What are oxalates?
Oxalates are naturally occurring molecules found in plants, animals, and humans. In plants, they serve various functions, including protecting against predators and assisting with calcium homeostasis. When humans consume foods containing oxalates, they travel through the digestive tract. Some of the oxalate can bind with minerals, primarily calcium, in the gut. For most healthy people, these bound compounds are excreted harmlessly in the stool.
The body also produces its own oxalates through metabolic processes, including the metabolism of vitamin C. These internally produced oxalates are normally filtered by the kidneys and excreted in the urine. It is when this delicate balance is disrupted that oxalates can become a concern.
How oxalates become harmful
The main reasons oxalates can be harmful revolve around their ability to bind with minerals and form crystals. This can lead to a number of health issues, particularly for those with a predisposition or certain underlying conditions.
Increased risk of kidney stones
High levels of oxalate in the urine, a condition known as hyperoxaluria, can cause oxalate to combine with calcium to form hard, sharp calcium oxalate crystals. These crystals can aggregate and form the most common type of kidney stones. Passing these stones can be extremely painful and may lead to complications like urinary tract infections. This risk is heightened when urine volume is low due to insufficient fluid intake.
Mineral absorption issues
Oxalates are considered an "anti-nutrient" because they can bind to essential minerals like calcium, magnesium, and iron in the digestive tract, making them less available for the body to absorb. While this is usually not a major problem for healthy individuals with a balanced diet, it can be a concern for those with existing mineral deficiencies or poor absorption. For example, despite spinach being rich in calcium, its high oxalate content significantly reduces the amount of calcium the body can utilize from it.
Systemic oxalosis
In severe cases, if kidney function is impaired, the body cannot effectively clear excess oxalate. This can cause oxalate to build up in the bloodstream and deposit as crystals in other tissues and organs, a condition called oxalosis. The deposits can cause damage to bones, blood vessels, the eyes, and the heart, leading to long-term health complications.
Gastrointestinal and inflammatory issues
Certain gut disorders, such as inflammatory bowel disease (IBD), can increase the body's absorption of oxalates. This is sometimes linked to a reduced population of Oxalobacter formigenes, a type of gut bacteria that helps break down oxalates. For some sensitive individuals, a high oxalate intake can also trigger inflammation, which may exacerbate conditions like joint pain, fibromyalgia, and leaky gut.
Managing oxalate intake
For most people, completely avoiding high-oxalate foods is unnecessary and can be detrimental, as many are highly nutritious. The key is moderation and dietary awareness, especially for those prone to kidney stones or with certain health conditions.
How to reduce your oxalate load
- Pair oxalates with calcium: Eating calcium-rich foods alongside high-oxalate foods allows the minerals to bind in the intestines, preventing a large amount of oxalate from being absorbed.
- Stay hydrated: Drinking plenty of water dilutes urine, helping to flush oxalates from the kidneys and preventing crystals from forming.
- Cook high-oxalate foods: Boiling and steaming can significantly reduce the oxalate content of vegetables, especially if you discard the cooking water.
- Limit vitamin C supplements: High doses of supplemental vitamin C can be metabolized into oxalate, increasing the body's load.
- Gradual reduction: If a low-oxalate diet is necessary, reduce intake gradually to avoid a rapid release of stored oxalates, a phenomenon known as oxalate dumping, which can cause unpleasant side effects.
High-oxalate foods vs. low-oxalate alternatives
Becoming aware of which foods are high in oxalates can help you make informed choices. Here is a general comparison:
| High-Oxalate Foods | Low-Oxalate Alternatives |
|---|---|
| Leafy Greens: Spinach, Swiss chard, Beet greens | Leafy Greens: Kale, Romaine lettuce, Cabbage, Bok choy |
| Vegetables: Rhubarb, Beets, Sweet potatoes | Vegetables: Broccoli, Cauliflower, Mushrooms, Onions |
| Nuts & Seeds: Almonds, Cashews, Peanuts, Tahini | Nuts & Seeds: Pumpkin seeds, Sunflower seeds |
| Legumes: Soybeans, some types of beans | Legumes: Lentils, some peas (in moderation) |
| Grains: Wheat bran, Brown rice, Quinoa | Grains: White rice, Oat bran |
| Beverages: Black tea, Cocoa, Chocolate milk | Beverages: Water, Coffee, Fruit juices low in oxalate |
Conclusion
Understanding what are oxalates and why are they harmful is key to managing your health. For the average person, consuming oxalate-rich foods as part of a balanced diet poses no significant risk. However, for individuals with a history of kidney stones, digestive disorders, or other predispositions, managing oxalate intake is a crucial part of preventing complications. By focusing on hydration, pairing high-oxalate foods with calcium, and adopting proper preparation methods, you can enjoy a nutritious diet while minimizing the potential harm from oxalates. Remember, a varied diet is a powerful tool against the concentration of any single compound. For more information, you can consult with your healthcare provider or a registered dietitian who can provide tailored dietary guidance. Learn more about the role of calcium and oxalates in kidney stones.
