Food Oxalates: How to Reduce Oxalate Levels for Better Health

by Arpi Gasparyan | Last updated on February 19, 2024

Medically reviewed by Elen Khachatrian

Introduction

Due to the numerous dietary restrictions, adhering to a low-oxalate diet can sometimes be challenging. In some cases, medications and a low-oxalate diet may not be enough to prevent stone formation.

In this article, you will learn how to decrease food oxalate levels and absorption from the intestines. Most studies focus on soluble oxalates as they are more bioavailable and negatively impact health than insoluble ones.

Food Preparation Methods & Oxalate Changes

Various cooking techniques affect oxalate levels differently, mainly leading to oxalate loss.

Boiling & Cutting Size

Boiling leads to soluble oxalate loss due to oxalate leaching and thermal degradation (1). Over 50% of oxalates may be removed. This method of removing oxalates is effective only when the water used in boiling is not consumed (2).

In a study, spinach was cut into different sizes and boiled in water. There was a positive association between the cutting size and oxalate reduction, with narrower pieces leading to greater oxalate removal. The results showed that cutting spinach into 1cm pieces and boiling it in water for 2 minutes at 100°C led to up to 72% oxalate loss (2).

The table below shows oxalate changes in some foods before and after boiling. The foods were boiled in water until reaching a soft consistency: 12–15 minutes for vegetables and 2 hours for beans (3).

	Before Boiling (mg/100g)	After Boiling (mg/100g)
Spinach	978 ± 5	477 ± 8
Carrot	49 ± 7	16 ± 9
Beetroot	67 ± 12	52 ± 14
White bean	158 ± 16	47 ± 17
Red bean	113 ± 15	72 ± 17
Soybean	497 ± 22	224 ± 25

In a study, boiling Japanese taro cormels reduced the soluble oxalate levels in the cooked tissues below the detectable levels (3).

Soaking & Blanching

If the food is eaten raw, it can be soaked in water to remove oxalates by leaching.

For example, soaking the seeds of peas, lentils, chickpeas, fava beans, and common beans in distilled water significantly decreased total oxalate concentrations by 17 to 51% (4).

Blanching, with similar mechanisms to soaking and boiling, will also lead to oxalate loss.

Baking

Different studies show different results regarding baking and subsequent oxalate changes. A study demonstrated that baking foods increased oxalate levels due to the concentrating effects (1). Several other studies showed that baking (used only for potatoes) did not affect oxalate concentrations (5, 6).

In a study, bread doughs were baked at 160, 190, and 220 °C for 9, 12, 15, and 20 minutes to evaluate oxalate changes. Without the introduction of steam at the start of baking, higher baking temperatures and times resulted in a greater loss of oxalate due to the oxalate exposure to its melting point (7). Cooking under the steam would lead to a minimum oxalate reduction (7).

Steaming

Steaming is another cooking method where the oxalate loss can appear by leaching.

In a study, nine raw and cooked vegetable types were analyzed for oxalate; boiling resulted in the greatest reduction of soluble oxalates by 30-87%, whereas steaming resulted in 5-53% of oxalate loss (6).

Fermentation

Fermentation is frequently used in Asian countries to extend a food’s shelf life and has been reported to decrease food oxalate levels.

In a study, kimchi containing 609.32mg/100g of total oxalates was fermented for five days at 19.3 ± 0.8°C in ceramic jars with a water-airtight seal. The oxalate levels were evaluated, showing a 38.5% reduction in total oxalate levels and a 22.86% reduction in soluble oxalates (8). The effects were suggested to result from microbial or enzymatic activities during the fermentation or other factors (9).

Souring

Souring may also lead to a decrease in oxalate levels.

In a study, souring of poi (a cooked taro paste) at 20°C led to a 37% oxalate reduction. At the beginning, the oxalates were 86mg/100g, whereas by the end, they were reduced to 54mg/100g (10).

Drying

Many ingredients and foods are produced and preserved using drying or dehydration processes. Drying leads to the loss of many anti-nutrients present in food, including oxalates.

High temperatures during food drying could break down the calcium oxalate-containing cells (idioblasts), breaking the oxalate structure (9).

Cooking Methods & Food Examples

The table below shows the differences between the same samples of raw and boiled eggplant and bamboo shoots and different samples of potatoes. The table below also shows the selected foods' total and soluble oxalate distributions (1).

	Type of Sample	Total Oxalates (mg/100g)	Soluble Oxalates (mg/100g)
Eggplant	Raw	55	45
	Boiled	38	19
Bamboo shoot	Raw	222	163
	Boiled	93	51
White bean	Preserved	54.2	1.9
	Dry, seeds	547.9	38.8
Red kidney bean	Dry, seeds	74.6	4.8
Fig	Dried	95.1	5.5
Amaranth	Dried	1939.9	901.7
	Air dried	1940.8	902.3
Potato	Boiled	24.3	12.8
	Deep fried	26.9	17
	Chips	47	45.8

Ways to Decrease Oxalate Absorption

Consuming Magnesium- and Calcium-rich Foods

Since absorption of oxalates is related to soluble oxalate levels, simultaneous consumption of oxalates with calcium- or magnesium-rich foods and supplements or processing in calcium sources reduces oxalate bioavailability and absorption.

It is due to calcium and magnesium ions binding to soluble oxalates, precipitating them, and reducing soluble oxalate absorption and urinary excretion (1, 9).

According to a study, calcium carbonate reduced oxalate absorption by 5.1% and magnesium oxide by 7.6% (11).

Consuming Prebiotics and Probiotics Containing O. Formigenes

Oxalobacter formigenes is an anaerobic bacterium that degrades oxalates, preventing hyperoxaluria. Using antibiotics for anaerobic bacteria, such as metronidazole, clarithromycin, and doxycycline, may significantly reduce the bacterium levels (12).

Several probiotic and prebiotic sources, such as yogurt, kefir, and fiber-rich foods, are believed to help increase O. formigenes levels in the gut and, thus, decrease oxalate absorption.

Summary

Various cooking techniques, such as soaking, boiling, steaming, fermentation, drying, and souring, lead to oxalate loss.

Boiling is the most effective way to increase oxalate loss; over 50% can be leached and thermally degraded. Boiling the food to remove oxalates is effective only when the water is not consumed.

Different studies show different results regarding baking and subsequent oxalate changes, from leading to a decrease or having no effect on oxalate levels to increasing them.

Another way to decrease the risk of kidney stone formation is by consuming foods rich in calcium and magnesium. They reduce the bioavailability and absorption of oxalates by binding and precipitating them.

To learn why the same food has varying levels of oxalates, you may visit our “Oxalates: Why Does the Same Food Have Many Oxalate Values?” page.

References

Author name: Arpi Gasparyan

Education: General Medicine at YSMU

Last updated: February 19, 2024

Medically reviewed by Elen Khachatrian