March 11, 2023

If you’ve known anyone who’s had a kidney stone, you’d know that they are debilitating.

Kidney stones cause excruciating pain and would be often considered “the worst pain” someone has felt.

Kidney stones are small, hard deposits of oxalic acid crystals in the kidneys.

There are many factors that can contribute to the formation of kidney stones. One of the most significant factors is the presence of oxalates in the diet.

Oxalates are naturally occurring compounds found in a variety of plant-based foods, primarily leafy greens, vegetables, nuts, and seeds. These compounds bind with calcium in the body, forming crystals that can accumulate and develop into kidney stones.

It’s important to be aware of the top oxalate-containing foods and reduce their consumption.

One way people may consume an excessive amount of oxalates are through green smoothies.

It’s commonly thought that “green smoothies” are healthy to eat. I’m not really convinced that green smoothies are that healthy. A lot of the greens people use can contain HUGE amounts of oxalates. Eating these foods in large quantities every day may increase your risk for kidney stones. Please consider the following:

Top Oxalate-Containing Foods:

Swiss chard – 1 cup of cooked Swiss chard contains approximately 962 mg of oxalate. Swiss chard is often billed a “superfood.”

Soybeans – 1 cup of cooked soybeans contains approximately 755 mg of oxalate (maybe skip the edamame next time).

Spinach – 1 cup of raw spinach contains approximately 656 mg of oxalate. Spinach is a very popular source of “greens” in green smoothies.

Rhubarb – 1 cup of cooked rhubarb contains approximately 541 mg of oxalate.

Almonds – 1 oz of almonds (approximately 23 almonds – a very small amount) contains approximately 183 mg of oxalate.

Quinoa – 1 cup of cooked quinoa contains approximately 177 mg of oxalate.

Beets – 1 cup of raw beets contains approximately 164 mg of oxalate.

Chocolate – 1 oz of dark chocolate contains approximately 95 mg of oxalate.

Sweet potatoes – 1 cup of cooked sweet potatoes contains approximately 46 mg of oxalate.

In order to understand the dangers of oxalate-containing foods, it is important to consider the thresholds of consumption that relate to unhealthy oxalate consumption. According to a study published in the Journal of Urology, consuming more than 250 mg of oxalate per day increases the risk of kidney stone formation (1). However, this threshold can vary depending on individual factors such as age, sex, and overall health.

Thresholds of Oxalate Consumption

Another study found that women who consumed more than 400 mg of dietary oxalate per day had a 44% higher risk of developing kidney stones than those who consumed less than 150 mg per day (2).

In addition to dietary oxalates, urinary oxalate levels can also be affected by other factors such as vitamin C supplementation and dehydration. The vitamin C in virtually all supplements is in the form of ascorbic acid. Ascorbic acid is metabolized into oxalate in the body, and dehydration can limit oxalate excretion. If you want vitamin c in your diet, I recommend eating some fruits rather than supplementing with vitamin C. Fruits contain healthy compounds such as flavonoids and other anti-oxidants that aren’t present in ascorbic acid.

Reducing the Risk of Kidney Stones

If you’re concerned about the risk of kidney stones, there are several steps you can take to reduce your risk. First, it is important to limit your consumption of high-oxalate foods, particularly if you have a history of kidney stones or want to avoid the possibility of kidney stones.

This may involve reducing your intake of foods such as spinach, swiss chard, and almonds, or finding alternative sources of these nutrients that are lower in oxalates. If you’d like to eat these foods I recommend eating them in smaller quantities and certainly not stuffing a smoothie with them.

Additionally, increasing your water intake can help to dilute the concentration of oxalates in the urine, reducing the risk of stone formation. Aim to drink at least 64 ounces water per day, and more if you’re physically active or live in a hot climate.

Sources for oxalate content in food:

Medical College of Wisconsin Kidney Stone Oxalate Diet

USDA Food Composition Database:

Harvard T.H. Chan School of Public Health’s Nutrition Source:

1. Siener, R., & Hesse, A. (2013). The effect of different diets on urine composition and the risk of calcium oxalate crystallisation in healthy subjects. The Journal of urology, 189(1), 158-163. doi: 10.1016/j.juro.2012.08.094

2. Taylor, E. N., Curhan, G. C., & Fung, T. T. (2007). DASH-style diet associates with reduced risk for kidney stones. Journal of the American Society of Nephrology, 18(11), 3020-3025.

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