Types of Natural Toxins in Food and Their Effects

Not all food dangers come from bacteria or chemicals added during processing. Many common foods – especially plant-based ones – contain natural toxins that have evolved as defense mechanisms. These are compounds produced by plants and animals as part of their normal biological processes. When consumed in significant quantities or without proper preparation, these toxins can interfere with digestion, damage red blood cells, or even cause paralysis. Understanding them is key to both food safety and good nutrition.

What are natural toxins in food? 🔗

Natural toxins are toxic compounds produced by living organisms such as plants, fungi, and certain animals. According to the World Health Organization (WHO), these substances are not harmful to the organisms that produce them but can be toxic to humans when eaten. Plants often produce them as a defense against insects, predators, or microbial infections. They are classified as secondary metabolites – meaning they are not involved in basic growth or energy production but serve protective or signaling roles for the organism.

Common categories of natural plant toxins include protein inhibitors, cyanogenic glycosides, saponins, toxic amino acids, and glycoalkaloids. Animal-origin toxins (such as those from shellfish or certain fish) also exist but are outside the scope of this discussion. Here, we focus on plant-derived toxins that are especially relevant to everyday foods like pulses, legumes, and beans.

Trypsin inhibitors in pulses 🔗

Trypsin inhibitors are proteins found abundantly in raw legumes such as soybeans, kidney beans, lima beans, and peas. Trypsin is a digestive enzyme produced by the pancreas that breaks down dietary proteins into smaller, absorbable peptides. When trypsin inhibitors are present in food, they bind to this enzyme and block its activity, impairing protein digestion.

The consequences of consuming significant amounts of trypsin inhibitors include poor protein absorption, digestive discomfort, and in chronic cases, pancreatic enlargement as the organ works harder to compensate for the inhibited enzymes. This is why eating raw or undercooked soybeans and kidney beans can cause digestive distress.

How to reduce trypsin inhibitors 🔗

The good news is that trypsin inhibitors are heat-sensitive. Proper cooking at high temperatures – especially boiling or pressure cooking – can significantly reduce their activity. Soaking legumes overnight and then boiling them vigorously for at least 10 minutes is a well-established method to neutralize these compounds. This is precisely why traditional cooking practices across cultures have always emphasized thorough cooking of pulses and beans before consumption.

Cyanogenic glycosides: the hidden cyanide risk 🔗

Cyanogenic glycosides are among the most dangerous natural toxins found in food plants. These compounds are present in over 2,000 plant species and release hydrogen cyanide (HCN) when the plant tissue is damaged – through chewing, cutting, or digestion. Foods known to contain them include cassava, lima beans, bamboo shoots, sorghum, bitter almonds, flaxseed, and the seeds of stone fruits like apricots, cherries, and peaches.

The mechanism is straightforward. In intact plant tissue, cyanogenic glycosides are stored separately from the enzymes that break them down. When the tissue is disrupted (for example, during chewing), the enzyme and substrate come together, releasing HCN. According to a review published in IntechOpen, exposure to cyanide through improperly processed cyanogenic plants can lead to acute poisoning, growth retardation, and neurological damage affecting the central nervous system.

Cassava: a major concern 🔗

Cassava is a staple food for hundreds of millions of people, particularly in Africa and parts of Asia. It contains the cyanogenic glycoside linamarin, found throughout the tuber, while the enzyme that breaks it down – linamarase – is concentrated in the peel. When cassava is peeled, cut, or damaged, the two come into contact and produce HCN. Bitter cassava varieties contain especially high levels of the toxin. Traditional preparation methods such as prolonged soaking, fermenting, and thorough boiling have evolved specifically to reduce cyanide to safe levels.

Symptoms of cyanide poisoning 🔗

The WHO notes that clinical signs of acute cyanide poisoning include rapid breathing, a drop in blood pressure, dizziness, headache, vomiting, mental confusion, and convulsions. In severe cases, death can result when the cyanide level exceeds the body’s ability to detoxify it. The key preventive measure is proper processing – cutting cyanogenic foods into small pieces and cooking them thoroughly in water allows volatile HCN to escape.

Saponins: the soapy troublemakers 🔗

Saponins are a group of compounds named after the Latin word “sapo,” meaning soap, because they produce a soapy foam when mixed with water. They are found in a wide range of plants including soybeans, quinoa, chickpeas, and tea leaves. Saponins serve as natural defense chemicals for the plant, deterring herbivores and protecting against microbial infections.

When consumed in large amounts, saponins can irritate the gastrointestinal lining, causing nausea, vomiting, and diarrhea. They can also affect cell membranes and, in high doses, may damage red blood cells – a property known as hemolytic activity. However, at moderate dietary levels, some saponins are also being studied for potential health benefits, including cholesterol-lowering effects.

Washing quinoa thoroughly before cooking is a common practice specifically to remove the saponin-rich outer coating. Similarly, soaking and boiling legumes helps reduce saponin content to safe levels.

Lathyrism: the paralysis from kesari dal 🔗

One of the most devastating examples of food-borne toxicity is lathyrism, a neurological disease caused by the excessive consumption of Lathyrus sativus, commonly known as kesari dal (grass pea or chickling pea). This hardy legume thrives in drought conditions where other crops fail, making it a survival food for poor communities in parts of India, Bangladesh, and Ethiopia.

The neurotoxin ODAP (BOAA) 🔗

The toxic agent in kesari dal is β-N-oxalyl-L-α,β-diaminopropionic acid, commonly abbreviated as ODAP or BOAA. This is a non-protein amino acid that acts as a structural mimic of the neurotransmitter glutamate. When consumed in large amounts over weeks or months, ODAP overstimulates nerve cells, leading to their damage and death – a process called excitotoxicity.

Symptoms and irreversibility 🔗

Neurolathyrism typically manifests as spastic paraparesis – a progressive stiffness and weakness of the legs, leading to difficulty walking and, in severe cases, complete paralysis of the lower limbs. The condition is irreversible. Early symptoms include cramping in the calf muscles, increased muscle tone, and an abnormal gait. Young adult men who perform heavy physical labor appear to be most vulnerable, possibly because of higher consumption levels and increased metabolic demands.

The disease typically develops when kesari dal constitutes more than 30% of the daily diet over a prolonged period. Historical outbreaks have been documented in India’s Madhya Pradesh, Uttar Pradesh, and Bihar, as well as in Ethiopia during famines. Some Indian states have banned the sale of Lathyrus seeds to prevent consumption.

Prevention strategies 🔗

ODAP is water-soluble. Soaking the dal overnight and discarding the water before boiling can remove up to 90% of the toxin. Roasting at 140°C for 15-20 minutes also reduces neurotoxin levels significantly. Eating kesari dal as part of a mixed diet (rather than as the sole staple) and combining it with legumes rich in sulfur-containing amino acids also lowers risk. Scientists have also developed low-toxin varieties of Lathyrus sativus through selective breeding, offering hope for safer cultivation.

Favism: when broad beans attack red blood cells 🔗

Favism is a condition triggered by the consumption of broad beans (fava beans), scientifically known as Vicia faba, in individuals with a genetic deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD). This enzyme normally protects red blood cells from oxidative damage. When it is deficient, certain compounds in fava beans can cause the red cells to rupture – a process called hemolysis.

The toxic compounds: vicine and convicine 🔗

Fava beans contain the β-glucosides vicine and convicine. In the gut, these are metabolized into divicine and isouramil, which are potent oxidizing agents. In a person with adequate G6PD, the enzyme generates enough NADPH to neutralize these oxidants. But in G6PD-deficient individuals, red blood cells cannot cope with the oxidative stress, and they break down rapidly.

Symptoms and who is at risk 🔗

Favism presents as acute hemolytic anemia – symptoms include sudden onset of jaundice (yellowing of the skin), dark-colored urine, fatigue, rapid heartbeat, and an enlarged spleen. In severe cases, especially in children, favism can be life-threatening. According to the American Society of Hematology, favism remains one of the most common causes of acute hemolytic anemia worldwide.

G6PD deficiency is an X-linked genetic condition, making males more commonly affected. It is estimated to affect 400-500 million people globally, with particularly high prevalence among populations of Mediterranean, African, Middle Eastern, and Southeast Asian descent. Importantly, the compounds vicine and convicine are relatively heat-stable and are not destroyed by cooking, which makes avoidance the primary prevention strategy for affected individuals.

Other notable natural toxins in food 🔗

Lectins (haemagglutinins) 🔗

Lectins are proteins found in many legumes, with red kidney beans containing the highest concentrations. They can bind to the lining of the intestine, interfere with nutrient absorption, and cause red blood cells to clump together. Eating as few as four or five raw or undercooked kidney beans can cause severe nausea, vomiting, and diarrhea. Like trypsin inhibitors, lectins are destroyed by thorough soaking followed by vigorous boiling for at least 10 minutes.

Glycoalkaloids in potatoes 🔗

Potatoes contain natural toxins called solanine and chaconine, which are types of glycoalkaloids. These are found at higher concentrations in green, sprouted, or damaged potatoes. Unlike many other natural toxins, glycoalkaloids are not destroyed by cooking. The best preventive measure is to avoid buying or consuming potatoes that have turned green or begun sprouting, and to store them in a cool, dark, and dry place.

Why proper food preparation matters 🔗

A common thread running through nearly all plant-based natural toxins is that traditional food preparation methods – soaking, fermenting, boiling, peeling, and discarding soak water – evolved precisely to deal with these hazards. These are not arbitrary cultural practices; they are time-tested safety measures developed over generations of observation and experience.

For toxins like trypsin inhibitors, lectins, cyanogenic glycosides, and ODAP in kesari dal, heat and water are effective deactivators. For glycoalkaloids in potatoes and vicine/convicine in fava beans, avoidance of affected produce or awareness of genetic susceptibility is the key. A balanced, varied diet – rather than heavy reliance on a single food – naturally limits exposure to any one toxin.

What do you think? Were you aware that so many everyday foods contain natural toxins? How do your family’s traditional cooking practices – like soaking pulses overnight or discarding soak water – relate to the science of toxin removal?

References

1. https://www.who.int/news-room/fact-sheets/detail/natural-toxins-in-food
2. https://www.cfs.gov.hk/english/multimedia/multimedia_pub/multimedia_pub_fsb_201501.html
3. https://e-safe-project.eu/topics/topic-1-natural-toxins/
4. https://www.intechopen.com/chapters/52207
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC3767245/
6. https://www.sciencedirect.com/topics/medicine-and-dentistry/lathyrism
7. https://en.wikipedia.org/wiki/Lathyrism
8. https://www.ncbi.nlm.nih.gov/books/NBK532498/
9. https://ashpublications.org/thehematologist/article/doi/10.1182/hem.V15.2.8304/463044/Deconstructing-the-Threat-of-the-Fava-Bean
10. https://www.sfa.gov.sg/food-safety-tips/food-risk-concerns/risk-at-a-glance/the-arch-enemy-of-g6pd-deficient-individuals-fava-beans