Spinach, beetroot, soy products, dates, seeds, raspberries are an important sources of plant food that supply us with many essential nutrients. Majority of us include them in our diet regularly. For example, spinach offers a trifecta of ingredients for enhancing eye health: beta-carotene, lutein, and vitamin E. This superfood is recommended to offer to growing children to ensure optimal eye health. However, what we do not know is that these nutritious plant foods are actually high in oxalates.
Oxalate is a cause for health concern
Oxalates are naturally-occuring substance in plants that regulates the mineral content in their internal environment to ward off predators. These oxalates play a supportive role in metabolism in the plant itself but is considered a uremic toxin for human health especially individuals with kidney issues (Pfau et al., 2021).
Similar to phytates, oxalate is an anti-nutrient. This would mean that oxalates bind to minerals (sodium, potassium, iron, and magnesium and calcium) in our gut and prevent these minerals from being absorbed for our growth and bodily functions, particularly when combined with fiber.
This can in turn lead to malnutrition. Oxalate commonly binds with calcium to form calcium oxalate, which is then excreted in the feces. This binding reduces how much calcium can be absorbed for our bodies use. For example, spinach contains both calcium and oxalate, calcium oxalate binding will hinder calcium absorption into our bodies from spinach. Calcium absorption into our bodies will not be hindered if we consume milk due to absence of oxalate in milk.
Does it mean that we have to eliminate spinach, beets and even soy products?
Defintiely not. Unless one has a history of kidney stones and is instructed by doctor. It is however encouraged to eat a whole variety of foods, including fermented foods, in balance to ensure the intake of wholesome nutrients.
Oxalates that comes from foods make up about 20 to 40% of the total oxalate in our body. The remaining comes from our bodies that make oxalates internally via (1) creating them from amino acids in our liver; (2) taking vitamin C and transforming it into oxalate; and (3) having our red blood cells making oxalates from glyoxylate.
The formation of kidney stones
As mentioned above, oxalate commonly bind to calcium forming calcium oxalate crystals being the most common form of kidneys tones. In normal cases, bound oxalate calcium crystals in intestines will leave our bodies in faeces. In some cases when there is an excess of oxalate in our gut, either due to overconsumption of oxalate-rich foods or medical conditions that leads to an incapability to degrade oxalate efficiently, these excess oxalate can be reabsorbed back into our bloodstream and enter our kidneys. In our kidneys, when the concentration of calcium gets too high, they crystalize to form calcium oxalate stones, also known as kidney stones.
Individuals with medical conditions (e.g., dent disease, hyperparathyroidism and IBD) could pose a higher risk for kidney stones or/and occurrence of hyperoxaluria
Sensibly, the way to prevent kidney stones is to prevent excessive oxalates from exiting the gut lumen or/and reducing oxalate level in our bodies. However, eliminating oxalate-rich foods entirely is never a solution for healthy individuals as these foods provide precious vitamins and minerals in order for our body to function optimally.
In this blog, we will be sharing on how our lifestyle can make a huge impact in our overall kidney health and the crucial role played by milk kefir in regulating the amount of oxalate in our bodies.
1. Adequate water consumption and reduce salt intake
By ensuring sufficient water intake, it is shown to reduce the risk of kidney stone formation. Low fluid intake can lead to decreased urine output and slowed urine flow, both factors will increase the risk of stone formation. Children should consume an approximate of 4 to 8 cups of water or/and milk per day.
2. Avoid taking a Vitamin C supplement but obtain from real food sources
Because ingested Vitamin C is partly converted to oxalate and excreted in the urine, any excess consumed will be excreted by our kidneys via urine which can potentially increase the risk of calcium oxalate stone formation (Ferraro et al., 2016). Swedish researchers detail a connection between kidney stone formation and use of vitamin C supplements among more than 23,000 Swedish men. It was discovered that taking vitamin C supplements resulted in twice as likely to develop kidney stones for them.
The recommended dietary allowance for vitamin C is 90 mg/day for adult men, 75 mg/day for adult women, 15-75 mg/day for children depending on age. To give you an idea of how much to consume, an average orange will contain 70mg of vitamin C.
3. Consume citrate foods
Orange, lemon and lime are citrate fruits that do not solely contain Vitamin C. They naturally contain citrate (citric acid) as well. Despite containing vitamin C, the chances of Vitamin C overaccumulation is very unlikely with real fruits. Supplementation supply an average of 10 times more vitamin C than what real fruits provide. These citrate fruits helps to prevent kidney stones via (1) citrate binds with calcium in urine, thereby reduces the concentration of urine, (2) citrate binds to calcium oxalate crystals (a.k.a stones) in whole to prevent further crystal growth. Consuming just 120ml of lemon or orange juice per day has been shown to significantly increase urine citrate levels without increasing oxalate levels (Seltzer et al., 1996).
3. Take calcium rich foods together with plant food/fruits
Despite calcium oxalate crystals ibeing the most common cause of kidney stones, this does not mean that we should stop taking foods with calcium. In fact, low calcium intake has been linked with a higher risk of developing kidney stones due to the lack of calcium binding to oxalates in the intestinal tract and passing these oxalates as stools (Gul & Monga, 2014). The free unbound oxalates eventually exits the intestine and absorb back into our blood system which finally reaches our kidney, causing an increase in urinary oxalate production.
TGF strawberry, berries baby and beetroot kefir smoothie will be an optimal choice for individuals who had kidney stones, at a high risk for kidney stones and prevention of kidney stones as calcium (in the form of dairy) is consumed together with oxalate-rich foods such as beets and berries.
It is important to note that adequate calcium intake does not mean high calcium intake. Consumption of more than what our bodies need can lead to an increased risk of kidney stones. Dietary calcium (whether from dairy or non-daory sources) is shown to be a likely protective factor against kidney stone formation (Taylor & Curhan, 2013). This is due to the fact that it is unlikely to overconsume calcium through foods.
4. Oxalate-degration gut microbes
We have talked about how we can make changes to our diet and lifestyle to prevent the formation of kidney stones. Another strategy to prevent hyperoxaluria is to degrade oxalates. Humans lack the enzymes to break down oxalates but there are specific bacterial strains and species in our gut who are well able to perform this role. It is shown that such oxalate-degrading bacteria in the gut are able to decrease oxalate by 40% (Karamad et al., 2022). The absence of these gut bacteria increases the risk of kidney stones formation.
Oxalobacter formigenes is a well-known gut bacteria that degrades oxalate efficiently due to oxalate as its only source of energy. Although it is unknown if Oxalobacter formigenes is present in fermented foods, it is believed by researchers that high levels of kefir consumption leads to an elevated level of Oxalobacter formigenes.
Scientist have also isolated certain lactic-acid bacteria from fermented dairy which can also perform oxalate degradation effectively. In a study in 2021, 5 strains of Lactobacillus fermentum and 2 strains of Lactobacillus gastricus isolated from dairy products were identified as having strong oxalate degradation abilities (Soliman et al., 2021). In another study, Turroni et al. (2010) reported that maximum oxalate degradation ability was measured in the isolates of Lactobacillus salivarius AB11 (62.59%), Lactobacillus fermentum TY12 (58.3%) and five strains of Lactobacillus fermentum.
Gut microbiota play an important role in gut-kidney physio-pathology. Inhibiting urinary stone disease by maintaining healthy oxalate homeostasis can be achieved by a multi-species bacterial network (Miller et al., 2019).
Fermented foods that harbours the widest biodiversity, especially milk kefir, not only prevent malabsorption of nutrients, ensure immune homeostasis ("fight" and "calm down" appropriately), but also aids in oxalate degradation that keeps our kidneys healthy. Needless to say, gut microbes is also essential in keeping our other vital organs such as brain and lungs functioning optimally. Dairy based food matrix has been found to be arguably the best probiotic carrier with for sustaining the therapeutic effects in humans (Ranadheera et al., 2018). Therefore, we always say milk kefir is an essential and never a choice for a healthy lifestyle.
Curhan GC, Willett WC, Speizer FE, Spiegelman D, Stampfer MJ. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women. Ann Intern Med. 1997;126:497–504.
Karamad, D., KHosravi-Darani, K., Mousavi-Khaneghah, A., & Miller, A. (2022). Probiotic oxalate-degrading bacteria: New insight of environmental variables and expression of the OXC and FRC genes on oxalate degradation activity. https://doi.org/10.20944/preprints202207.0458.v1.
Miller, A. W., Choy, D., Penniston, K. L., & Lange, D. (2019). Inhibition of urinary stone disease by a multi-species bacterial network ensures healthy oxalate homeostasis. Kidney International, 96(1), 180–188. https://doi.org/10.1016/j.kint.2019.02.012.
Pfau, A., Ermer, T., Coca, S. G., Tio, M. C., Genser, B., Reichel, M., Finkelstein, F. O., März, W., Wanner, C., Waikar, S. S., Eckardt, K.-U., Aronson, P. S., Drechsler, C., & Knauf, F. (2021). High oxalate concentrations correlate with increased risk for sudden cardiac death in dialysis patients. Journal of the American Society of Nephrology, 32(9), 2375–2385. https://doi.org/10.1681/asn.2020121793.
Ranadheera, C. S., Naumovski, N., & Ajlouni, S. (2018). Non-bovine milk products as emerging probiotic carriers: Recent developments and Innovations. Current Opinion in Food Science, 22, 109–114. https://doi.org/10.1016/j.cofs.2018.02.010.
Seltzer MA, Low RK, McDonald M, Shami GS, Stoller ML. Dietary manipulation with lemonade to treat hypocitraturic calcium nephrolithiasis. J Urol. 1996;156:907–909.
Soliman, N. R., Effat, B. A., Mehanna, N. S., Tawfik, N. F., & Ibrahim, M. K. (2021). Activity of probiotics from food origin for oxalate degradation. Archives of Microbiology, 203(8), 5017–5028. https://doi.org/10.1007/s00203-021-02484-3.
Taylor, E. N., & Curhan, G. C. (2013). Dietary calcium from dairy and nondairy sources, and risk of symptomatic kidney stones. Journal of Urology, 190(4), 1255–1259. https://doi.org/10.1016/j.juro.2013.03.074.
Turroni S, Bendazzoli C, Samuele C, Dipalo F, Candela M, Vitali B, Gotti R , Brigidi P (2010) Oxalate-Degrading Activity in Bifidobacterium animalis subsp. lactis: Impact of Acidic Conditions on the Transcriptional Levels of the Oxalyl Coenzyme A (CoA) Decarboxylase and Formyl-CoA Transferase Genes. Applied and Environmental Microbiology76: 5609-5620.