Understanding Oxalates and Their Impact
Oxalates are naturally occurring compounds found in many plants, including potatoes. In some individuals, particularly those prone to kidney stones, a diet high in oxalates can be problematic, as they can bind with calcium to form calcium oxalate crystals. While potatoes are a dietary staple, their oxalate content can vary significantly based on variety and preparation method. Knowing how to select and cook potatoes properly can make a big difference for those managing their oxalate intake.
How Oxalate Levels Vary by Potato Type
Not all potato varieties hold the same amount of oxalates. Scientific studies and nutritional data point to differences that can guide healthier choices.
- Russet Potatoes: The classic baking potato is often cited as having higher oxalate levels, particularly when the skin is consumed. The skin contains a significant concentration of oxalates, so peeling is essential for reduction. A medium baked Russet with skin can contain 97 mg of oxalates, while a peeled and boiled Russet has much less.
- Red-Skinned, White-Flesh “New” Potatoes: These varieties have been shown to have a lower oxalate content compared to Russets. A study found that peeled and boiled new potatoes tested at about half the oxalate level of a comparable Russet.
- Sweet Potatoes: Contrary to what many people assume, sweet potatoes, especially the deeply colored purple varieties, can be very high in oxalates. For instance, a half cup of mashed purple sweet potato can contain over 250 mg of oxalates. Orange-flesh sweet potatoes are also higher in oxalates than many believe.
- White Potatoes: Many diet guides list 'white potatoes' in the moderate-to-low oxalate range. However, this is a broad category, and preparation is still the key factor. When peeled and boiled, most standard white potato varieties are more suitable for a low-oxalate diet than their high-oxalate counterparts.
The Impact of Cooking Method on Oxalate Content
For most foods, preparation is just as important as the initial oxalate content. This is particularly true for potatoes, where certain cooking methods can significantly reduce oxalate levels.
- Boiling: This is the most effective method for reducing soluble oxalate content. The oxalates leach into the cooking water, and discarding that water removes a significant portion of the compound. A study found that boiling could reduce soluble oxalate content by 34%. This method is best for mashed potatoes, potato salads, or simply boiled potatoes.
- Baking: Baking, especially with the skin on, does not reduce oxalate levels effectively. The moisture loss during baking can even slightly concentrate the oxalates per gram of wet weight, leading to higher measured levels in the final product. This is why baked potatoes with skin have such high oxalate counts.
- Steaming: Steaming is less effective than boiling at reducing oxalates. While it is a healthy cooking method for many nutrients, it does not allow the soluble oxalates to be washed away with excess water.
- Frying (e.g., French fries, potato chips): Fried potatoes are considered very high in oxalates. This is likely due to retaining the skin (in many cases) and the lack of boiling to remove oxalates.
Low Oxalate Potato Varieties and Preparation
To enjoy potatoes while minimizing oxalate intake, a strategic approach is needed. The best option is to combine a low-oxalate variety with the correct preparation method.
Best Practices for Low-Oxalate Potato Consumption:
- Choose New Potatoes: Opt for red-skinned or white-flesh new potatoes, which have been shown to have naturally lower oxalate concentrations.
- Always Peel: Since a large concentration of oxalates resides in the skin, always peel your potatoes before cooking them.
- Boil and Discard Water: Always boil peeled potatoes thoroughly and throw away the cooking water. This leaches out a significant amount of the soluble oxalates.
- Mind Your Portions: Even with lower-oxalate varieties, moderation is key. A balanced diet prevents overconsumption of any single compound.
Potato Oxalate Content Comparison Table
| Potato Type | Preparation Method | Oxalate Level (Per 1/2 cup cooked) | Notes |
|---|---|---|---|
| Russet | Baked with skin | ~56 mg | Very high; skin contains high oxalate concentration |
| Russet | Peeled and boiled | ~20 mg | Moderate; peeling and boiling significantly reduces content |
| New Potatoes (Red/White) | Peeled and boiled | ~10-15 mg | Low; naturally lower in oxalates than Russets |
| Sweet Potato (Orange) | Boiled | ~28 mg (per cup) | Moderate; often higher than white potatoes when boiled |
| Sweet Potato (Purple) | Mashed | ~250+ mg (per 1/2 cup) | Very high; extremely high oxalate content |
| White Potato | Peeled and boiled | ~10-20 mg | Low-Moderate; varies by specific cultivar |
Pairing Potatoes with Calcium-Rich Foods
Consuming calcium-rich foods alongside high-oxalate foods can help minimize oxalate absorption in the body. Calcium binds with oxalates in the digestive tract, preventing them from being absorbed into the bloodstream. This is a common strategy for individuals on a low-oxalate diet. Pairing a peeled and boiled potato with a calcium-rich food, such as a serving of yogurt or a sprinkle of cheese, can be beneficial, though not a substitute for proper preparation. According to the Mayo Clinic Health System, consuming calcium in food can actually lower the risk of kidney stones.
Conclusion
While most potatoes contain some level of oxalates, knowing which varieties are best and how to prepare them is crucial for those on a low-oxalate diet. For the lowest oxalate potato, a good option is to choose a red-skinned, white-flesh new potato, peel it completely, and boil it thoroughly before eating. In contrast, avoid baked potatoes with the skin and be mindful of high-oxalate sweet potato varieties. By understanding these key distinctions, you can enjoy potatoes as part of a kidney stone-conscious diet without concern.
Optional Outbound Link
For more information on dietary choices for kidney stone prevention, consult resources from a trusted institution like the Mayo Clinic Health System: Preventing kidney stones before they form.
