August 2026 - Anti-Nutrients: The Dark Side of Plants

Metabolic Medical

August 2026 Newsletter

All life has some means of self-protection. As animals, we humans are well equipped through physical means to run, punch, scratch, bite, kick and scream in our own defence. Plants don’t have the luxury of much motion so they resort to chemical defences. In nature, there are far many more poisonous plants than there are poisonous animals. None of us would randomly eat plants in the woods for fear of toxicity.

I was blessed to have a Mum who was well educated in health and nutrition. As Mum prepared rhubarb every spring to celebrate the beginning of warmer weather, she would warn me to never eat a rhubarb leaf because of its deadly oxalate content. Oxalate is so powerful it is used as a popular rust remover and cleaning agent. This protective wisdom to be mindful of the risk of plants was passed to me as an introduction to anti-nutrients. Yet the word “anti-nutrient” was never mentioned in four years of medical school. It took my own suffering and decades of practice, witnessing chronic pain, anemia and countless kidney stone patients before I drew the connection.

Even among our “safe” fruits and vegetables, these anti-nutrients lurk: chemical metabolites made by the plant to defend against pests and disease. These chemical shields protect the plant’s tissues, seeds, and offspring. In nutrition and medicine, many anti-nutrients are actually classified as phytonutrients or antioxidants. However, anti nutrients can present a threat to human health if consumed in large amounts or over an extended time.¹ The diseases of anti nutrients tend to develop gradually. Humans have devised ways to decrease the toxicity of some anti nutrients, lessons learned through acute poisonings, hunger and experimentation. Boiling, soaking, sprouting and fermentation have all been used to make toxic plants, like cassava, safer to eat. But these methods merely reduce the anti nutrients, they don’t eliminate them. Conversely, juicing, low calcium diets, dehydration, intestinal inflammation and dysbiosis can increase the body’s absorption and toxicity of these powerful chemicals.

Although plants may contain many types of anti-nutrients, there are four broad categories. There are anti-nutrients which may bind minerals, preventing their absorption and leading to mineral deficiencies of iron, magnesium, zinc or calcium. Some may inhibit enzymes, decreasing the activity of critical digestive enzymes like protease and amylase. Other anti- nutrients like lectins and saponins work by creating injury to membranes, leading to intestinal permeability. And some anti-nutrients directly disrupt our hormones and nerve function. The goitrogen anti-nutrients, found in cruciferous vegetables such as broccoli, cauliflower and cabbage, block iodine uptake for the thyroid. Some antinutrients can work through multiple mechanisms. Let’s briefly explore the three most common anti-nutrients: phytates, lectins and oxalates.

Phytates and lectins are both found in some of the most consumed foods on earth: whole grains, legumes, nuts and seeds. Phytates make up the outer germ of many plants. By binding to calcium, zinc, iron and magnesium, phytates decrease our absorption of these minerals, reducing their bioavailability. Bread has a lot of phytates. In 1958, Dr Ananda Prasad suspected zinc deficiency in a 21 year old man who appeared to be 10 years old.² The patient consumed 90% of his calories from bread. The phytate anti-nutrient had locked up critical zinc. Zinc is essential for estrogen, progesterone, testosterone and human growth hormone. Prasad subsequently identified other cases and published his findings. By limiting bread and introducing food rich in zinc- meat, eggs and dairy- teenage boys grew rapidly. Dr Prasad became known as “the father of zinc biology” by proving zinc is essential for human growth.³

Lectins are sticky proteins found in the skin and seeds of plants. When consumed in large quantities, lectins can cause severe intestinal damage, leading to increased intestinal permeability.¹ They can also stimulate the production of antibodies, leading to food allergies.¹ This is part of the reason why nightshade plants (potatoes, tomatoes, peppers, eggplant) cause so much inflammation for people living with autoimmune illnesses, specifically inflammatory bowel disease.

Oxalates are perhaps the best known anti-nutrient because of the oxidative stress and inflammation they create. They are found in a wide variety of foods: potatoes, sweet potatoes, beets, spinach, kale, almonds, raspberries and chocolate. Not only do they bind minerals in the intestines, leading to deficiencies, but their structure makes them highly inflammatory. Oxalates are crystals and their shape predicts their danger. This affects every tissue they touch: intestines, blood vessels, kidneys, joints and nerve tissue. Oxalates disrupt the lining of the intestines, increasing intestinal permeability (leaky gut) and drives up oxalate blood and tissue levels. Medicine has known (and sadly forgotten) for almost 200 years that oxalates cause intestinal inflammation and GI dysfunction. This inflammatory crystal also interacts with the immune system of the GI tract and can trigger autoimmune conditions. As they travel through our blood vessels, oxalates injure the inner lining (endothelium) like little knives, increasing the risk of atherosclerosis. And as the body tries to clear the toxin through the kidneys, oxalates can accumulate to form kidney stones. Over 80% of kidney stones are calcium oxalate from dietary oxalate. In a 2023 review, the mechanism of oxalate-induced renal injury was speculated to occur from immune system activation creating inflammation, fibrosis and scarring.⁵ Oxalates also directly damage nerves through inflammation, mineral depletion and mast cell activation. By depleting the brain and nerve’s ability to produce energy, oxalates have been implicated in a wide variety of neurological and psychological symptoms, especially chronic pain.⁴

We have mechanisms for detoxifying oxalates. In our intestinal microbiome, Oxalobacter formigenes break down oxalate. However, two thirds of adults have lost their O. formigenes from antibiotic use or excess oxalates.⁴ And although we have mechanisms for clearing up to 200mg of oxalates daily⁴, this can easily be overwhelmed by eating multiple high oxalate foods and especially with juicing. One spinach smoothie can have more than 1000mg of oxalate, completely overwhelming the detoxification mechanisms. Acute poisoning from oxalate happens with 3000-4000mg of oxalates.⁴

Medicine has never learned about anti-nutrients therefore doesn’t connect them to disease. Recurrent kidney stone patients are often not taught to reduce their oxalate consumption. They keep coming back. But what about the anemic patients? Those with chronic pain? In medicine and society, plants have been granted a halo of virtue where we emphasize their benefits and ignore their potential risks. These dogmatic associations have left many of us eating backwards, neglecting what’s essential and filling up with foods that have hidden dangers. I fell into both the vegetarian and vegan traps in an ill informed quest to improve my health and autoimmune illness, ulcerative colitis. Eliminating meat and eating exclusively plants made me anemic, anxious and inflamed. Although I was aware of the vitamins, minerals and fiber of the fruits and vegetables I was consuming, I had neglected a component that was never listed on the “nutrition facts:” the anti-nutrients.

Interestingly, meat contains no anti-nutrients. Ruminants such as cows eat anti-nutrients found in grass and grain and detoxify them through fermentation. Meat is the original and reigning superfood.

People often ask me why I don’t eat plants. Despite many years of an animal based, ketogenic diet where I was also eating fruits and vegetables, I was still dependent on medication to control the symptoms of colitis. Once I stopped taking in plants with their antinutrients and fiber, I turned down the inflammation.

My disease went into remission.

I was able to stop taking pills.

And who wouldn’t want that?

References:

1. Samuel Ariyo Okaiyeto, Dan Liu, Cheng Zhang, Jun-Wen Bai, Chang Chen, Piyush Sharma, Arun Prasath Venugopal, Ebenezer Asiamah, Hilary Kwesi Ketemepi, Franker Amen Imadegbor, Oduye Temitope Gabriel, Weiqiao Lv, Hong-Wei Xiao Anti-nutrients of plant-based food: physicochemical properties, effects on health and degradation techniques- a comprehensive review Journal of Future Foods 2025 ISSN 2772-5669

2. Sandstead HH. Human zinc deficiency: discovery to initial translation. Adv Nutr. 2013 Jan 1;4(1):76-81. doi: 10.3945/an.112.003186. PMID: 23319126

3. Toshiyuki Fukada Late Prof. Dr. Ananda Prasad “The legend and the father of zinc biology” Journal of Trace Elements in Medicine and Biology, Volume 80, 2023, 127276

4. Norton, S. K. (2023). Toxic superfoods: How oxalate overload is making you sick—and how to get better. Rodale Books.

5. Bao D, Wang Y, Zhao MH. Oxalate Nephropathy and the Mechanism of Oxalate-Induced Kidney Injury. Kidney Dis (Basel). 2023 Jul 27;9(6):459-468. doi: 10.1159/000533295. PMID: 38089442