Of over 300000 different plant species in the world, at least 2000 species are considered to be poisonous. Cases of poisoning are often reported when wild species of mushrooms, berries or other plants are ingested. Globally, only hundreds of plant species are commonly eaten, yet many of them can become toxic to the body if they are taken in excess or if they are not properly treated before consumption. Depending on the species, the edible parts of plants vary, which may include foliage, buds, stems, roots, fruits and tubers, and so are their poisonous parts.

Natural toxins

• They are naturally present in plants & animals.
• The long term ingestion of natural toxins in commonly eaten foods that risks to human health.
• Usually, natural toxins are not acutely toxic, except in a few cases in animals.
• Most of the natural toxins, particularly those occurring in plant-derived foods, induce adverse effects only after chronic ingestion or by allergic reactions.

Types of toxicants in plants

The toxic in plants may be classified on the basis of their chemical structure, the specific action they bring about or their biosynthetic origin. Although this classification does not encompass all the known groups of toxin, it does present the list of those frequently found in human food, in general the toxic substance in plants are :

• Enzyme Inhibitor
• Physiological Disorganizors
• Alterations of Hormonal Actions
• Antivitamins
• Antimetabolites

Methods of reduction of plant toxins

Method of reduction of plant toxins usually natural toxins will only be harmful if consume them in large quantities over a long period of time but you can help to reduce the amount you eat by doing the following things:

Advice to trade

• Store potatoes in a cool, dry and dark environment. Avoid keeping stocks for prolonged periods.
• Display a smaller stock at any one time.
• Discard stocks that show signs of sprouting, greening, physical damage or rotting.
• Do not use sprouting, greened or damaged potatoes for making food products.

Advice to public purchase

• Avoid buying potatoes that show signs of sprouting, greening, physical damage or rotting.
• Buy foods from reputable sources and do not patron illegal hawkers.
• Do not eat vegetables and fruits raw or undercooked if they are usually consumed cooked.


• Remove potatoes from plastic bags and place them in a cool, dry, and dark place at home.
• Store only small amounts of potatoes at home.
• Discard potatoes that show signs of sprouting, greening, physical damage or rotting.

Preparation and consumption


Avoid eating potatoes that show signs of sprouting, greening, physical damage or rotting.

Cyanogenic plants

• Cutting the cyanogenic plants into smaller pieces and cook thoroughly in boiling water to release toxic hydrogen cyanide before consumption helps reduce the level of the toxin. Since hydrogen cyanide is volatile, it is easily removed by open-lid cooking.
• When the cooking method chosen is heating under dry-heat or at low moisture contents, limit the intake of the cyanogenic plants to only small amounts.

For other vegetables

• Cook beans such as green beans, red kidney beans and white kidney beans, cassavas, bamboo shoots thoroughly at boiling temperature after thorough soaking in clean water.
• Do not use raw or inadequately-cooked green beans or other bean species in the preparation of salad dishes. Always bear in mind a few raw beans can cause food poisoning symptoms.
• When eating fresh fruits, avoid eating seeds of fruits, such as apples, apricots, pears, etc., whereas the flesh of these fruits is nutritious and safe to eat.
• Store potatoes in a dark, cool and dry place and avoid eating potatoes that show signs of greening, sprouting or rotting.
• Limit the intake of the ginkgo seeds to not more than a few seeds per day and avoid eating uncooked seeds, especially for children.

Take a balanced and varied diet containing plenty of fruits and vegetables as they are nutritious and safe to eat after observing the above risk avoidance or reduction measures.


Natural toxins are found widely in edible plants which are otherwise nutritious and beneficial to health. These food plants can be consumed if suitable measures are taken, such as careful selection, adequate processing and cooking, and limitation of intake.

The public is reminded to follow the health advice of maintaining a balanced and varied diet, including a wide variety of fresh fruits and vegetables, as they are nutritious and safe to eat after observing the above advice.


1. Abara, A.E. (2003). Tannin content of Dioscorea bulbufera. J. Chem. Soc. Niger 28: 55-56.

2. Agbair, P.O. (2012). Levels of anti-nutritional factors in some common leafy edible vegetables of southern Nigeria. African Journal of Food Science and Technology 3(4): 99-101.

3. Chattoo, M.A. and Khan, S.H. (2011). Anti-nutritional factor in vegetables. Rashtriya Krishi 6(1): 9-11

4. Igile, G.O. (1996). Phytochemical and Biological studies on someconstituents of Vernonia amygdalina (compositae) leaves. Ph.D thesis, Department of Biochemistry, University of Ibadan, Nigeria.

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