Toxic Constituents in Plant Foods

Organic Food

Nature has given plants the ability to synthesize materials that are toxic which protect them from predators such as fungi, insects, animals, or humans. There are several plant foods which contain naturally occurring toxins. If we look at the number of people reacting adversely to naturally occurring toxin’s they may outnumber people who show allergic reactions (1).

Apart from natural toxins formed in food as defense mechanisms of plants, they can be formed through because of infestation with toxin-producing microorganisms (2).


There are different types of plant toxins occurring in nature

Protease inhibitors

Soybeans contain a protease inhibitor that inhibits the enzyme trypsin. Protease inhibitors are widely distributed throughout the plant kingdom, especially in legumes, and to a lesser extent in cereal grains and tubers. Because of these compounds, protein is not completed digested. Soybeans and soy products when adequately heat treated the trypsin inhibitor is inactivated and are safe for consumption.


Most legumes and cereals contain a protein that has the ability to agglutinate red blood cells that is it makes the red blood cells to clump together. These proteins are called lectins or phyto-hemagglutinins or lectins. Some of these lectins are extremely toxic. Lectins are found in many foods including soybeans, tomatoes, bean sprouts, raw vegetables, fruits, spices, dry cereals, and nuts but they are not toxic. Boiling legumes like red kidney beans for about 10 minutes takes care of lectins.


Lathyrism is a paralytic disease that is associated with the consumption of Lathyrus sativus. Lathyrogen is a metabolic antagonist of glutamic acid, which is involved in the transmission of nerve impulses.


A number of plants contain glycosides from which hydrogen cyanide may be released because of enzymatic hydrolysis. The most common plants eaten by humans which contain glycosides in order of their glycoside content, are: lima beans, sorghum, cassava, linseed meal, black eyed pea, garden pea, kidney bean, Bengal gram and red gram.


These are substances that have potential of causing goiter. These are found in plants belonging to the cabbage family, including cabbage, turnip, broccoli, cauliflower, Brussel sprouts, kale, rape seed, and mustard seed. Goiter is the enlargement of thyroid gland.

Other natural toxins

There are several other natural toxins present in plant foods such as saponins, solanidines, lupin alkaloids, mimosine, mycotoxins to name a few.

According to WHO when it comes to natural toxins it is important to understand that they are present in a variety of different crops and foods.  If you are consuming a healthy and balanced diet, the levels of natural toxins are well below the threshold for acute and chronic toxicity.

Adverse health effects of natural toxins can be acute poisoning ranging from allergic reactions to severe stomach ache and diarrhoea, and even death. Long-term health concerns include effects on the immune, reproductive or nervous systems, and also cancer.

To minimize the health risk from natural toxins in food, the steps taken are (2)

  • Don’t assume that if something is natural it is automatically safe
  • Get rid of bruised, damaged or dis-coloured food, and especially mouldy foods
  • Discard any food that does not smell or taste fresh, or has an unusual taste
  • Eat mushrooms or other wild plants that are identified as non-poisonous.


  1. David, J. (2005) Food Intolerance. In: Caballero, B., Allen, L. and Prentice, A. (eds). Encyclopaedia of Human Nutrition. Elsevier Academic Press. Pp 300-309.
  2. World Health Organizations (2019) Natural toxins in food

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