Oxalates in food are either soluble or insoluble. Insoluble oxalate is bound to another molecule that makes it much harder to absorb; normally calcium but also sometimes magnesium. Calcium supplements are often recommended for oxalate kidney stone patients to bind with oxalate so it can be excreted.
People who tend to form kidney stones or who suffer from osteoporosis may benefit from a low-oxalate diet. However, healthy people trying to stay healthy do NOT need to avoid mushrooms like Chaga and other high oxalate foods including spinach, beet greens, and almonds. It is simply not a nutrient of concern for most people.(1)
Insoluble oxalates (calcium oxalate, magnesium oxalate and iron oxalate) are not absorbed in the digestive system and pass harmlessly in the feces. However, soluble oxalates (potassium oxalate and sodium oxalate), release free oxalate anions which pass in to the blood stream. Free oxalate will bind with any free calcium to produce calcium oxalate crystals potentially resulting in gout, kidney stones, and physical damage to the kidneys while depleting calcium needed for strong bones, etc.(2)
Oxalates in cultivated mushrooms
Considering only soluble oxalates, we learn that most cultivated mushroom species, not only are total oxalates low, but 90% are insoluble. In a study by Nile and Park they examined oxalate levels in twenty species of popular wild edible mushrooms.(4) All had very low to moderate oxalate levels.
Cultivated Lentinula edodes (Shitake mushroom), has moderately high total oxalates (just over 1,000 mg/kg DM) but 99% of the oxalates are insoluble, and thus harmless to ingest. Cultivated Pleurotus ostreatus (oyster mushroom), in contrast, had moderate oxalate levels, but 90% were in the soluble form, making it a moderate over-all oxalate risk, a risk level of concern to people with serious gout or serious kidney stone problems, but no worse than foods like chocolate, almonds, cereal grains.
Most cultivated mushroom species, not only are total oxalates low, but 90% are insoluble.
They found no soluble oxalates in Hericium erinaceus (Lions mane mushroom), Sparassis crispa (cauliflower fungus), Boletus edulis (porcini mushroom, and Ganoderma lucidum (Reishi mushroom). The highest levels of soluble oxalate were found in Phellinus floriada (65 mg/kg DM) and in Morchella conica (morels) (60 mg/kg DM) where the oxalate risk would be rated as moderate.(3)
Sources report either that Chaga has high oxalate levels or extremely high levels, but give no values.
Oxalates in Chaga Mushroom
A NAMA toxicology study reported on the oxalate levels in Chaga in a sample from Russia, a sample from Finland and a sample from Thailand.(5) They performed a hot water extract of each sample (to determine the soluble oxalate levels), and followed differences between the three samples.
The Russian material yielded 1 gram of extract (from 25 g of powdered Chaga) containing 97.6 mg soluble oxalic acid and 24 mg of insoluble oxalic acid which equates to 3,904 mg soluble oxalates/kg DM and 960 mg/kg DM insoluble oxalates/kg DM in Russian Chaga. For the Russian material, 97% of the organic acids extracted were soluble and insoluble oxalates.
The material from Finland yielded 2.4 g of extract containing 55.62 mg/g of soluble oxalate and 9.5 mg/g of insoluble oxalates, which equates to 5,340 mg/kg DM of soluble oxalates and 910 mg/kg DM insoluble oxalates in material from Finland. In the Finnish material, 84% of the organic acids were oxalates and 16% was para-hydroxybenzoic acid.
In the material from Thailand, a region well outside of the known circumboreal range of Chaga, oxalates comprised only 25% of the organic acids, with 1,710 mg/kg DM soluble oxalates and 350 mg/kg DM insoluble oxalates. The main organic acid in the material from Thailand was para-hydroxybenzoic acid (73.6%) with 0.3% gallic acid and 1.1% protocatechuic acid.
Wild Russian Chaga - 97.6% soluble oxalate
Wild Chaga from Finland - 55.62% soluble oxalate
Wild Chaga from Thailand - 25% soluble oxalate
There are no studies to date on oxalates found in wild Chaga from North America - (Canada & USA). However, as Canadian Chaga is within similar circumboreal regions one could estimate that it too would have similar oxalate levels to that of Chaga from Russia.
In all of these samples, oxalate levels were far higher than those found in edible mushrooms and are comparable to levels in foods like almonds, peanuts, cereal grains and chocolate that are rated as very high in oxalates. The oxalate levels are much lower than oxalate levels found in foods with extremely high oxalate levels like spinach, rhubarb and beet greens.
Oxalate in wild Chaga vs. cultivated Chaga
Cultivated Chaga is very different from wild harvested Chaga since it lacks the betulin produced by the tree, and also lacks betulinic acid and phytosterols. Consequently, one would expect a different suite of soluble or insoluble oxalates and effects from cultivated Chaga vs wild Chaga since the chemistry is different.
Oxalate levels in cultivated Chaga appear to be unstudied.
The high soluble oxalate levels in wild-harvested Chaga should make people with osteoporosis think twice before using Chaga since oxalates chelate calcium, zinc and other metals, stripping them from the body. Oxalate levels in cultivated Chaga appear to be unstudied.
Is chaga Safe?
Until more hard data is available one should consider wild Chaga among foods high in oxalates. As such if you suffer from kidney stones then you should limit your consumption of chaga and other foods that contain high oxalate levels. Another reason why it is important to avoid over consumption of chaga and limit your daily dose of Chaga mushroom tea to 1-2 6oz cups or 3.6g of dried per day.
An interesting paradym is the fact that wild chaga contains very high levels of calcium, magnesium, iron and other minerals. Even as soluble oxalate chelate them from the body wild Chaga mushroom offers them in abundance at the same time.
1.Oxalates in Chaga – A Potential Health Threat By Michael W. Beug, Chair NAMA Toxicology Committee
2. Savage GP, Nilzen V, Österberg K, Vanhanen L. 2001. “Soluble and insoluble oxalate content of mushrooms”. International Journal of Food Sciences and Nutrition 53: 293- 296.
4. Nile SH and Park SW. 2014. “Bioavailability Analysis of Oxalate and Mineral Content in Selected Edible Mushrooms” Journal Nutritional Disorders and Therapy
4(1):138 doi:10.4172/2161-0509.1000138 5. Glamočlija J, Ćirić A, Nikolić M, Fernandes Â, Barros L, Calhelha, R, C.F.R. Ferreira I, Soković M, J.L.D. van Griensven L. 2015. “Chemical characterization and biological activity of Chaga (Inonotus obliquus), a medicinal ‘mushroom’” Journal of Ethnopharmacology 162: 323-332.