The Truth About Purslane and Oxalates
Purslane, known botanically as Portulaca oleracea, is a succulent leafy green often found growing as a weed in gardens and fields. Despite its humble origins, it is a nutritional powerhouse, celebrated for its high content of omega-3 fatty acids, vitamins, and antioxidants. However, its high oxalate content is a well-documented and important consideration for consumers. Oxalates are naturally occurring compounds found in many plants, and when consumed in large quantities, they can pose health risks for certain individuals. Purslane is consistently categorized as a high-oxalate food, alongside other greens like spinach and Swiss chard.
Soluble vs. Insoluble Oxalates in Plants
To fully understand the health implications, it's essential to differentiate between the two types of oxalates found in plants: soluble and insoluble. Soluble oxalates are free and can bind with minerals like calcium in the body, potentially forming calcium oxalate crystals. These crystals are the most common component of kidney stones and can also affect mineral absorption. Insoluble oxalates are bound to calcium within the plant itself and are generally not absorbed by the body. The proportion of these two types varies by plant part and growing conditions. Research indicates that different parts of the purslane plant contain varying ratios of soluble and insoluble oxalates, with leaves often having the highest overall concentration. The high level of soluble oxalates in raw purslane is the primary concern for those on a low-oxalate diet.
How Purslane Compares to Other High-Oxalate Foods
It is helpful to see how purslane's oxalate levels stack up against other common high-oxalate foods. Here is a comparison based on fresh weight data from various studies:
| Food Item | Total Oxalate (mg/100g Fresh Weight) |
|---|---|
| Raw Purslane Leaves | 235 - 1294 (depending on cultivar/conditions) |
| Raw Spinach | ~656 |
| Cooked Spinach | ~755 (concentration increases due to water loss) |
| Raw Swiss Chard | ~613 |
| Rhubarb | ~541 (cooked) |
As the table illustrates, purslane's oxalate content can be quite high, sometimes exceeding that of spinach, especially when considering the range of values reported in different studies. This underscores the need for cautious consumption, particularly for susceptible individuals. For further research, explore oxalate content in various vegetables.
Mitigating Oxalates with Proper Preparation
Fortunately, the soluble oxalates, which are of the greatest health concern, can be effectively reduced through simple culinary techniques.
- Boiling: This is the most effective method for reducing soluble oxalate levels. Research shows that boiling purslane for as little as 5 minutes and discarding the cooking water can lead to a significant loss of soluble oxalates. Longer boiling times (up to 25 minutes) can result in even greater reductions, but also risks losing more nutrients.
- Blanching and Draining: Similar to boiling, blanching involves briefly submerging the purslane in boiling water, then transferring it to an ice bath. The greens are then drained and the blanching water is discarded, which removes a large portion of the soluble oxalates.
- Combining with Calcium: Eating purslane with a calcium-rich food, such as yogurt or cheese, can significantly reduce the bioavailability of soluble oxalates. The calcium binds with the soluble oxalate in the digestive tract, creating insoluble calcium oxalate that is not absorbed and is instead excreted. This is a traditional practice in some cultures, such as the Turkish dish “Yogurtlu Semizotu” (purslane with garlic yogurt).
- Pickling: Studies have also found that pickling purslane can cause a reduction in soluble oxalates as they leach into the vinegar.
Health Considerations and Risks
For most people who consume purslane as part of a varied diet and in moderate amounts, the oxalate content is not a major concern. However, for individuals with a history of calcium oxalate kidney stones or other kidney problems, excessive intake could be problematic. Case reports exist documenting acute kidney injury (oxalate nephropathy) in patients who consumed unusually high quantities of purslane. This highlights the importance of moderation and proper preparation for those at risk.
Conclusion
So, is purslane high in oxalates? The answer is a clear yes. Purslane is a nutrient-dense vegetable that is naturally high in oxalates, particularly the soluble type that can contribute to kidney stone formation. However, this does not mean it needs to be avoided entirely. By employing simple cooking techniques like boiling and discarding the water, or by pairing it with calcium-rich foods, you can significantly reduce the soluble oxalate content. For the general population, consuming purslane in moderation as part of a balanced diet poses little risk. Those with a history of kidney stones or kidney disease should consult a healthcare provider for personalized dietary advice before adding purslane to their meals and should always prioritize mitigating the oxalate content through proper preparation.
