Navigating Oxalates: How to Improve Calcium Absorption for Stronger Bones

What are oxalates and what do we need to know about them? Oxalates (also called oxalic acids) are naturally occurring compounds in several plant-based foods, sometimes called "anti-nutrients" — substances that impede absorption of certain nutrients. Oxalates specifically impact absorption of calcium, magnesium, and iron, reducing their bioavailability and potentially affecting bone health.

Are oxalates harmful? When calcium-rich foods are eaten alongside oxalate-rich foods, calcium binds to oxalates in the digestive tract, decreasing (but not eliminating) calcium bioavailability, potentially leading to deficiency over time. Oxalates are generally harmless in moderate amounts and typically excreted in urine, but if oxalate-rich foods dominate the diet without adequate mineral intake or proper preparation, there's a possible risk of mineral deficiencies affecting bone health.

What foods are high in oxalates? almonds, avocados, beets and beet greens, cashews, chard, cocoa products, dark chocolate, dates, grains (wheat flour, whole grain products), grapefruit, legumes (navy, red kidney, fava beans), okra, parsley, peanuts, raspberries, rhubarb, sesame seeds, spinach, tofu, yams. This is just a sampling — the answer to whether these foods should be eliminated is a resounding "No!"

Dietary strategies: reducing the impact of oxalates.

• Food preparation: boiling high-oxalate vegetables significantly reduces oxalate content (oxalates are water-soluble and leach into cooking water — discard the water to maximize reduction); steaming or baking reduces content to a lesser extent.
• Separate calcium-rich and high-oxalate foods: eat calcium-rich foods (cheese, yogurt, fortified plant milks) at different times than high-oxalate foods.
• Drink plenty of water: dilutes oxalates and promotes healthy kidney function.
• Moderate consumption of high-oxalate foods (smaller portions, less frequently).
• Substitute low-oxalate greens: arugula, romaine lettuce, iceberg lettuce, kale, cabbage, mustard and turnip greens, bok choy, watercress, butter lettuce, endive.

Be aware that some people are at greater risk:

• People prone to kidney stones (particularly calcium oxalate stones) — high oxalate intake can increase risk, since oxalate-produced salts can crystallize in urine and trigger stone formation.
• Malabsorption disorders (Crohn's, Celiac disease) — may exacerbate oxalate-related mineral absorption problems.
• Existing kidney disease — reduced kidney function hampers oxalate excretion.
• Hyperoxaluria — a rare condition of excessive urinary oxalate, hereditary or secondary to other health issues.

If you have any of these conditions, consult your healthcare provider for personalized dietary guidance.

The takeaway. While many oxalate-containing foods are part of a healthy diet for most people, excessive consumption without consideration can impact mineral absorption and bone health. Balancing oxalate-rich foods with calcium intake and overall nutritional health are key strategies for supporting strong bones.

Oxalate technically refers to the acid after it has bound to minerals like calcium, while oxalic acid is the free, organic acid form. For a comprehensive list of oxalic acid content in foods, see the University of California at Irvine's Oxalate Content of Foods PDF.

References

1. Gaur A, et al. Food Oxalates: Occurrence in the Food System and Advances in Technologies for Reduction, Detection, and Quantification. Comprehensive Reviews in Food Science and Food Safety. 2025;24(4):e70212.