Understanding Oxalates and the Science of Soaking
Oxalates, or oxalic acid, are naturally occurring compounds found in many plant-based foods. When consumed, they can bind with minerals like calcium, potentially inhibiting nutrient absorption and contributing to the formation of kidney stones in susceptible individuals. Soaking is a powerful yet simple method for reducing oxalate levels, particularly the soluble form, by leveraging their water-solubility. As foods sit in water, the soluble oxalates leach out into the liquid, which is then discarded. For maximum efficacy, soaking is often combined with other heat-based cooking methods like boiling or blanching.
General Principles for Effective Soaking
For most food groups, the fundamental process of soaking remains consistent, though times and techniques vary. Key steps include using filtered water and a non-reactive container. Adding an acidic medium is sometimes suggested for grains to break down antinutrients, though not specifically for oxalate reduction. The most critical steps are discarding the soaking water, which contains the leached oxalates, and thoroughly rinsing the food afterward.
Step-by-Step Soaking Guide for Specific Foods
Different food types require specific soaking treatments.
Soaking Nuts and Seeds
High-oxalate nuts include almonds, cashews, and peanuts. Place raw nuts or seeds (excluding chia and flax) in a glass bowl, cover with filtered water, and add a little sea salt. Soak for 8-12 hours, drain, and rinse thoroughly before dehydrating or roasting.
Soaking Legumes
Sort and rinse dried beans or lentils. Cover with hot water and soak for at least 12-24 hours, changing the water at least once. Drain and rinse before cooking; cooking after soaking is important for reducing remaining antinutrients. Soaking in distilled water for 4 hours followed by cooking significantly reduced oxalates in a study.
Soaking High-Oxalate Vegetables
Chop leafy greens like spinach to increase surface area. Submerge in hot water (around 80°C). Soaking spinach for 60 minutes at 80°C was effective in a study. A 30-60 minute soak in warm water can be helpful for home cooks. Drain, rinse, and note that boiling or blanching is even more effective.
Soaking Whole Grains
Cover unmilled whole grains like brown rice with warm, filtered water. Soak for 12-24 hours. Drain the water completely and rinse thoroughly before cooking in fresh water.
Soaking vs. Boiling for Oxalate Reduction
| Feature | Soaking (Pre-Cooking) | Boiling (Post-Soaking or Direct) |
|---|---|---|
| Efficacy for Oxalates | Moderate, especially for soluble oxalates. | High, especially when combined with soaking and discarding the water. |
| Nutrient Retention | Better retention of heat-sensitive nutrients. | Higher loss of water-soluble vitamins, even after discarding the water. |
| Time Commitment | Requires pre-planning and can take up to 24 hours. | Faster; can be done in minutes for vegetables. |
| Best for | Foods eaten raw (e.g., nuts, some sprouted seeds) or as a pre-treatment. | Leafy greens and root vegetables where maximum reduction is needed. |
| Process | Submerging food in water, draining, and rinsing. | Cooking food in a pot of water, then draining. |
Combining Methods for Maximum Reduction
For the highest oxalate reduction, especially in high-oxalate greens, a multi-step process is most effective. Start with a 30-60 minute soak in warm water, discard the water, and then blanch or boil in fresh water. Boiling can remove up to 87% of soluble oxalates in vegetables. Drain and rinse again after boiling. Combining soaking with steaming can also be effective, although steaming removes fewer oxalates than boiling.
Conclusion
Soaking is a valuable and simple technique to lower the oxalate content of many plant foods, making them more suitable for a low-oxalate diet. It is most effective for water-soluble oxalates and serves as a good preparation step before further cooking. By using the appropriate methods for different foods like nuts, grains, legumes, and vegetables, you can confidently prepare meals to meet your nutritional needs. Always discard the soaking water and consider a final heat-based cooking step for the greatest reduction. Consult a healthcare professional for dietary changes, especially if managing conditions like kidney stones. You can find more information about reducing antinutrients from sources like Healthline.
What are oxalates and why should you reduce them?
Oxalates are natural compounds in plants that can hinder mineral absorption and may contribute to kidney stone formation in sensitive individuals. Reducing them can improve mineral absorption and lower kidney stone risk.
Does adding salt help reduce oxalates during soaking?
Adding salt is typically used for soaking nuts to reduce other antinutrients like phytic acid, not specifically oxalates. The reduction of oxalates relies on their water-solubility and discarding the soaking liquid.
How long should you soak legumes to reduce oxalates?
Dried legumes should be soaked for at least 12-24 hours with at least one water change to effectively reduce oxalates. Following soaking with cooking, such as boiling, is recommended for maximum reduction.
Is it possible to remove all oxalates by soaking?
No, soaking primarily removes soluble oxalates by leaching and cannot eliminate them completely. A significant amount of insoluble oxalates often remains in food even after soaking and cooking.
Do you need to soak all high-oxalate foods?
Soaking is particularly useful for raw or less-processed high-oxalate foods like nuts, seeds, and legumes. For leafy greens, blanching or boiling is often more effective than soaking alone due to their higher initial oxalate content.
Can I use a low-oxalate diet without soaking?
A low-oxalate diet can be effective without soaking by focusing on low-oxalate foods and limiting portions of high-oxalate items. However, soaking provides an extra tool to include moderate amounts of high-oxalate foods with less impact.
Should I soak vegetables in hot or cold water?
Using warm or hot water (around 80°C) is more effective for leaching soluble oxalates from vegetables like spinach compared to cold water. Higher temperatures enhance the leaching process.
