When I first learned about the association of oxalates in food with the development of kidney stones, chronic pain, and other health conditions, I was curious. I had eaten foods that are high in oxalates for years, particularly spinach, sweet potatoes, and chard, without experiencing any apparent symptoms.
Why is it that some experience health issues linked to high oxalate foods while others do not? Is it genetic differences? Hydration status? Overall diet and lifestyle?
When I started digging into the research I realized there is more to the story.
Oxalate-digesting bacteria
The first clue I uncovered was the research on a bacterium called Oxalobacter formigenes which produces an enzyme that is able to break down oxalates in the body. The presence or absence of these particular strains of bacteria make a significant difference in how our bodies respond to oxalate-containing foods. When there is a healthy population of this bacterium, oxalates are broken down before they can accumulate in sufficient quantity to form kidney stones.
Given that antibiotics tend to be prescribed recklessly in conventional Western medicine, I wanted to see if any studies had been done that look at associations between antibiotic usage and the prevalence of kidney stones…
Antibiotics, Oxalate-degrading bacteria, and Kidney stones
A review entitled “The Use of Antibiotics and Risk of Kidney Stones” was particularly interesting to me, as it highlighted several studies that demonstrated a link between antibiotic usage and subsequent risk of kidney stone formation.
While no claims were made that die-off of Oxalobacter formigenes was the sole cause of the kidney stones (other bacteria can also digest oxalates), the correlations between the presence of Oxalobacter formigenes in the gut, recent antibiotic usage, and prevalence of kidney stones were very strong.
Interestingly, the population of Oxalobacter formigenes was greater in those who consume more oxalate-containing foods, indicating that the gut microbiome is very responsive to one’s diet. What is too much oxalate for one individual may not cause an issue for someone whose gut is colonized with O. formigenes to a greater degree.
Fermented food and Oxalate levels
After learning that bacteria residing in our gut can break down oxalates, it seemed logical that this could also occur when foods are fermented. Sure enough, I came across an article titled “Nutrient and antinutrient profiles of raw and fermented cocoa beans”.
This study examined the effect of fermentation on oxalate levels in cocoa beans over a 12-day period in three-day intervals. After 12 days the insoluble oxalate content was reduced by 64%. Apparently, six days of fermentation is the standard practice in the area of Nigeria where the study was done, as it is believed to be the ideal duration for optimal flavor. The six-day fermentation period resulted in a 19% reduction in oxalates.
Another study, “Effect of Kimchi Fermentation on Oxalate Levels in Silver Beet (Beta vulgaris var. cicla)” demonstrated that a five-day fermentation period reduced insoluble oxalates by 70.4%. This study concluded that the reduction in oxalates was due to a lowering of pH that causes insoluble oxalate to become soluble oxalate, which then can be degraded by a bacterial strain called Lactobacillus plantarum.
In other words the bacteria are trying to help us out by making our food taste better and become more easily digested. Let ‘em cook!
Who should avoid high-oxalate foods?
I’m sure many people have improved their health by following diets that largely eliminate oxalate-containing foods such as the carnivore diet, but I think the success of these diets is primarily a result of eliminating highly processed junk foods that people tend to consume in large quantities (white bread, pasta, soda, cereal, chips, etc) and incorporating high quality, animal-derived foods (eggs, meat, fish, offal). These changes on their own are a huge improvement over the standard diet in the U.S. and can result in rapid improvements in health.
It seems to me that most people aren't consuming a lot of oxalates in the first place. How many people do you know binging on spinach and dark chocolate? If you are having a large quantity of spinach in a greens smoothie every day, then unintentionally overdoing the oxalates is more likely, but if you consume a varied diet, things will tend to stay in balance.
It is certainly possible to over consume foods containing oxalates and it appears as if the limit is determined by one's individual metabolism and gut microbiome. Those with some type of gut dysbiosis seem to be more prone to experiencing negative effects and have a lower ability to break down oxalates in the gut. Given the widespread use of antibiotics and poor diets overall, this could potentially be a large percentage of the population. If you suddenly introduce large amounts of raw vegetables and leafy greens to your diet, you will likely have a hard time processing all of that unfamiliar (to your microflora) plant matter.
If I did have a recent history of kidney stones, I would keep high-oxalate foods to a minimum until I understood my capacity to digest them, and would only increase my consumption of these foods very gradually, assuming I had the goal of diversifying my diet. Sticking with a low-oxalate diet would be perfectly healthy as well, if a bit more limiting.
Do you have to eat foods that contain oxalates to be healthy? No, definitely not, but in general, I’m a proponent of maximum diversity in the diet. I see no reason to be fearful of spinach if you have a healthy microbiome and the spinach itself was grown in a healthy manner (i.e. not sprayed with poisons or grown with synthetic fertilizers.)
Thinking about the role of your microbiome and health
If consuming low to moderate amounts of oxalate-containing foods causes negative health consequences, this should alert you to the fact that there is likely an imbalance in your microbiome that needs your attention.
When you begin to think of the bacteria and other microorganisms in your gut as being an integral part of you (and not something separate), your thought process surrounding food and nutrition will become more intuitive.
Bacteria are able to synthesize key compounds inside your digestive tract like B-vitamins and vitamin K, along with neurotransmitters like serotonin and dopamine, but they need proper nutrition to fulfill their essential roles. When you keep your gut functioning optimally, good health follows!
References:
The Use of Antibiotics and Risk of Kidney Stones
Nutrient and antinutrient profiles of raw and fermented cocoa beans
Effect of Kimchi Fermentation on Oxalate Levels in Silver Beet (Beta vulgaris var. cicla)
Evaluation of Oxalate Concentration in the U.S. Spinach Germplasm Collection
The Effect of Maturity on the Oxalate Content of Spinach (Spinacia oleraceae L.)
