Let’s Talk About Oxalates!
- Christine Daecher, DO
- Aug 28, 2024
- 4 min read
Updated: Dec 3, 2024
Oxalates are found in the diet and are produced by the body. Read on to find out their value or lack thereof.
For this review, oxalic acid should be considered the same as oxalates.
Oxalates and Kidney Stones
There are three main components of kidney stones: calcium, oxalate, and uric acid. (Rarely cystine, ammonium acid urate, xanthine, dihydroxyadenine, and various rare precipitation of medications are involved.) The calcium oxalate stone is by far the most common type of kidney stone and accounts for at least 75% of kidney stones. The bad news is that olaxic acid can form crystals within our body, specifically in the kidneys. Once a crystal forms, it can precipitate further crystal formation leading to stones.
Oxalic acid is a waste product produced by the breakdown of glycine and hydroxyproline and through the glyoxalate pathway. A rare genetic defect that some carry results in very high oxalate levels in the urine or primary hyperoxaluria. Unfortunately, anyone with this mutation suffers from frequent and severe calcium oxalate kidney stones and also has oxalate deposits in the bones, joints, and other tissues. People who have this condition have very high levels of production and excretion of oxalates, around 100 to 600 mg per day. Normally, the body produces only 10-30mg per day. As you read on, try to remember this number, 100 to 600 mg per day.
Over the years, I have met patients who've had a history of recurrent kidney stones. As we talk, it turns out many of them were drinking "green smoothies" when the stones suddenly started forming. Most of them are drinking smoothies multiple times a day. These people continued to drink green smoothies and continued to have many kidney back-to-back stones. I ask if the stones are calcium oxalate. The answer is yes. I ask if they were eating a lot of spinach. Another, yes.
Oxalic Acid in Plants (and Fungi)
Plants use oxalic acid during photosynthesis. In plants and fungi, it serves as a chelating compound to help regulate the amount of calcium, magnesium, and zinc within plant cells. Oxalates form needle-like crystals that are pointed at both ends. They're also used as a deck fence weapon against predators.
There are several foods that are very high in oxalate and produce very high levels of oxalate in your urine in the 2-4 hours after ingestion. These levels match those of people with the genetic defect, primary hyperoxaluria. For every 100g serving of almonds, you will acquire 120 mg of oxalates; rice bran 281 mg, sorrel 300 mg, rhubarb stalks 541 mg, spinach 755 mg, and turmeric powder, a whopping 2,190 mg! Foods with oxalate amounts between 40-100 mg include sesame seeds, baked potato, yams, soy, navy beans, beets, cocoa, cornmeal, black tea, green tea, star, fruit, nuts, peanuts, mushrooms, okra, french fries, cashew, shredded wheat, raspberry, and barley flour. From above, I wanted you to remember the number of 100 to 600 mg per day. This is in very abnormally high amounts of production of oxalates. Also, recall that the normal amount is 10 to 30 mg per day.
About rhubarb...eating rhubarb leaves causes fatal oxalic acid poisoning due to severely high levels of oxalic acid, which binds to calcium and causes deadly low levels of calcium. Oxalate poisoning is the mechanism of many plant poisonings.
Oxalates and Other Conditions
Not only do oxalates have the ability to cause kidney stones, but they also have the ability to cause kidney disease or nephropathy. People who have chronic kidney disease and gastrointestinal malabsorption are at a much higher risk. Since the body gets rid of oxalates in the urine, imagine the damage high amounts of these little needles do going through the delicate renal tubules (kidney filtration unit).
Oxalate dumping may occur in someone who abruptly stops consuming oxalates. When this occurs, a person may experience many unpleasant symptoms for a few days to weeks.
For many people, taking supplemental vitamin C may benefit them. The bad news is that for some people, this results in significant increases in oxalates. Vitamin C is partially broken down into oxalate and excreted. It's probably best not to overdo it with vitamin C supplements, especially since it's water-soluble, and anything extra is peed out.
Oxalate crystals are also found in breast tissue, including pre-cancerous lobular carcinoma in situ. It appears oxalates also induce cancer-promoting c-fos in breast tissue. Studies in mice have shown that directly injecting oxalates into mamillary fat in mice produces tumors.1
Oxalate arthropathy may be primary in a person with primary hyperoxaluria (the genetic condition discussed above) or secondary in a person with secondary hyperoxaluria (chronic kidney disease and gastrointestinal malabsorption). Oxalates have been shown to accumulate and deposit in the bones, joints, heart, retinas, and skin2.
Lowering Dietary Oxalates
A diet low in oxalates may provide other benefits. Some people without clear pathologic tissue disease report less breast pain, dyspareunia, lower urinary tract symptoms, and musculoskeletal pain when they cut oxalates from their diet. This makes sense since oxalate is a waste product that has no function in our bodies and tends to form a needle-like crystal.
Tea drinkers should avoid matcha. One serving of matcha is 2-4 grams and each gram has approximately 17 mg of oxalates.
Tea drinkers should avoid iced tea. Iced tea is usually a black tea. Less than 1/2 cup of it contains 50-100 mg of oxalates. (If adding sugar, this is further risk for kidney stones.)
Green smoothies should be avoided.
Avoid or limit the highest oxalate-containing foods.
Occasionally, Google high oxalate foods or cross-check a particular food.
The Oxalosis and Hyperoxaluria Foundation has created an easy-to-use spreadsheet for looking up foods. (I find it easiest to use the "find" function of command F or Control F.)
1 Castellaro AM, Tonda A, Cejas HH, Ferreyra H, Caputto BL, Pucci OA, Gil GA. Oxalate induces breast cancer. BMC Cancer. 2015 Oct 22;15:761. doi: 10.1186/s12885-015-1747-2. PMID: 26493452; PMCID: PMC4618885.
2 Lorenz EC, Michet CJ, Milliner DS, Lieske JC. Update on oxalate crystal disease. Curr Rheumatol Rep. 2013 Jul;15(7):340. doi: 10.1007/s11926-013-0340-4. PMID: 23666469; PMCID: PMC3710657.
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