Oxalates are organic compounds found in a wide range of plant foods — from leafy greens and nuts to grains and chocolate. In small amounts, they pass through the body harmlessly. But when intake is chronically high or absorption is elevated, oxalates can bind to calcium and other minerals, form kidney stones, trigger inflammation, and potentially contribute to a range of symptoms that many people never connect to their diet.
The tricky part is that some of the highest-oxalate foods are the ones most aggressively marketed as health foods.
What Oxalates Are and How They Work
Oxalates (also called oxalic acid when in their acid form) are produced by plants as a natural defense against insects and grazing animals. When you eat a food containing oxalates, they bind to minerals — primarily calcium, but also magnesium, iron, and zinc — forming oxalate salts.
If this binding happens in the gut, the resulting calcium oxalate crystals are too large to be absorbed and exit through the stool. That's the best-case scenario. But when free oxalate molecules are absorbed through the intestinal wall into the bloodstream, they travel to the kidneys, where they can combine with calcium in the urine and form kidney stones. About 75-80% of kidney stones are calcium oxalate.
Beyond stones, emerging research suggests that oxalate crystals can deposit in other tissues — joints, bones, skin, eyes, and blood vessels — potentially contributing to pain, inflammation, and tissue damage. This area of study is still developing, but clinicians who treat high-oxalate patients report a consistent pattern of symptoms.
How Oxalates Accumulate
Your body handles oxalates through two pathways: gut excretion and kidney filtration. Problems arise when either pathway is overwhelmed.
Dietary overload. A single smoothie made with spinach, almond butter, and cocoa powder can deliver over 1,000mg of oxalates — roughly ten times the daily limit recommended for kidney stone prevention. Many health-conscious eaters consume high-oxalate foods at every meal without realizing it.
Gut bacteria loss. A bacterium called Oxalobacter formigenes specializes in breaking down oxalates in the gut. Antibiotic use can wipe out this population, and it may not fully recover. Without it, more dietary oxalate gets absorbed into the bloodstream.
Fat malabsorption. Conditions like Crohn's disease, celiac disease, or post-bariatric surgery can cause fat to bind calcium in the gut, leaving oxalates unbound and free to be absorbed. This is called enteric hyperoxaluria and is a well-documented clinical phenomenon.
Symptoms of High Oxalate Intake
Symptoms associated with chronic high oxalate consumption can be vague and wide-ranging, which is part of why the connection to diet is often missed:
- Kidney stones (sharp flank pain, blood in urine)
- Frequent or painful urination
- Joint pain and stiffness
- Skin rashes or hives
- Fatigue and brain fog
- Vulvodynia (chronic vulvar pain) — several studies have linked this to elevated urinary oxalate
- Sandy or gritty stools
Not everyone with a high-oxalate diet will experience these symptoms. Genetics, gut health, hydration, and calcium intake all influence individual tolerance.
Who Is at Risk
- Anyone who has had a calcium oxalate kidney stone. Recurrence rates are approximately 50% within 5-10 years.
- People with inflammatory bowel disease or other conditions causing fat malabsorption.
- Those who have taken repeated courses of antibiotics, particularly broad-spectrum types that reduce Oxalobacter populations.
- People eating large quantities of raw greens, nuts, seeds, and certain grains daily — especially in smoothies, juices, or salads where raw form maximizes oxalate exposure.
Getting Started With Lower Oxalate Eating
Reducing oxalates does not mean eliminating plants from your diet. It means choosing lower-oxalate options within each food group. Romaine lettuce, arugula, broccoli, cabbage, and cauliflower are all very low in oxalates while delivering strong nutritional profiles. Walnuts, pecans, and macadamia nuts are far lower than some other nuts. White rice, farro, and millet replace higher-oxalate grains without sacrificing versatility.
For a step-by-step framework, see our low oxalate diet guide, which covers daily targets, meal planning, and food-group swaps.
Navigate Oxalates When Dining Out
Restaurants don't label oxalate content, making it easy to unknowingly order a high-oxalate meal. DinePick analyzes menus in real time and highlights dishes that align with your dietary needs. Join the waitlist to try it first.