What are oxalates?
Oxalates are a common, natural chemical component of many plant foods, including nuts, fruits, vegetables, grains, and is typically present as a salt of oxalic acid. We even make it via our own metabolism. It’s best to be mindful that excess vitamin C is converted to oxalate, so it’s wise to avoid supplementing with more than 500-1000mg vitamin C (ascorbic acid) per day. Luckily, you don’t need to worry about vitamin C naturally found in foods though, such as 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 that could affect oxalate absorption and 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 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 that is absorbed in our GI tract, appears to decrease when consumed with foods that contain minerals it can bind to.
Why might someone 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 to reduce exposure to certain foods that are high in oxalates which in turn will decrease irritation to the baldder, bladder pain, urgency, or frequency.
How do I know if a low oxalate diet is appropriate?
If you’ve been following the “traditional IC Diet” and you continue to have urgency, frequency, or pain, a low oxalate diet may be worth trying. If you suspect oxalates as a root cause of your 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 large variations in the reported oxalate content of various foods. The oxalate app is great for looking up the oxalate content of foods.
It’s best to stay under 100mg oxalates per day, but if you can stay under 50mg oxalates per day, 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 that have 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 seed, sunflower seeds, avocado, and meats. You could also consider supplementing 200mg calcium or magnesium with a meal but discuss it with your medical provider before starting. To learn more about the connection between oxalates and IC check our podcast! For help in identifying food and chemical intolerances or personalizing your diet please contact me here.