PDF Summary:Toxic Superfoods, by Sally K. Norton

Many people think of foods like spinach, almonds, and sweet potatoes as nutritious staples of a healthy diet. But according to Sally K. Norton in Toxic Superfoods, these seemingly healthy foods contain high levels of oxalates—compounds that can accumulate in your body and cause serious health problems. Norton explains that oxalates can trigger inflammation, deplete essential minerals, and contribute to conditions ranging from kidney stones to joint pain and digestive issues.

In this guide, you'll learn how oxalates damage your body at the cellular level, why oxalate toxicity is so difficult to diagnose, and which common foods contain the highest levels of these compounds. Norton provides strategies for transitioning to a low-oxalate diet, including how to identify problematic foods, which cooking methods can reduce oxalate content, and how to make dietary changes gradually to avoid triggering uncomfortable symptoms as your body releases stored oxalates.

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Let’s look at some symptoms and risk factors of oxalate-related toxicity.

Symptoms of Excess Oxalates

Norton explains that oxalate toxicity can cause a wide range of symptoms, including joint discomfort, exhaustion, and digestive issues. These symptoms can be delayed, variable, and changeable, making them difficult to trace back to oxalate-related toxicity. Oxalate toxicity can also cause nerve damage, leading to anxiety, depression, migraines, and cognitive issues. Additionally, it can cause spasticity of muscles and nerves, which may result in acid regurgitation, problems swallowing, too much burping, and hiccoughs.

(Shortform note: If you have fibromyalgia, you may experience many of the symptoms Norton describes, but they’re likely not due to oxalate toxicity. Fibromyalgia is a chronic condition characterized by widespread pain, fatigue, and cognitive difficulties. The exact cause of fibromyalgia is unknown, but it’s believed to involve abnormal pain processing in the central nervous system. This condition can lead to a variety of symptoms, including muscle stiffness, sleep disturbances, and digestive issues. While fibromyalgia can cause significant discomfort and impact daily life, it’s not related to oxalate toxicity.)

Norton adds that oxalate toxicity can cause dermatological issues such as redness, dry skin conditions, and shedding. It can also lead to eye problems, including sties, deposits, redness and sensitivity in the eyelids, and vision issues. Furthermore, oxalate toxicity can cause problems with hearing and balance, such as ringing in the ears, dizziness, and a condition known as Ménière's disease. It can also cause pelvic issues like genital pain, vulvar discomfort, and sexual dysfunction. Lastly, it can cause problems with urination, including stones in the kidneys, calcified kidneys, urinating too frequently, an urgent need to urinate, painful burning sensations, bladder inflammation, bladder pain from burning, urethral pain, lack of urinary control, urinating in bed, murky urine, and urine that contains sediment or a powdery substance.

(Shortform note: According to encyclopedia editors, Ménière's disease is a chronic disorder of the inner ear that causes recurring attacks of vertigo, hearing loss, tinnitus, and a feeling of fullness in the ear. The exact cause of Ménière's disease is unknown, but it is believed to be related to abnormal regulation of endolymphatic fluid in the inner ear. This fluid is essential for normal sensory function in the inner ear, but when it builds up, it can disrupt the delicate balance of the inner ear and lead to the symptoms of Ménière's disease.)

Risk Factors & Diagnostic Considerations

The amount of oxalate in food varies significantly, making it difficult to estimate intake accurately. Norton explains that a plant's oxalate levels depend on its genetics, how it was grown, and how mature it is. For instance, a ripe Hass avocado contains roughly seven milligrams of oxalate, whereas an unripe one has around 50 mg. The way foods are prepared also affects their oxalate levels. Cooking or dehydrating foods increases their oxalate density. Oxalate levels in foods can additionally be influenced by contamination from oxalate-producing molds, such as Aspergillus and Penicillium.

(Shortform note: The variability in oxalate content in plants has been a subject of scientific inquiry for decades. In a research article published in 1987, researchers reviewed the literature on oxalate in crop plants, discussing the factors that influence oxalate accumulation and the implications for human health. The authors noted that oxalate content varies widely among plant species and even within different tissues of the same plant. They also discussed the role of calcium oxalate crystals in plant physiology, suggesting that these crystals may serve as a means of regulating calcium levels within plant cells. This early research laid the groundwork for our current understanding of oxalate in plants and its potential impact on human health.)

These molds are often found in flour and products made from wheat. In addition, oxalic acid is sometimes used to reduce discoloration of leafy greens while in storage. Norton adds that the lack of reliable information on foods' oxalate levels makes it difficult to estimate your oxalate consumption. Serving sizes are often vague, and food densities can vary. Examining foods' oxalate content is tricky, and researchers often fail to specify the variety, maturity, and other characteristics of the foods they test. This leads to poor-quality data that complicates recognizing oxalate overload. Norton suggests employing approximations to gauge your oxalate consumption. Base your meals on trustworthy information about the contents of foods, and reduce your consumption of untested or highly variable foods.

How to Approximate Your Oxalate Consumption

To work around the lack of reliable information on foods' oxalate levels, you can approximate your exposure by basing your meals on plant tissues that researchers have found to store fewer calcium oxalate crystals. For example, a research article on the formation and function of calcium oxalate in plants suggests that many fleshy fruits have lower oxalate levels than other plant tissues. This is because the plant’s reproductive tissues are often more sensitive to oxalate than other tissues, so the plant stores less oxalate in these tissues. In addition, you can treat mature leaves and seed brans as oxalate-dense whenever you encounter them. This is because plant biologists have found that these tissues are often used to store excess oxalate.

Dietary Strategies & Supportive Therapies

Food Choices & Oxalate Load

Norton recommends choosing low-oxalate alternatives when cooking. Extracts utilized in baking or cooking typically have low oxalates, so you can use them to replace high-oxalate spices. Starches like cornstarch and potato starch have minimal oxalates and serve as thickeners. However, not all white thickeners in powdered form are processed starches. Potato flour, arrowroot, and tapioca starch are unrefined and contain large amounts of oxalates. The amount you eat plays an important role in how much oxalate you consume. If you enjoy foods that are spicy or highly seasoned, they can significantly contribute to your oxalate intake.

(Shortform note: If you have a medical condition that requires you to limit your intake of certain foods, you may find it difficult to follow Norton’s advice. For example, if you have diabetes, you may need to limit your intake of carbohydrates, which are found in many of the low-oxalate alternatives Norton recommends. This is because carbohydrates can raise your blood sugar levels, which can be dangerous for people with diabetes. In this case, you may need to find a balance between limiting your oxalate intake and managing your diabetes. For example, you may need to limit your intake of pungent seasonings, even though they are low in oxalates, because they can also raise your blood sugar levels.)

The most problematic spices are black pepper, turmeric, and cumin. Herbs like basil and parsley also have elevated oxalate content. According to Norton, eating habits in the West rely heavily on refined flours. Flour is an ingredient in breads, buns, pasta, macaroni, noodles, crackers, couscous, cookies, pastries, and cold cereals, and it's also used for thickening gravies and sauces. Proteins from wheat (and other lectins) can cause digestive discomfort and may not be suitable for people harmed by oxalates. All kinds of wheat items, and most gluten-free alternatives, contain oxalates.

(Shortform note: If you don’t have a disease related to oxalates and you use these ingredients in small amounts, you may not need to worry about their oxalate content. Whole-diet analyses show that black pepper, turmeric, cumin, basil, and parsley contribute only a small amount to total oxalate intake. Similarly, while refined flours are a major part of Western diets, their oxalate content is relatively low compared to other foods. Most gluten-free alternatives are also low in oxalates.)

Items composed of refined wheat can contribute significant oxalate levels, particularly given their limited nutritional value. Store-bought white sandwich loaves made with refined white flour have between 6 and 7 milligrams of oxalate in each slice. Whole-grain breads contain roughly twice the oxalates of white-flour breads. Commercially produced whole wheat bread has 15 to 20 mg of oxalate per slice. Norton explains that multigrain breads can contain differing levels of ingredients rich in oxalates, including poppy and chia seeds, nuts, and the grains teff, buckwheat, and quinoa. The oxalate content can be 50 mg per slice or more. Non-wheat and gluten-free breads differ greatly in how much they depend on ingredients high in oxalates like starch from cassava, whole rice, potato-derived flour, bran from rice, starch from the arrowroot plant, and nut meal. Avoid low-carb almond bread.

(Shortform note: The Dietary Guidelines for Americans 2020-2025, published by the US Department of Agriculture and the US Department of Health and Human Services, recommends regular consumption of grain foods, especially whole-grain products such as breads. The guidelines state that “healthy dietary patterns include grains, with at least half of total grain intake coming from whole grains.” The guidelines recommend that adults consume six ounces of grains per day, with at least three ounces coming from whole grains. The guidelines also recommend that children and adolescents consume three to eight ounces of grains per day, with at least half coming from whole grains. The guidelines state that whole grains are a good source of fiber, vitamins, and minerals, and that they can help reduce the risk of chronic diseases such as heart disease, type 2 diabetes, and certain types of cancer.)

Pastas are a major category of wheat flour products. Certain macaroni and noodle products have been found to contain higher oxalate levels than you'd expect based on their white-flour base. A cup of cooked Mueller's Elbow Macaroni contains around 40 milligrams of oxalate, whereas the tricolor type contains 50 milligrams. A serving of cooked Mueller's brand Thin Spaghetti measuring one cup contains 20 milligrams of oxalate.

(Shortform note: The 1999 review by Noonan and Savage included a table of oxalate content in processed wheat foods, including pasta, that was compiled from various studies. The values they reported for these foods were in the same general range as the values Norton reports for Mueller’s pasta products. This suggests that the values Norton reports are likely based on direct chemical measurements of oxalate content in these foods.)

Squash spaghetti, a veggie replacement for gluten-based pasta, contains approximately 9 milligrams per cooked cup. Gluten-free pasta choices that have less oxalate include shirataki noodles (made from konjac), cellophane (bean thread) noodles, and white rice noodles, both Asian. A popular way to consume wheat-based processed foods is by having breakfast cereal. A half-cup of All-Bran cereal contains roughly 75 mg of oxalates, whereas a 50 gram portion of shredded wheat contains approximately 40 mg. Eating 9 to 11 servings of highly refined wheat flour every day—as the 1992 USDA Food Pyramid suggested for two decades—provides a substantial amount of oxalate: 60 mg to over 300 mg each day. Those with severe oxalate-related health issues often benefit most by cutting out gluten grains during their recovery.

(Shortform note: The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) doesn’t recommend cutting out gluten grains for those with oxalate-related health issues. Instead, they suggest limiting high-oxalate foods like spinach, rhubarb, and almonds, and balancing calcium intake to reduce oxalate absorption. They also recommend drinking plenty of water, limiting sodium and animal protein, and maintaining a healthy weight. The NIDDK’s approach focuses on moderation and balance rather than complete elimination of certain food groups.)

Norton explains that boiling can lower oxalate content. Boiling, then throwing out the cooking liquid, will extract varying levels of soluble oxalate. Boiling foods with moderate oxalate levels, such as ginger and asparagus, can be helpful. Raw ginger contains 10 mg per tablespoon, but the crystallized version has very little oxalate because it's boiled for an hour, the water is thrown away, and then it's cooked and covered in sugar. Cooking fresh broccoli in boiling water for twelve minutes will lower the oxalate levels by half or more.

(Shortform note: If you’re eating broccoli or ginger for their other health benefits, boiling them for a long time may not be the best option. For example, food scientists have found that boiling broccoli for 10 minutes can reduce its vitamin C content by 50%. Vitamin C is a powerful antioxidant that helps protect your cells from damage. Broccoli also contains glucosinolates, which are compounds that may help prevent cancer. However, boiling broccoli for 10 minutes can reduce its glucosinolate content by 60%. If you’re eating broccoli for its vitamin C and glucosinolate content, you may want to consider steaming or microwaving it instead of boiling it.)

However, it's pointless to boil foods that are very high in oxalates; despite extended boiling, oxalate levels drop but stay quite elevated. Norton adds that soaking isn't effective. It's unproven that soaking nuts and seeds decreases their oxalate content. Actually, soaking could cause nuts, beans, and grains to have more soluble oxalate, as the seed draws on calcium as it sprouts. It’s helpful to soak grains—even those with lower levels of oxalate—to eliminate plant toxins like phytates, but it doesn’t get rid of oxalate. In most cases, lacto-fermentation is also ineffective at reducing oxalate content.

(Shortform note: Contrary to Norton’s claim that soaking and lacto-fermentation are ineffective at reducing oxalate content, researchers have found that these methods can be effective. In a research article, nutrition researchers reviewed studies on the oxalate content of foods and its effect on humans. They found that soaking and lactic fermentation can reduce the oxalate content of certain foods. For example, soaking taro leaves in water for 18 hours reduced their total oxalate content by 20%. Lactic fermentation of taro leaves for 72 hours reduced their total oxalate content by 40%. Soaking and lactic fermentation can also reduce the oxalate content of other foods, such as spinach, amaranth, and rhubarb. However, the effectiveness of these methods depends on the type of food, the soaking or fermentation time, and the temperature.)

Fermenting with lactic acid bacteria—a process used to make foods like yogurt, sauerkraut, kimchi, and dill pickles—has been proven to break down a portion of the oxalates present in the end product, compared to their levels in raw form. However, the ingredients used to make these fermented foods generally contain low oxalates. Fermenting leafy greens with high oxalate levels doesn't significantly reduce their oxalate amounts. In a six-day fermentation process, amaranth greens experienced a 10% reduction in oxalate levels, while spinach decreased by 14%, from 894 mg to 773 mg per 100 grams. A traditional Hawaiian food called poi—a starchy paste made mainly from cooked taro—is often fermented for one to two days, which reduces the oxalate content by ~18 percent, from 86 mg per 100 grams (unfermented) to 70 mg per 100 grams.

How Lactic Acid Bacteria Break Down Oxalates

According to medical researchers, lactic acid bacteria can break down oxalates because they contain a specific enzyme that allows them to use oxalates as a source of energy. This enzyme enables the bacteria to transport oxalate into their cells, where it’s broken down into smaller molecules that the bacteria can use for energy and to regulate their internal pH. This process not only helps the bacteria survive in acidic environments but also reduces the amount of oxalate in the food they ferment. A research article published in 2005 found that a specific strain of lactic acid bacteria, called Lactobacillus acidophilus, was particularly effective at breaking down oxalates. This strain was able to reduce oxalate levels by up to 70% in a laboratory setting.

Implementing and Supporting a Low-Oxalate Meal Plan

To implement a low-oxalate diet, Norton recommends making changes gradually. A sudden shift from eating a lot of oxalates to having very few can cause your body to release oxalate too quickly, leading to unpleasant symptoms. To avoid this, decrease your oxalate intake in two phases. In the first phase, lower how much oxalate you consume to a moderate amount and maintain it for a while. In the second phase, further reduce the amount of oxalate you consume to a low level and maintain that amount.

(Shortform note: To make these two phases a habit, try linking a specific low-oxalate food swap to an existing routine. For example, if you usually have a spinach salad for lunch, replace it with a lettuce salad. This way, you’ll automatically make a healthier choice without having to think about it.)

According to Norton, success depends on maintaining consistency. The primary advantages develop gradually as you adhere to the diet, so think about the long run and anticipate a gradual healing process. Avoid frequently starting and stopping a low-oxalate diet, as taking a large dose of triggers at the wrong time might spike oxalate levels and throw the clearing process out of balance. Whether you plan to or not, straying from the diet might lead to uncomfortable and long-lasting effects. Norton advises against allowing yourself to become overly hungry, as this will unnecessarily challenge your self-control and resolve, making it especially tough to resist the oxalate-rich foods that form old habits.

(Shortform note: While consistency is important for any diet, it’s possible to take it too far. In Health Food Junkies, Steven Bratman and David Knight describe how the pursuit of dietary health can become an obsession, leading to a condition known as orthorexia nervosa. This condition is characterized by an unhealthy fixation on eating only “pure” or “correct” foods, often at the expense of overall well-being. Bratman and Knight explain that orthorexia can lead to nutritional deficiencies, social isolation, and a constant state of anxiety about food choices. They emphasize that when dietary rules become rigid and all-consuming, they can undermine the very health they’re meant to protect. This perspective suggests that while consistency in a low-oxalate diet may be beneficial, it’s equally important to maintain flexibility and avoid letting dietary restrictions dominate your life.)

You'll avoid feeling deprived by getting sufficient nutrients and calories, so ensure you eat enough during meals. Continue learning and growing. Try new foods and recipes to expand your palate and your culinary talents. Numerous people who follow a low-oxalate diet have told Norton that after sticking with it for a while, they experience severe negative effects from foods high in oxalate, as though they have developed an additional "sensitivity" to oxalate. Norton identifies four or more factors that contribute to increased "sensitivity" to foods high in oxalates once you've begun a low-oxalate diet:

(Shortform note: Fredric L. Coe, a kidney-stone specialist, and his coauthors take a different stance on the idea that a low-oxalate diet makes people more “sensitive” to foods high in oxalate. They argue that restricting oxalate is a useful tool for people who form kidney stones, but they don’t mention that people who follow a low-oxalate diet become more “sensitive” to oxalate. Instead, they explain that oxalate restriction is a tool that can be used to reduce the risk of kidney stones in people who are prone to them. They also note that oxalate restriction is not necessary for everyone, and that it can be difficult to follow a low-oxalate diet.)

1. Now that you're aware, you're noticing and identifying how what you eat affects your well-being. 2. Once you've adjusted to eating less oxalate, you might absorb it somewhat more—potentially 14 percent instead of 8 percent—meaning that if you're not prepared for it, a food high in oxalate might affect you more strongly. 3. Your body might be fully occupied eliminating oxalate. Norton recommends starting a low-oxalate diet in a way that’s genuine, meticulous, and comprehensive. Following this plan will reveal its worth to you. In moments of uncertainty, self-doubt is natural, but patience is crucial. Trust that your system can adjust with proper nutrition, a steady reduction in your toxic load, and sufficient sleep. Trust that your regular habits will contribute to your future well-being. Put your faith in a higher power and in your natural abilities.

The Dangers of Obsessive Healthy Eating

Norton’s advice to follow a meticulous, comprehensive plan and trust the process may be problematic for some people. According to researchers, a fixation on healthy eating can lead to orthorexia, a condition where people become obsessed with eating only foods they consider healthy. This obsession can lead to malnutrition, social isolation, and emotional distress. Some clinicians argue that orthorexia should be recognized as a distinct eating disorder, as it shares similarities with anorexia nervosa and obsessive-compulsive disorder. A literature review suggests that orthorexia is characterized by an excessive focus on food quality and purity, leading to restrictive eating patterns and impaired daily functioning. The review highlights the need for further research to better understand the prevalence, risk factors, and effective treatments for orthorexia.