You may have already seen the Bottom Line article about oxalate, a compound in most plant-based foods and one that can cause kidney stones. But kidney stones may be just the tip of the iceberg, according to Sally K. Norton, MPH, a nutrition consultant and educator and an oxalate researcher.

It almost sounds like a trick by Mother Nature. Oxalate is found in foods we think of as extremely healthy, foods ranging from spinach and Swiss chard to almonds to chia seeds, yet it’s often called an anti-nutrient because it limits your body’s ability to absorb good-for-you minerals, especially calcium.

Norton emphasizes the diversity of oxalate’s forms and harmful effects. They come in foods both as as sharp-edged crystals that can irritate your gut and as smaller molecules that can be absorbed and travel around the body. In addition to causing direct toxic effects when absorbed, oxalates can bind minerals and build up in nearly every type of body tissue, such as bones, tendons, joint fluid, skin, and especially the kidneys. But this is not widely known, even among researchers.

These deposits in your body can grow more damaging over time. In your kidneys they can turn into those painful kidney stones. Getting more, not less, calcium in your diet can actually help you avoid these stones, allowing the calcium to bind the oxalate and reduce how much you absorb in the first place.

AN UNRECOGNIZED PROBLEM

Many health care professionals believe that all plant foods are good for you, says Norton, and that other than causing kidney stones in some people predisposed to them, oxalates aren’t a problem. But eat enough of them, and they can lead to a range of health issues.

A kidney stone can cause obvious symptoms such as intense pain. Signs of oxalate accumulation in other areas aren’t as obvious, said Norton. There’s no single set of symptoms that point to having too many oxalates in your system. But, she added, there are clusters of problems that, for many people, improve when they carefully cut back on oxalate consumption.

Consider limiting your intake of foods containing oxalate if you experience two or more of the following…

Repeated kidney infections

Urine that’s often cloudy

Irritable bladder with frequent urination

GI problems such as leaky gut, constipation or diarrhea

Joint pain that comes and goes without obvious cause or that affects different parts of your body on different days

Persistent or recurring back stiffness or pain

Difficulty getting restful sleep and feeling fatigued because of it

Cognitive issues such as brain fog, memory loss or poor concentration

Sensitive or achy teeth without infection or cavities

Persistent or lingering symptoms after an injury or operation

If you’ve had bariatric surgery, a malabsorption syndrome, or chronic gut inflammation, you’d be wise to watch your oxalate consumption. All these conditions cause excessive absorbtion of oxalate, Norton says.

PUTTING A LIMIT ON OXALATE

Norton explains that a safe level of oxalate in food depends on how healthy a person’s kidneys and digestive tract are. If you don’t have any health issues, a safe limit might be as high as 200 to 300 mg a day. Otherwise, you’d be smart to cap oxalates at 150 mg per day or less. A low oxalate diet is usually defined as 50 mg per day or less.

To give you an idea how quickly you can get into high levels of oxalate, consider this sample from Norton’s “worst offenders” list:

Rhubarb, 1,000 mg in one-half cup stewed or canned

Swiss chard, 900 mg in one-half cup

Cooked spinach, 500 mg in one-half cup

Chia seeds, 380 mg in one-quarter cup

Baked white potato, 120 mg in one medium

Almonds, 115 mg per ounce (20 nuts)

Other high-oxalate foods include cashews, peanuts, beets, okra, soy, pinto beans, black beans, figs, kiwi, prunes, bran cereals, chocolate, black or green tea and the spices turmeric and cumin. Norton adds that vitamin C can turn into oxalate in the body, so supplementing with more than 250 mg of C per day could make an oxalate problem worse.

No one need give up on plant foods. If you eat a lot of high oxalate foods and have symptoms that could be due to oxalates, try some smart substitutions. Safer yet very nutritious veggies include cabbage, cucumbers, lettuce, radishes, pumpkin seeds, squash and turnips. Heating does not remove oxalate from foods. However, boiling can leach out some of the oxalate.

Norton suggests learning more about oxalate toxicity at two non-profits that focus on conditions that could be worsened by high oxalate intake, the VP (Vulvar Pain) Foundation and the Autism Oxalate Project’s Trying Low Oxalate Group that helps families use the low-oxalate diet (click on Find the Support Group).