Oxalates, or oxalic acid, are naturally occurring compounds found in many plant-based foods, including fruits, vegetables, and nuts. For most healthy individuals, dietary oxalates are broken down by gut bacteria and excreted without issue. However, in susceptible individuals, such as those with a history of kidney stones or certain intestinal disorders, high oxalate intake can increase the risk of forming calcium oxalate crystals in the kidneys. Soaking has long been touted as a method to reduce these antinutrients, but its effectiveness specifically for oxalates in nuts is more nuanced than for other food types.
The Science Behind Soaking and Oxalates
Oxalates can be classified into soluble and insoluble forms. Soaking primarily affects the water-soluble oxalates through a process called leaching, where they dissolve and are washed away in the water. This mechanism is most effective when the soaking water is discarded. However, nuts have a dense structure, and the outer skin, particularly in nuts like almonds, can trap some compounds, making the leaching process less efficient for the whole nut.
While studies on legumes have shown significant reductions in soluble oxalates after soaking and boiling, the research on nuts presents a different picture. For instance, a study on almonds found that even after 24 hours of soaking, the reduction in phytate (another antinutrient) was minimal, suggesting a limited impact on other trapped compounds like oxalates. Furthermore, studies indicate that boiling is a more potent method for reducing oxalates in plant foods, as the higher temperature enhances the leaching process.
Soaking's Broader Benefits: Beyond Oxalates
While the impact of soaking on nuts' oxalate content may be modest, the practice offers other significant nutritional benefits. These are often the primary reason nutritionists recommend soaking nuts and seeds:
- Reduction of phytic acid: Soaking helps break down phytic acid, an antinutrient that can bind to essential minerals like zinc, magnesium, and iron, preventing their absorption. By neutralizing phytic acid, soaking increases the bioavailability of these minerals.
- Improved digestion: The presence of enzyme inhibitors in raw nuts can make them harder to digest for some people. Soaking deactivates these inhibitors, making the nuts gentler on the digestive system.
- Enhanced texture and flavor: Soaking softens the nuts, giving them a creamier texture. It also removes some of the tannins in the skin, which can result in a milder, less bitter taste.
Does Soaking Work for All Nuts? A Closer Look
When considering oxalate reduction, it is important to remember that not all nuts have the same oxalate levels. Almonds are particularly high in oxalates, making them a primary focus for those on a low-oxalate diet. Other nuts, like macadamias, walnuts, and pecans, are naturally lower in oxalates. For the latter, soaking for oxalate reduction is even less of a concern. Soaking whole nuts like almonds is less effective for reducing oxalates than other methods like chopping and boiling, which have shown more promising results in some studies, albeit with potential mineral loss.
Managing Oxalate Intake: Soaking vs. Other Methods
For individuals advised to limit their oxalate intake, relying solely on soaking may not be sufficient. A more comprehensive strategy includes:
- Boiling: Boiling high-oxalate foods and discarding the water is a highly effective way to reduce soluble oxalates. However, nuts are rarely prepared this way, and high heat can also degrade some nutrients.
- Pairing with Calcium-Rich Foods: Eating calcium-rich foods alongside high-oxalate foods is a very effective strategy. Calcium binds to oxalates in the digestive tract, preventing them from being absorbed into the bloodstream.
- Staying Hydrated: Drinking plenty of water helps flush excess oxalates from the kidneys, preventing the formation of calcium oxalate stones.
- Dietary Diversity: Rotating different nuts and greens is a simple way to avoid consuming large amounts of oxalates from a single source.
Nuts and Oxalates: A Comparative Table
| Nut Type | Relative Oxalate Level | Impact of Soaking on Oxalates | Notes |
|---|---|---|---|
| Almonds | High | Minimal effect on whole nuts; some leaching of soluble oxalates. | Soaking offers benefits for phytic acid and texture. |
| Cashews | High | Some reduction of soluble oxalates through leaching. | Best for texture and digestibility improvement. |
| Peanuts | High | Similar to other high-oxalate nuts; some soluble oxalate reduction. | Often cooked, which can reduce oxalates more effectively. |
| Walnuts | Low | Not a major concern; soaking improves digestibility. | Excellent low-oxalate alternative with high omega-3s. |
| Pecans | Low | Not a major concern; soaking improves digestibility. | Low-oxalate choice for those managing intake. |
| Macadamia Nuts | Very Low | Not necessary for oxalate reduction. | Safest nut for a low-oxalate diet. |
Conclusion
While soaking can lead to a minor reduction in soluble oxalates from nuts, it is not a foolproof method for complete removal, and its effectiveness is significantly less pronounced than with boiling. For most healthy people, the practice of soaking offers greater benefits by reducing phytic acid and enzyme inhibitors, thus improving digestion and mineral absorption. However, for individuals who are susceptible to kidney stones or have been medically advised to follow a low-oxalate diet, relying on soaking alone for substantial oxalate reduction is not recommended. Instead, focusing on a varied diet, proper hydration, and pairing high-oxalate foods with calcium sources is a more reliable strategy for managing oxalate intake. Consulting a healthcare professional or a dietitian is always the best course of action for personal dietary modifications.
Read more from the National Institutes of Health about diet and nutrition for kidney stones
