Understanding Oxalates: What Are They and Why Do They Matter?
Oxalates, or oxalic acid, are naturally occurring compounds found in many plants, including fruits, vegetables, nuts, seeds, and grains. For most people, consuming oxalate-rich foods poses no problem, as the body can process and excrete excess oxalates. However, for a smaller subset of the population, particularly those with a history of calcium oxalate kidney stones or certain digestive conditions, a high intake of oxalates can be problematic. When oxalates accumulate in the body, they can bind with calcium to form crystals, potentially contributing to kidney stone formation. The key takeaway is that not all foods containing oxalates are equal; some, like spinach and rhubarb, contain very high levels, while others, like oats, contain much less.
The Breakdown of Oxalate Content in Oats
Determining if oat is high in oxalates is more complex than it sounds, as the answer depends on the type of oat and its preparation.
Steel-Cut vs. Rolled vs. Instant Oats
- Steel-Cut Oats: These are the least-processed form of oats, made by chopping the groat into pieces. Because they undergo less processing with water, they likely have the highest oxalate content among the oat varieties, though still considered low to moderate compared to truly high-oxalate foods like spinach.
- Rolled Oats: These are steamed and rolled flat, a process that slightly reduces their oxalate content compared to steel-cut oats.
- Instant Oats: This is the most processed variety, parboiled to speed up cooking time. The parboiling process, which involves cooking the oats in water and then dehydrating them, is highly effective at leaching out water-soluble oxalates. Some studies have even found virtually no oxalates in instant oatmeal.
How Cooking Methods Reduce Oxalates
For those concerned about oxalate intake, specific cooking techniques can further lower the levels in oats.
- Soaking: Soaking oats overnight can help release some of the water-soluble oxalates. Draining the water and rinsing the oats before cooking is recommended to remove these compounds.
- Cooking and Draining: Similar to soaking, cooking oats in a generous amount of water and then draining the excess can reduce the oxalate load. This is more practical for steel-cut or rolled oats than instant oats, which absorb all the cooking water.
Oats Compared to Other Grains
When placed side-by-side with other grains, oats are generally on the lower end of the oxalate spectrum.
Oat and Oxalate Levels
- Oat bran has been shown to contain low levels of both total and soluble oxalates when compared to wheat and rice bran.
- Studies have indicated that whole oat flour can contain 0 oxalates, whereas white flour can have slightly higher levels.
Comparison Table: Oxalate Content in Common Grains (per 100g dry weight)
| Grain Type | Approximate Oxalate Content (mg/100g) | Typical Serving Preparation | Notes |
|---|---|---|---|
| Oats (raw) | 16 mg | Cooked with water/milk | Lower end of the moderate range |
| Oatmeal (cooked) | 9.3 mg | Cooked oats, ready to eat | Cooking reduces content |
| Instant Oats | 0 mg | Cooked and dehydrated | Parboiling removes nearly all oxalates |
| Rice Bran | 139.5 mg (total) | Added to foods | Significantly higher than oat bran |
| Wheat Bran | 220.8 mg (total) | Added to foods | Very high in oxalates |
The Role of Calcium and Other Considerations
Interestingly, the calcium-to-oxalate ratio in oats is favorable, meaning the amount of calcium present is higher than the oxalate content. This is significant because calcium binds to oxalate in the gut, forming an insoluble compound that the body cannot absorb. This binding process prevents the oxalate from entering the bloodstream and traveling to the kidneys. Therefore, consuming oats with a source of calcium, such as milk or yogurt, can help mitigate the effects of the oxalates that remain.
For most healthy individuals, the oxalate content in oats is not a concern. The benefits of including oats in a diet—such as their high fiber content, which promotes digestive health and can help lower cholesterol—far outweigh the risks associated with their modest oxalate levels. Concerns should only arise for individuals with specific medical conditions like hyperoxaluria or a history of calcium oxalate kidney stones, and even then, processed or properly prepared oats are often considered safe in moderation.
Conclusion: The Final Verdict
In summary, the notion that oat is high in oxalates is a common misconception, particularly when compared to foods that are truly rich in the compound like spinach and rhubarb. The oxalate content in oats is low to moderate and can be significantly reduced through standard cooking processes, especially the parboiling used for instant oats. The preparation method, whether soaking or cooking, further minimizes the oxalate load. For the average person, consuming oats is a healthy choice, and the inherent calcium in oats can even help manage the small amount of oxalate present. For those on a restricted low-oxalate diet, processed oat varieties and strategic cooking can ensure they can still enjoy the nutritional benefits of this versatile grain.
Can I eat oatmeal on a low-oxalate diet?
Yes, in many cases, oatmeal is considered a low-oxalate food and can be part of a managed low-oxalate diet. The preparation method and portion size should be considered, and consulting with a dietitian is recommended.
What is the oxalate content of instant oatmeal?
Instant oatmeal has a very low, and sometimes zero, oxalate content because the parboiling process used during its production leaches out the water-soluble oxalates.
Does cooking oats reduce oxalates?
Yes, soaking and cooking oats, especially if you discard the water afterward, are effective ways to reduce their oxalate content.
Are steel-cut oats higher in oxalates than rolled oats?
Steel-cut oats are generally believed to have a slightly higher oxalate content than rolled oats because they are less processed with water during manufacturing.
How can I reduce the oxalate content of my homemade oatmeal?
You can reduce the oxalate content by soaking your oats overnight, then draining and rinsing them before cooking. Cooking them in a pot with excess water that is then drained can also be effective.
Do all types of oats have the same oxalate content?
No, the oxalate content varies by the type of oat and its processing. Instant oats have the lowest levels, while less-processed varieties like steel-cut oats have slightly more.
Are oats a concern for kidney stones?
For most people, oats are not a concern for kidney stones. The oxalate content is moderate at most, and the calcium-to-oxalate ratio is favorable. Individuals with a history of kidney stones should consult a healthcare provider.
