What Exactly is Purslane?
Purslane (Portulaca oleracea) is a common, annual succulent that grows in many parts of the world. It is known for its slightly salty or sour taste, similar to spinach or watercress, and is used in cuisines across the globe, especially in Mediterranean and Asian regions. Beyond its culinary use, purslane is celebrated for its impressive nutritional profile, packed with omega-3 fatty acids, vitamins (A, C, and E), and minerals. However, like other leafy greens such as spinach and sorrel, it is also notable for its high concentration of oxalates.
How Much Oxalate is in Purslane?
The amount of oxalate in purslane is not a single, fixed number; it can vary substantially. Research shows that oxalate content is influenced by several factors, including the part of the plant, its maturity, and environmental conditions like light exposure. A study published in the Journal of Food, Agriculture & Environment revealed total oxalate content in raw leaves at 23.45 g/kg fresh weight (FW), equivalent to 2,345 mg/100g FW. Other studies have reported levels in the range of 671–869 mg/100g fresh weight. For context, a standard serving of spinach is often cited as containing 600-700 mg per 100g.
Crucially, oxalates exist in two forms: soluble and insoluble. Soluble oxalates are more readily absorbed by the body, whereas insoluble oxalates bind to minerals like calcium and pass through the body largely unabsorbed. Purslane leaves contain a higher proportion of insoluble oxalates compared to stems and buds, which have a greater percentage of soluble oxalates.
The Impact of Cooking and Preparation
Fortunately, processing and preparation techniques can reduce the amount of absorbable oxalate in purslane. The key is to reduce the soluble oxalate content, as this is the form that poses the most risk. Boiling is one of the most effective methods, as soluble oxalates leach into the cooking water, which is then discarded. Research has demonstrated that boiling can decrease the soluble oxalate content in purslane leaves, with one study showing a 33.5% loss after a 5-minute boil.
Another highly effective method involves consuming purslane with a calcium-rich food. Calcium readily binds with soluble oxalates, forming insoluble calcium oxalate salts that are not absorbed by the digestive tract. Traditional Mediterranean dishes often pair purslane with yogurt, a practice that has been scientifically shown to significantly reduce the bioavailability of soluble oxalates.
Purslane Oxalate Levels: Raw vs. Cooked Comparison
| Preparation Method | Effect on Soluble Oxalate | Effect on Total Oxalate | Notes |
|---|---|---|---|
| Raw | Highest level | Highest level | Offers the full nutritional benefit but also the highest oxalate exposure. |
| Boiled (5 min) | Reduced by approximately one-third | Reduced, but less than soluble portion | Some soluble oxalates are lost to the cooking water. |
| Boiled (25 min) | Significantly decreased | Significantly decreased | Longer boiling maximizes oxalate removal but may also reduce other nutrients. |
| With Calcium Source (e.g., Yogurt) | Significantly reduced absorption | Bioavailability reduced, total content unchanged | Calcium binds to soluble oxalates in the gut, preventing absorption. |
| Pickled | Reduced | Reduced by 16% | Leaches soluble oxalates into the pickling liquid. |
Who Should Be Cautious About Consuming Purslane?
While purslane is a healthy food for most people when consumed in moderation, certain individuals should exercise caution or avoid it entirely due to its high oxalate content.
- Individuals prone to kidney stones: Oxalates are a major component of kidney stones. For those with a history of calcium oxalate stones, a high-oxalate diet can increase the risk of recurrence.
- People with kidney disease: Chronic kidney disease and other kidney problems can affect the body's ability to excrete oxalates, making high-oxalate foods a potential concern.
- Individuals on sodium-restricted diets: Due to its succulent nature, purslane can be naturally high in sodium, which is important for those managing blood pressure or other conditions requiring a low-sodium intake.
- Pregnant and breastfeeding women: Limited information is available regarding purslane consumption during pregnancy, and some sources advise caution.
Safe Consumption Tips
For those who enjoy purslane, a few simple tips can help maximize its nutritional benefits while minimizing oxalate intake.
- Practice Moderation: Incorporate purslane into meals as part of a varied diet rather than consuming excessive quantities regularly.
- Blanch and Drain: For cooking, a quick boil (blanching) for 5 minutes, followed by draining and rinsing, is effective at reducing soluble oxalate levels.
- Pair with Calcium-Rich Foods: Combining purslane with ingredients like yogurt, cheese, or milk products is a traditional and scientifically supported method to reduce oxalate absorption.
- Choose Cultivated Varieties: Some cultivated purslane varieties have been found to have lower oxalic acid content than wild types.
- Use Young Plants and Leaves: Younger leaves may contain less oxalate than larger, more mature leaves.
- Be Aware of Source: Never consume wild purslane if there is a possibility it has been treated with herbicides, as this can make it toxic.
For more safety information on herbal plants and supplements, consult authoritative sources like The University of Texas at El Paso's herbal safety resource: UTEP Herbal Safety: Purslane.
Conclusion
Ultimately, the question of "how much oxalate is in purslane" has a complex answer, revealing a vegetable that is both a nutritional powerhouse and a significant source of oxalates. While its rich supply of omega-3s and antioxidants is beneficial, the high oxalate content is a valid concern for individuals prone to kidney stones or with kidney health issues. By understanding the factors that influence oxalate levels and utilizing simple preparation methods like boiling or pairing with calcium-rich foods, most people can continue to enjoy the health benefits of this flavorful green as part of a balanced diet. As with any dietary change, informed moderation is key to a healthy approach.
