Does Sourdough Break Down Oxalates?

November 2, 2025 •

4 min read

Studies have shown that fermentation can significantly reduce oxalate levels in certain foods, making them potentially more tolerable for some individuals. This leads many to ask: does sourdough break down oxalates, and can it improve the nutritional profile of bread?

Quick Summary

Sourdough fermentation can reduce oxalate content in flour and other plant-based foods, primarily due to the action of specific lactic acid bacteria (LAB) strains. The process is influenced by fermentation time, flour type, and the LAB strains present in the sourdough starter.

Key Points

Sourdough Reduces Oxalates: Lactic acid bacteria (LAB) present in sourdough can break down oxalates, significantly lowering their content in fermented foods.
Time is Key: Longer, slower fermentation processes allow more time for LAB to degrade oxalates and other antinutrients like phytic acid, enhancing mineral absorption.
Flour Matters: The amount of oxalate reduction depends on the initial oxalate content of the flour. Whole grain flours are higher in oxalates than refined flours.
Microbial Variety: The effectiveness of oxalate degradation varies depending on the specific strains of LAB and wild yeast present in a sourdough starter.
Enhanced Digestibility: In addition to reducing oxalates, sourdough fermentation improves the bioavailability of minerals and pre-digests gluten, making bread easier to digest.

The Science Behind Sourdough Fermentation and Oxalates

Sourdough is created through a natural fermentation process involving a symbiotic culture of wild yeast and lactic acid bacteria (LAB). This process, unlike rapid commercial yeast fermentation, takes place over an extended period, allowing for a number of biochemical changes to occur in the dough. It is the activity of these LAB strains that is crucial for breaking down antinutrients like oxalates.

Lactic acid bacteria are known to produce enzymes, and some strains possess specific enzymes, like oxalyl-CoA decarboxylase, that enable them to degrade oxalic acid. This is not a universal trait of all LAB, but many strains, particularly those found in traditional fermented foods, have demonstrated this capability. As these bacteria thrive in the dough, they consume carbohydrates and produce lactic and acetic acids, which create an acidic environment. This acidic state, along with the specific enzymes, facilitates the breakdown of antinutrients.

Factors Influencing Oxalate Reduction

Several factors determine the extent to which sourdough fermentation can reduce oxalate levels in bread:

Fermentation Time: The duration of the fermentation is a critical factor. Longer fermentation times generally lead to a more significant reduction in antinutrients. The extended period allows the LAB more time to act on the flour, breaking down compounds like phytic acid and, potentially, oxalates. Bread made with a quick, commercial yeast method does not undergo this prolonged process and thus retains higher levels of these compounds.
Type of Flour: The oxalate content of the final bread depends heavily on the flour used. Whole grain flours, which include the bran, naturally contain higher concentrations of oxalates and phytic acid than refined white flour. While sourdough fermentation can reduce these levels, a whole wheat sourdough loaf will still likely contain more oxalates than a white flour sourdough loaf. Using low-oxalate flours like buckwheat or rice flour is another strategy, particularly for those on a strict low-oxalate diet.
Microbial Composition: The specific strains of wild yeast and LAB in a sourdough starter can vary greatly. Some starters may have more potent oxalate-degrading strains than others, leading to different levels of reduction. The consistency and health of the starter play a significant role in its ability to effectively degrade antinutrients.

Sourdough vs. Commercial Yeast Bread

To understand the benefits of sourdough, it's helpful to compare its fermentation process with that of standard commercial yeast bread.

Comparison of Anti-Nutrient Reduction


Aspect	Sourdough Bread	Commercial Yeast Bread
Fermentation Process	Slow, natural fermentation (12-48+ hours) using wild yeast and lactic acid bacteria.	Rapid fermentation (1-2 hours) using a single, commercial yeast strain.
Oxalate Reduction	Significant reduction in oxalates possible due to specific LAB strains.	Minimal reduction, as the quick process does not allow for microbial breakdown.
Phytic Acid Reduction	Highly effective reduction of phytic acid, significantly increasing mineral bioavailability.	Less effective; a much lower percentage of phytic acid is broken down.
Mineral Absorption	Higher bioavailability of minerals like iron, zinc, and magnesium due to phytic acid breakdown.	Lower bioavailability of minerals due to high remaining phytic acid content.
Digestibility	Often easier to digest for some individuals due to pre-digestion of gluten and starches.	Can be harder to digest for sensitive individuals due to intact gluten and phytic acid.

Other Health Benefits of Sourdough Fermentation

Beyond reducing antinutrients, sourdough fermentation offers several other health advantages:

Improved Mineral Absorption: The breakdown of phytic acid, or phytate, is one of the most well-documented benefits of sourdough. Phytic acid, found in the bran of whole grains, binds to minerals like calcium, iron, and zinc, making them less available for the body to absorb. Sourdough's acidic environment activates the enzyme phytase, which degrades phytic acid, freeing up these essential minerals.
Lower Glycemic Index: Sourdough bread has a lower glycemic index (GI) compared to regular bread. This means it causes a slower, more gradual increase in blood sugar levels, preventing the sharp spikes and crashes associated with high-GI foods. The acetic and lactic acids produced during fermentation are responsible for this effect by slowing down starch digestion.
Enhanced Digestibility: The long fermentation process pre-digests some of the complex carbohydrates and proteins, including gluten, in the flour. This partial breakdown can make sourdough bread easier to digest for many individuals with mild gluten sensitivity, though it is not suitable for those with celiac disease.
Gut Health Support: While the baking process kills most of the probiotics, the fermentation can enrich the bread with prebiotics, which are food for the beneficial bacteria already in your gut. This can promote a healthier balance of gut flora and overall digestive wellness.

Practical Implications for a Low-Oxalate Diet

For those managing their oxalate intake, choosing sourdough bread, especially from a long-fermented process, can be a beneficial strategy. However, it is not a complete solution. The starting oxalate level of the flour is a major determinant of the final product's content. Therefore, using lower-oxalate flours and choosing a long-fermented sourdough technique provides the greatest benefit. Combining sourdough fermentation with other processing methods, such as soaking or sprouting grains before baking, could further enhance antinutrient reduction, though research specifically on oxalates in sourdough bread is more limited than for phytic acid.

For more detailed research, a 2001 study on mineral bioavailability compared sourdough and commercial yeast fermentation: Prolonged fermentation of whole wheat sourdough reduces phytate level and increases soluble magnesium

Conclusion

In conclusion, sourdough fermentation does have the ability to break down oxalates, but the extent of this reduction is dependent on several factors, including the specific LAB strains in the starter and the duration of fermentation. It is a powerful tool for reducing antinutrients and increasing the bioavailability of minerals, especially compared to bread made with commercial yeast. For those looking to reduce their oxalate intake, opting for long-fermented sourdough made with lower-oxalate flours can be a positive step. While not a cure-all, incorporating sourdough into your diet is a flavorful and nutritionally beneficial choice for many individuals.

Frequently Asked Questions

Yes, sourdough bread, particularly when made with refined white flour and a long fermentation process, is generally considered suitable for a low-oxalate diet. Traditional fermentation reduces antinutrients, but it is not an exhaustive solution, and the flour type matters greatly.

Sourdough fermentation significantly reduces antinutrients like oxalates and phytic acid compared to commercial bread. The rapid process of commercial yeast bread leaves these compounds largely intact.

Yes, sourdough is highly effective at breaking down phytic acid. The lactic acid bacteria in the starter activate the phytase enzyme, which degrades phytic acid and improves the body's ability to absorb essential minerals.

While sourdough fermentation reduces oxalates in whole wheat flour, the initial concentration in the bran and germ is so high that the final bread still contains a higher level of oxalates than refined white flour sourdough. For low-oxalate diets, low-oxalate grains or refined flour is preferable.

Yes, research has identified specific strains of lactic acid bacteria, including Lactobacillus plantarum and Lactobacillus fermentum, that can significantly degrade oxalates.

Yes, studies have shown that lactic acid fermentation can reduce oxalate content in other oxalate-rich foods like spinach and beetroot, suggesting the process can be applied beyond bread.

No, the baking process does not reverse the breakdown of oxalates that occurred during fermentation. The reduction happens in the dough before it is baked. The heat kills the microorganisms but does not alter the reduced antinutrient state of the final product.