidneys produce enzymes to degrade oxalate naturally, following which it is normally excreted through urine. Oxalate is also produced by your body as a byproduct of oxalic acid metabolism, especially from vitamin C and the amino acids glycine and hydroxyproline. Oxalic acid is used in minuscule quantities in all cells for the production of uracil, a nucleotide found in RNA^[2].

Health problems can occur with long-term excessive consumption of high oxalate foods, especially in sensitive individuals who absorb higher amounts, produce more, or battle to excrete oxalate. Once in the body, oxalate can go on to further bind to bone minerals, contribute towards kidney stone formation, as well as accumulate in the kidneys, other organs and tissues.

How Oxalate Affects Your Health

The most common problems attributed to oxalates are mineral depletion and kidney stone formation.

Mineral Depletion. Oxalate can interfere with the absorption of minerals like calcium, iron, magnesium, and zinc from the diet. This can lead to mineral deficiency and exacerbate related health problems, such as:

• Osteoporosis
• Anemia
• Muscle cramps
• Immune dysfunction

Kidney Stones and Damage. Oxalate can also contribute to kidney stone formation by binding with calcium in the urine and forming crystals. Calcium oxalate kidney stones are the most prevalent type of kidney stone, accounting for up to 80% of all cases.^[3] Kidney stones can cause obstruction, severe pain, nausea, vomiting, blood in the urine, fever, chills, and urinary tract infections. If left untreated, kidney stones can cause kidney damage and lead to chronic kidney disease or kidney failure. Prior to kidney stone formation, oxalate excretion via the kidneys may irritate or damage them. The enzymatic breakdown of oxalate can also increase protein production in the body, which can indirectly contribute to kidney damage in the long run.

Gut Irritation. High quantities of dietary oxalates can irritate the gut and cause bloating, especially in those sensitive to oxalate or who have a weak digestive system. Oxalates are also toxic to certain kinds of beneficial gut bacteria, such as bifidobacteria.^[4]

Other Health Conditions Arising from Oxalate Overload

Oxalate can also cause other health problems, such as:

• Hyperoxalemia: This is a condition where oxalate builds up in the blood. This can happen when the kidneys are not able to filter out enough oxalate or when there is excessive oxalate production or absorption from the diet or the gut. Hyperoxalemia can cause symptoms such as fatigue, weakness, nausea, vomiting, and confusion.
• Hyperoxalosis: This is a rare condition where oxalates deposit in various tissues and organs, such as the eyes, bones, muscles, skin, blood vessels, heart, and brain. It can cause vision loss, bone and joint pain, muscle stiffness, skin ulcers, anemia, heart failure, and neurological problems. It usually occurs after long-term hyperoxalemia or if the kidneys struggle to function properly.
• Vulvodynia: This is a chronic pain syndrome of the vulva, the inner skin around the opening of the vagina. Symptoms include burning, itching, soreness, stinging, or throbbing sensations. Some cases of vulvodynia may be associated with high levels of oxalates in the urine. However, more research is required to confirm these observations.
• Autism: This is a developmental disorder that affects communication and behavior. Some studies have suggested that oxalates may play a role in autism by affecting brain function and metabolism.^[5]
• Cancer: There are mixed studies with respect to oxalates and carcinogenesis. Oxalates may promote breast cancer^[6] and tumor metastasis^[7]. Other studies suggest that it may encourage tumor cell death through binding to calcium^[8].

Factors that Increase Oxalate Uptake, Synthesis and Accumulation

Not everyone is sensitive towards oxalates, although consuming a very high amount for a prolonged period of time is not recommended. One’s sensitivity towards oxalate depends on genetics, the state of the gut and microbiome, nutritional status, as well as the health and functioning of the liver and kidneys.

Some individuals are genetically susceptible to forming kidney stones due to mutations or deletions in the gene responsible for its elimination: SLC26A1. This gene regulates the expression of proteins that promote the clearance of oxalates and other substances, such as sulfate, chloride, bicarbonate, formate, and other anions.^[9]

Those genetically susceptible are likely to exhibit high oxalate content in their urine (hyperoxaluria) and be more sensitive to dietary oxalates, having a weaker microbiome and absorbing more on average. Those who form kidney stones have been shown to absorb up to 1.9% more oxalates from their diet^[10].

Other factors that can influence the risk for kidney stones and hyperoxalemia include:

• Lactic acid buildup or a diet high in lactate, which promotes the production of glyoxylate, a precursor to oxalate. Extreme buildup or acidosis is known to promote oxaluria and kidney damage^[11]. Muscle lactic acid can increase due to overconsumption of lacto-fermented foods, a lack of physical activity, or prolonged starvation.
• High vitamin C intake. Excess vitamin C can metabolize into oxalate either directly or indirectly, although it can also promote the excretion of oxalate.
• Inflammation or increased oxidation, which enhances the bodily production of oxalate.
• Nutritional deficiencies, including those of vitamin B6, calcium, magnesium, citrate and thiamine.^[12] A diet low in antioxidant nutrients may also contribute by promoting inflammation and oxalate formation in the body.
• A gut barrier breach or lower gut microbe diversity, which can increase dietary oxalate absorption as well as lower its degradation and excretion. In a healthy gut, lactobacilli may degrade oxalate by up to 68%, while oxalobacter may degrade 30-50%. Lower amounts of these may contribute towards increased absorption.
• Low dietary calcium or citrate. These are the number one nutrients that can bind to oxalate and enhance their elimination. Low dietary levels are associated with higher oxalate absorption.

How Much Oxalate Per Day is Healthy?

There is no clear answer as to how much oxalate per day is unhealthy for those who aren’t at risk of kidney stones.

It has been theorized that the body can excrete 25-30 mg of oxalate through urine per day. The average healthy person is thought to hold roughly 52 mg of oxalate in their bodies at any given time.^[13] Studies assessing oxalate absorption estimate that we absorb 2-20% of ingested oxalates if we consume 800 mg of calcium per day^[14].

This means that we can probably get away with consuming between 125-1000 mg per day and that those who can tolerate the higher end are likely to have healthier guts, consume a lot more calcium, and have no genetic issues regarding oxalate metabolism. It is worth mentioning that an excessively high daily intake of oxalate might induce sensitivity to them over time, yet many high oxalate foods are extremely beneficial for health and should not be entirely avoided unless one is highly sensitive.

Healthy individuals may want to avoid foods high in oxalate if unwell, when dehydrated, or when having an upset stomach.

Preventing Calcium Oxalate Stones and Body Oxalate Accumulation

For those sensitive to oxalate or at a high risk of kidney stones or problems, it can be a good idea to limit oxalate intake and lower its production in the body.

Those who are already generally healthy and who suffer from the following conditions may also benefit from moderating their oxalate intake:

• Nutritional deficiencies
• IBS/IBD^[15]
• Allergies or food sensitivities
• Cardiovascular conditions like atherosclerosis^[16]
• Anemia
• Bone problems, including osteoporosis

Here are some tips to help you prevent calcium oxalate stones:

Drink Enough Water

Water is essential for keeping your urine diluted and preventing crystal formation. You should drink at least 2 liters (8 cups) of water per day, or more if you sweat a lot or live in a hot climate locale. You can also drink other fluids, such as herbal teas, fruit juices, and soups, yet avoid beverages high in oxalates or that increase body oxalate, such as black tea, cola, and beer.

Consume Adequate Calcium

Calcium is vital for your bones, teeth, and muscles, but it also helps prevent kidney stones by binding with oxalate in your gut and reducing its absorption into your bloodstream. You should aim for about 1 gram (1000 mg) of calcium daily from food sources or supplements^[17]. Some beneficial sources of calcium include dairy products (such as milk, cheese, and yogurt), legumes, low-oxalate nuts, green leafy vegetables (such as kale and broccoli), tofu, and fish.

Reduce Salt Intake

Salt can increase your urine calcium and uric acid levels, which can promote stone formation. You should limit your salt intake to less than 2 grams (2000 mg) per day^[18] or 1.5 gram (1500 mg) if you have high blood pressure or kidney disease^[19]. You can reduce your salt intake by avoiding processed foods (such as canned soups, frozen meals, and snacks), using herbs and spices instead of salt to flavor your food, and reading food labels to check the sodium content.

Reduce Animal Protein Intake

Animal protein can also increase your urine calcium and uric acid levels, which can promote stone formation. You should limit your consumption of animal protein to less than 0.8 grams per kilogram^[20] of body weight per day or approximately 56 grams (2 ounces) for a 70 kg (154 lb) person. You can reduce your animal protein intake by opting for lean meats (such as chicken, turkey, and fish), eating more plant-based proteins (such as beans, lentils, and soy products), and having meatless meals at least once or twice a week.

Regular Exercise

As lactic acid buildup contributes to body oxalate production, regular exercise is important for preventing kidney stones and helping keep oxalates in check. Exercise may have additional benefits, such as regulating inflammation, blood glucose, and overall metabolism, which may serve to keep oxalate production to a minimum as well. Intermittent fasting might pose similar benefits and help to lower body oxalate concentrations.

Do Not Consume Too Much Sugar or Fructose

Both refined sugar and fructose can negatively affect kidney and liver function, lower one’s ability to handle oxalates, and may even increase body oxalate production through different means. Fruits are naturally low in oxalates yet high in fructose. Consuming low-glycemic fruits within the context of a balanced diet can help keep oxalates in balance. Citrus fruits have the added bonus of being high in citric acid and offering modest amounts of calcium.

Increase Citrate Intake

Citrate is a natural substance that can inhibit crystal formation by binding with calcium and oxalate in the urine^[21]. You can increase your citrate intake by consuming more fruits and vegetables, especially citrus fruits (such as oranges, lemons, and grapefruits), melons (such as watermelon and cantaloupe), and berries (such as strawberries and blueberries). You can also take citrate supplements, such as potassium citrate or sodium citrate, under the guidance of your doctor.

Probiotics and Prebiotics

Consuming small quantities of probiotics, lacto-fermented foods, and vinegar may be able to reduce oxalate absorption as well as enhance their metabolism and excretion once absorbed. If too high, lacto-ferments may increase lactic acid buildup and enhance oxalate formation, yet in low amounts, they can help to repopulate the gut with oxalate-degrading lactic acid bacteria. Vinegar is associated with a lower risk of kidney stone formation, possibly due to regulating oxalate absorption, promoting citrate production and oxalate excretion^[22].

Avoid or Limit Foods High in Oxalate

Oxalates are the main culprit for causing kidney stones, so you should avoid or limit foods that are high in oxalates. These contain more than 50 mg per serving and sometimes even between 100-1000 mg. Some people may need to restrict their intake of moderate oxalate foods as well.

Foods high in oxalate are almost always leafy greens relative to their serving sizes. Herbs, teas, spices, and some grains may also contain large quantities, yet as they are not consumed in significant amounts, they don’t often trouble those who opt for a balanced diet.

High oxalate foods relative to their serving sizes include:

• Star fruit, which can comprise close to 5000-9500 mg per 100 g (1 medium fruit is roughly 90 g)
• Rhubarb, which can contain 1336 mg per cup raw, 260-660 mg when cooked.
• Spinach, which can contain up to 755 mg per half cup cooked.
• Beet leaves, containing 610-2300 mg per 100 g raw
• Beets, containing anywhere between 100-700 mg, raw or cooked, depending on the type
• Plantain banana, containing up to 534 mg per 100 g (one weighs up to 270 g)
• Cacao or cocoa powder, which can contain between 300-1470 mg per 100 g
• Almonds, 122-407.3 mg per 100 g raw

You can find a list of foods that are high, moderate, or low in oxalates online^[23] or through your doctor or dietitian.

Following a Low Oxalate Diet

A low oxalate diet is a type of diet that can help reduce your oxalate intake to prevent kidney stones and hyperoxalemia. Following a low oxalate diet involves avoiding foods that are high in oxalates (more than 50 mg per serving) and choosing low or moderate sources instead. Low oxalate foods are generally less than 10 mg per serving, while moderate oxalate foods contain 10-50 mg.

The amount of oxalate that you need to limit depends on several factors, such as your medical history, kidney function, urine output, calcium intake, and genetic predisposition. Generally, a low oxalate diet is considered less than 100 mg per day, though some people may need to restrict it to less than 50 mg per day. It is essential to consult your doctor or a dietitian before making dietary changes, especially in case of underlying health conditions.

Here are some examples of foods that are low or moderate in oxalates (less than 10 mg per serving):

• Vegetables: Asparagus, broccoli, cauliflower, celery, cucumber, lettuce, onion, green beans, carrots, corn, peas, zucchini, etc.
• Fruits: Apple, banana, grapefruit, kiwi, mango, orange, peach, pear, pineapple, etc.
• Grains: Rice, oats, quinoa, barley, buckwheat, etc.
• Meat and poultry: Chicken, turkey, beef, pork, lamb, etc.
• Eggs: Whole eggs or egg whites.
• Dairy products: Milk, cheese, yogurt, butter, cream, etc.
• Nuts and seeds: Walnuts, pecans, sunflower seeds, pumpkin seeds, etc.
• Legumes: Lentils, chickpeas, black beans, kidney beans, etc.

Here are some tips on how to reduce the oxalate content of foods:

• Soak and cook certain vegetables and legumes (such as potatoes and beans) for at least 10 mins before eating them. This can reduce the oxalate content by up to 50%.
• Peel fruits and vegetables before eating them. This can reduce the oxalate content by up to 30%.
• Discard the water used for boiling or steaming foods instead of consuming them with or incorporating them into the meal. This can reduce the oxalate content by up to 80%.

Conclusion

Oxalate is a natural substance that can pose drawbacks for your health, depending on the amount consumed and how well it is balanced with other nutrients. The main problems associated with a high oxalate intake include lower mineral absorption, an increased risk of kidney stone formation, and other health problems due to oxalate accumulation. Those with weaker digestive systems, who consume less calcium daily, who have metabolic problems or relevant gene mutations might be more sensitive due to absorbing more oxalate or struggle to excrete it.

You can prevent kidney stones and improve your health by following some dietary and lifestyle strategies that support oxalate metabolism. These include drinking enough water, getting enough calcium, reducing your salt and animal protein intake, increasing your citrate intake, and avoiding or limiting foods that are high in oxalates.

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