Oxalates, or oxalic acid, are naturally occurring compounds found in many plants, including some of the most nutrient-dense vegetables, fruits, nuts, and legumes. While harmless for most people, for individuals with a history of kidney stones or certain gastrointestinal conditions, high oxalate intake can pose a health risk. When consumed, oxalates can bind with minerals like calcium and iron in the gut, reducing their bioavailability and potentially forming calcium oxalate crystals in the kidneys, which account for about 80% of kidney stones. Understanding what destroys oxalates is therefore crucial for managing dietary intake and mitigating these risks.
Cooking Techniques that Reduce Oxalates
Some of the most practical methods for reducing oxalate content are simple cooking techniques that utilize water to leach out the soluble oxalates. As plants contain both soluble and insoluble oxalates, these methods primarily target the more easily absorbable soluble form.
The effectiveness of water-based cooking
- Boiling: This is the most effective method for reducing soluble oxalate levels. Boiling vegetables in water for several minutes allows the soluble oxalates to leach out into the liquid. Studies on spinach, for instance, have shown a reduction of over 60% after boiling. It is crucial to discard the boiling water and not use it for cooking or consumption, as it contains the leached oxalates.
- Blanching: A quick dip in boiling water followed by an ice bath, blanching also leverages the leaching effect of water to remove a significant portion of oxalates, though often less effectively than a full boil.
- Steaming: While steaming is a healthier cooking method that preserves more vitamins, it is less effective at removing oxalates compared to boiling because there is no direct liquid for the compounds to leach into.
- Soaking: For foods like legumes, soaking them for several hours, or even overnight, can help reduce the oxalate content. Always discard the soaking water before proceeding with cooking.
Binding Oxalates Before Absorption
Instead of physically destroying oxalates, another highly effective strategy is to bind them in the digestive tract so they are not absorbed into the bloodstream. This prevents them from reaching the kidneys where they can form crystals.
The power of calcium
Consuming calcium-rich foods alongside high-oxalate foods is an established method to mitigate their impact. When oxalate and calcium are present together in the gut, they bind to form insoluble calcium oxalate, which is then excreted in the stool.
- Pairing high-oxalate foods like spinach with dairy products such as milk, yogurt, or cheese can effectively reduce oxalate absorption.
- Low-oxalate calcium sources like bok choy and broccoli are also excellent choices.
- It is generally recommended to get calcium from food sources rather than supplements, as calcium supplements may increase the risk of kidney stone formation.
Microbial Action: Fermentation and Gut Health
The body's own microbiome plays a significant role in breaking down oxalates. Certain bacteria in the gut, notably Oxalobacter formigenes, use oxalate as an energy source, which substantially reduces the amount of oxalate absorbed by the body.
Leveraging beneficial microorganisms
- Fermentation: This traditional food processing method can reduce the oxalate content in foods. Lactic acid fermentation, for example, has been shown to reduce antinutrients like oxalates in certain vegetables and legumes. Fermented foods may also promote a healthy gut microbiome, which in turn can aid in oxalate degradation.
- Gut Health: Maintaining a healthy gut with beneficial bacteria is essential for endogenous oxalate breakdown. Factors like antibiotic use or inflammatory bowel diseases can disrupt the balance of gut bacteria and increase oxalate absorption.
Comparison of High-Oxalate Foods and Low-Oxalate Alternatives
| High-Oxalate Food (≥50 mg/100g) | Low-Oxalate Alternative (<10 mg/100g) | Primary Oxalate Reduction Strategy |
|---|---|---|
| Spinach | Romaine Lettuce | Boil spinach, discard water; or swap for low-oxalate greens |
| Rhubarb | Apples or Pears | Boil rhubarb with milk (calcium) or choose low-oxalate fruits |
| Almonds | Pistachios or Sunflower Seeds | Consume almonds with calcium-rich dairy; or opt for low-oxalate seeds |
| Beets | Mushrooms or Radishes | Boil beets, discard water; or substitute with low-oxalate vegetables |
| Sweet Potatoes | White Potatoes (without skin) or Cauliflower | Boil sweet potatoes, discard water; or choose low-oxalate starch |
Managing Oxalates in Your Diet
For most people, a balanced diet including a variety of fruits and vegetables is the best approach. However, for those with specific health concerns, actively managing oxalate intake is recommended. A low-oxalate diet might involve limiting high-oxalate foods to under 100 mg per day, or even 50 mg in very high-risk cases. Strategic food preparation and pairing can make this manageable. It is always best to consult a healthcare professional or a registered dietitian before making significant dietary changes. More research continues to evolve in this field, offering new insights into nutrient interactions and food processing techniques to improve nutritional outcomes.
Conclusion
Addressing the question of what destroys oxalates involves a multifaceted approach, combining preparation methods, strategic food pairing, and supporting gut health. Boiling and soaking foods effectively leach soluble oxalates away, while consuming adequate calcium binds them in the gut, reducing absorption. Fermentation and a healthy microbiome also contribute to breaking down these compounds. By understanding these mechanisms, individuals with oxalate sensitivity can manage their intake without sacrificing nutrient-rich foods, allowing for a more balanced and safer diet.
