What are oxalates?
Oxalates are a common, naturally occurring chemical component found in many plant-based foods, including nuts, fruits, vegetables, and grains. Typically existing as a salt of oxalic acid, they're even produced by our own metabolism. It's important to note that excess vitamin C can be converted into oxalates, making it wise to avoid supplementing with more than 500-1000mg of vitamin C (ascorbic acid) daily. However, there's no need to worry about the natural vitamin C found in foods like bell peppers, broccoli, or Brussels sprouts.
What does our gut have to do with oxalates?
Oxalate degradation by oxalate-degrading bacteria within the GI tract is another key factor affecting oxalate absorption and the degree of oxaluria. These bacteria include Oxalobacter formigenes, numerous species of Lactobacillus, Enterococcus, and Bifidobacteria. The good bacteria in the gut help get rid of oxalate, and when the levels of these bacteria are low, due to taking antibiotics, for example, higher amounts of oxalate can be absorbed in the body. Studies that have assessed the efficacy of oral ingestion of probiotics that provide bacteria with oxalate-degrading capacity are promising, but this requires future studies. Some people may be hyper absorbers of oxalate due to having a damaged gut lining or leaky gut (gut health is key in addressing interstitial cystitis (IC) and supporting immune function). An inflamed or damaged gut lining can occur for many reasons, including antibiotic use or eating conventional foods that contain higher levels of pesticides or herbicides like glyphosate.
Oxalic acid is a highly reactive compound that is attracted to positively charged minerals such as calcium, magnesium, and potassium. Calcium oxalate and magnesium oxalate are insoluble or unable to be absorbed, while potassium oxalate is soluble or able to be absorbed. Therefore, the oxalate bioavailability, or the portion of oxalate absorbed in our GI tract, appears to decrease when consumed with foods containing minerals it can bind to.
Why might someone with interstitial cystitis need to follow a low-oxalate diet?
When oxalates enter the bloodstream and filter through the kidney to enter the bladder, they can form crystals. These oxalate crystals are thought to resemble broken glass structures, which irritate the bladder lining and potentially attach to glycoproteins and form bladder calculi. Following a low oxalate diet can help reduce exposure to certain foods that are high in oxalates, decreasing irritation to the bladder, bladder pain, urgency, or frequency.
How do I know if a low oxalate diet is appropriate?
A low oxalate diet may be worth trying if you’ve been following the “traditional IC Diet” and continue to have urgency, frequency, or pain. If you suspect oxalates as a root cause of your interstitial cystitis (IC), you may want to consider getting a 24-hour urine test for oxalates. If your level is greater than 31 mg/24 hours for women or greater than 44 mg/24 hours for men, then you would benefit from following a low oxalate diet. There is also a gene mutation involved, called SLC26A1, which can predispose someone to higher urinary oxalate levels. Genetic testing and supplementation may help those that are genetically predisposed to oxalates by supporting specific pathways in the body. Please note that a low oxalate diet may not be appropriate for someone to trial without the support of a dietitian if they have a history of an eating disorder or are currently underweight, as the low oxalate diet can be overly restrictive.
What foods are high in oxalates?
There is no gold standard oxalate reference database, and there are significant variations in the reported oxalate content of various foods. The oxalate app is excellent for looking up the oxalate content of foods. It’s best to stay under 100mg oxalates daily, but if you can stay under 50mg oxalates daily, that is ideal! The foods most commonly responsible for raising urine oxalate levels are rhubarb, dark leafy greens (spinach, chard, arugula), beets, wheat bran, nuts, soy, chocolate, black/green tea, and strawberries.
Low oxalate foods to focus on are vegetables: red bell pepper, bok choy, cabbage, cauliflower, cucumber, mushrooms, peas, radishes, squash, and zucchini. fruits: apples, blueberries, pears starches: white/wild rice, ½ cup cooked – blackeyed peas, chickpeas, split peas, lentils proteins: beef, chicken, pork, eggs, fish, shellfish beverages: coconut or flaxseed milk, herbal tea.
How else can I decrease my absorption of oxalates?
Recent data indicates that boosting your intake of calcium-rich foods when you eat foods that are high in oxalate may be a better approach than simply trying to eliminate oxalate from the diet. To help prevent the absorption of oxalates, it’s good to pair calcium or magnesium-rich foods with foods that contain moderate amounts of oxalates. Foods with low to moderate amounts of oxalates but adequate amounts of calcium include bok choy, broccoli, herring (canned with bones), oysters, fortified coconut, or flax milk. Magnesium-rich foods include pumpkin seeds, sunflower seeds, avocados, and meats. You could also consider supplementing 200mg of calcium or magnesium with a meal but discuss it with your medical provider before starting.
While oxalates are indeed present in a variety of plant-based foods and are a natural part of our diets, it's worth considering their potential impact on health, especially for individuals with conditions like interstitial cystitis. By understanding their role and being mindful of sources high in oxalates, we can make informed choices that support our well-being without compromising nutritional variety.