By Sally K Norton, MPH

Liam Hemsworth publicly blamed spinach smoothies for a 2019 kidney stone episode that required surgery.

In 2020, Men’s Health magazine quoted Liam as saying, “Last year, I was feeling really low and lethargic. And then I got a kidney stone.” He added, “Every morning I was eating five handfuls of spinach followed by almond milk, almond butter, and some vegan protein in a smoothie. And that was what I considered super healthy. So, I had to completely rethink what I was putting into my body.”

Even moderate, relatively common levels of oxalate in a habitual diet can fuel the customary aches and pains of life: digestive distress, inflamed joints, chronic skin issues, brain fog or mood problems, and health declines associated with “normal” aging. And then there are those painful kidney stones. Eighty percent of them are formed from oxalate, much of which comes from the foods we eat.

Background

For a great majority of plants, oxalic acid and oxalate crystals are essential to their growth, reproduction, and survival. As a defense to keep from being eaten, plants use oxalic acid’s toxic powers to shun a variety of predators, such as infectious fungi and insects. 

In an ancient technique, central and southern African hunters harnessed the power of oxalic acid by driving wooden arrowheads into banana tree trunks about twenty-four hours before the hunt. The oxalic acid in the tree sap is a powerful enough nerve toxin to paralyze prey. 

Oxalate crystals in foods are harder than teeth and can cause tooth wear in humans. It’s no wonder that they may also cause irritation to the mouth and digestive tract. Typically, we don’t experience sensations in our mouth from the crystals in foods because we don’t grind up the plant cells enough while chewing. However, when we pulverize foods—turning them into nut milks, for example—we not only free crystals to abrade the digestive tract but we’re also setting oxalic acid free and enhancing its ability to do us harm. Almond milk, being a dilute solution of pureed and filtered almonds, contains high concentrations of bioavailable oxalates that readily move into the bloodstream.

Oxalate Overload Symptom Profile

Because it is so easy to overeat oxalates, chances are you may already be experiencing occasional oxalate-related aches and pains. Do you tend to get a stiff neck? In those of us with dietary oxalate overload, issues such as pain, knots, or stiffness in the top of the shoulders or in the upper or lower back are typical. Some people experience chronic or intermittent joint inflammation, gout, arthritis, carpal tunnel syndrome, or a more generalized stiffness, often accompanied by a lack of pep.

Other seemingly small signs and symptoms can be indicators of oxalate overload, including itchy or dry eyes, floaters, excessive tartar on the teeth, tooth sensitivity, sensitive or frail skin, and odd discomforts, such as pressure or pain in the loins, irritable bladder, urinary tract infections, frequent urination, or crystalluria.

Crystalluria

Chronically cloudy urine is a visible sign of high levels of oxalate crystals, a condition called crystalluria. Crystal-laden urine is a risk factor for kidney disease, yet it typically gets little attention by medical health professionals.

Oxalate Content in Common Foods

Plants are living things and their oxalate content can vary substantially depending on factors such as growth environment, metabolism, and varietal genetics. Even the stage of maturity can be important. For example, a very ripe Hass avocado has only about 7 mg of oxalate, yet a firm one that is barely ripe contains about 50 mg—seven times as much.

As another example, black and white peppercorns used in everyday cooking are the fruit of the same pepper vine, but their oxalate content is quite dissimilar. The black peppercorn is picked when unripe and is high in oxalate (~13 mg/teaspoon). In contrast, the white peppercorn is picked when fully mature and is very low in oxalate. 

Interestingly, nightshades (Solanaceae family), including potatoes, tomatoes, and eggplant, tend toward higher oxalate content, but they vary considerably. Ripe red peppers (bell and hot) are often low in oxalate, yet green, yellow, and orange bell peppers are two or three times higher.

Fresh tomatoes are generally “medium-high,” depending on variety (and portion size). While having a few tomato wedges on a salad is fine on a low-oxalate diet, tomato sauce and other concentrated forms of tomatoes are considered high-oxalate foods and need attention to portion sizes. Typically, concentrating the foods by cooking or drying them increases their density and the amount of oxalate they contain. For instance, a 1/2 cup of boiled spinach has a lot more spinach (and oxalate) than a 1/2 cup of raw spinach.

Here’s one helpful tip: sometimes knowing the plant family to which a food belongs can suggest whether that food is likely to be very high or very low in oxalates (or relatively unpredictable). Plant foods that are relatively low in oxalates come from the following two families: 

• The cabbage family (Brassicaceae or Cruciferae), includes broccoli, cauliflower, arugula, collards, mustard, kale, watercress, radish, turnips, rutabaga, and other common vegetables. 
• True lettuces (Asteraceae family), including butterhead, romaine, iceberg, and leaf varieties.

A Lesson in Poor Data

Like cauliflower, turnip and rutabaga are members of the brassica family. They are low in oxalate and can easily substitute for potatoes. Peeled baking potatoes—Russet and Idaho—have 25 to 50 mg oxalate per 100 grams; boiled red skinned new potatoes are lower in oxalate; a small number of tests suggest they have about 20 mg per 100 grams.

Cooked turnip contains only 2 mg of oxalate per ½ cup, according to testing done at the University of Wyoming. But if you didn’t know turnips are brassicas, you’d be fooled by some poorly published data available online.

In a list hosted by the Harvard School of Public Health Nutrition Department, and widely circulated online, their data claim that turnips have fifteen times that amount of oxalate (30 mg). That’s probably a decimal point error, but it illustrates a key reason as to how using online data can be confusing. Evaluate your source of information and check it carefully for accuracy.

Indeed, you can trust the brassicas to provide bioavailable minerals. They are a flexible culinary family that can not only fill in for potatoes but also be a substitute for chard and spinach as a side dish or be added to enrich soups, stews, and casseroles. Just use the brassicas in moderation and make sure they are properly prepared; they are harder to digest when raw or undercooked.

Safe Consumption

The amount of oxalate humans can consume without ill effect, while variable, is surprisingly low. Kidney researchers suggest that a “normal” and safe intake level is within the range of 150 to 200 mg/day. “High-oxalate” eating—with great potential to get healthy people into trouble over time—is typically defined as 250 mg or more per day. Diets over 600 mg/day are considered “extremely high.”

In healthy populations, a diet under 200 mg/day is likely low enough to avoid oxalate problems (about 60 mg oxalate per meal). This intake level offers recovery potential for mild kidney problems and symptom relief. In fact, relief from oxalate-related symptoms may be just five to ten days away when oxalate intake is consistently lowered. All you need is a bit of sustained attention, and you’ll see that it’s doable.

Top Four Offenders

The following oxalate content data are summarized from test results reported by reputable laboratories and research reports:

Spinach, raw—Serving: 1 ½ cups (45 g) / Oxalate Per Serving (mg): 450-500

Chia seeds—Serving: ¼ cup (40 g) / Oxalate Per Serving (mg): 260

Almonds, with skins—Serving: 24 nuts (28 g) / Oxalate Per Serving (mg): 120

Sweet potato, baked, flesh only—Serving: 1 cup (200 g) / Oxalate Per Serving (mg): 100-150

Path to Recovery

It is quite feasible to get better from oxalate overload just by reducing your oxalate intake, but because so many of us are deficient in essential minerals and even vitamins, it may be worth also considering supplements and other lifestyle adjustments. 

Sauna and Cold Therapy. Inconsistent blood flow in the small vessels can slow your healing and get you stuck in chronic pain. Thermal therapies are an effective and inexpensive support for improving your blood flow and lowering any inflammation. 

Heat exposure in particular, such as through sauna therapy, activates the sweating process in a relaxed state and can gently and safely help eliminate toxic substances of all kinds, including oxalate. A hot sauna opens and stimulates blood flow, improving delivery of nutrients and oxygen to the tissues, with benefits that are similar to exercise (but with less energy expenditure). As one researcher put it, “Sauna treatment may be, in effect, a lazy person’s exercise with regard to health improvement.” 

Likewise, ice packs and even cold showers are therapeutic for pain and can be mood-boosting. Take a 3-minute cold shower following sauna to re-energize.

Citrates for Lowering Acidity. Oral intake of citric acid (citrate) is a well-established, highly effective, and well-tolerated treatment for kidney stones. Whether the source is a supplement, food additive, or lemon juice, citric acid is helpful for getting the oxalate safely out of the body. The citrate sticks to and softens oxalate crystals. Citrate also increases the protective effects of other anti-clumping molecules in the urine. Citrate may help you feel better because it also protects against oxalate-induced oxidative stress and corrects acidic conditions that can cause malaise. 

Citrate also promotes strong bones and teeth, and, together with potassium in the context of a low oxalate diet, may stop or even reverse the loss of bone in osteopenia, osteoporosis, and other disorders of bone fragility. Meanwhile, the liver turns some citrate into bicarbonate, which stimulates the kidney cells to release and excrete protective citrate into the urine.

Lemons

Lemons, as citrus fruits, are an excellent source of citric acid and citrate. Several studies have demonstrated that about 1/2 cup of lemon juice daily is nearly as effective in reducing kidney-stone recurrence as potassium citrate treatment. Lemons are also very helpful in addressing the acidosis that accompanies oxalate clearing and other inflammatory states. 

To use fresh lemons therapeutically, consume at least two per day. Take them straight or as hot lemonade (with hot water and an optional touch of sweetener). Lemon juice is my favorite supplement because it is so effective as first aid for any ailment! It is safe to consume lemon juice frequently. Although citrate has the power to strengthen teeth and improve mineralization, protect your teeth from the acid in lemon juice by sipping plain water afterward. 

Use your own saliva and tongue to wipe traces of the lemon away, then swallow. For your teeth’s sake, avoid sipping acidified water all day. (That’s one reason I recommend “lemon juice shots.”) As one client commented, “I’ve been drinking straight lemon juice four to six times per day for two years, and my teeth are great—not a single cavity!”

Vitamins and Minerals. Supplemental vitamins and minerals help correct nutrient deficiencies and may lower the amount of oxalate produced in the body. Supplements can also help ease the symptoms and side effects of oxalate de-accumulation. For example, when your body is struggling with chronic inflammation, leaky gut, and oxalate overload, you will need adequate calcium. Sources include milk (~280 mg per cup), cheese (~200 mg per ounce), and bones (3 ounces of sardines have ~300 mg). 

Thoughtful, moderate supplementation, when combined with a diet of high quality, digestible, nutrient-dense food (that is ample in protein and low in oxalic acid), is the most effective route to correct a chronic nutrient shortfall and to rebuild lasting health.

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Sally Norton, MPH, received her bachelor’s degree in nutritional science from Cornell University and her master’s degree in public health from the University of North Carolina, Chapel Hill.

Well Being Journal adapted the above excerpt from Toxic Superfoods copyright © 2022 by Sally K Norton. Used by permission of Rodale Books, an imprint of Random House, a division of Penguin Random House LLC, New York. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.