Guest Post: The Blurry Vision of Cassava

Hello folks It is great to have you around again this Monday afternoon. Today we have another guest post for you. This piece is a researched expose on Cassava in Nigeria  by a regular guest contributor on the blog, Olufola Ige.  I hope you find it useful reading.

Cassava (Manihot esculenta Family- Euphorbiaceae) is a long tuberous starchy root about two inches around and eight inches long. The root has a brown fibrous skin and snowy white interior flesh. Cassava is native to Brazil and the tropical areas of the Americas. It was introduced to Central Africa and Nigeria by Portuguese traders in the 1500s (Fregene et al., 2000).

Cassava is classified into two major varieties, sweet or bitter. Both contain Prussic acid (hydrocyanic acid), which can cause cyanide poisoning. Cooking or pressing the root thoroughly removes the poison. Cassava should never be eaten raw. Bitter, or as some folks refer to it, wild cassava contains enough acid, that it can be fatally poisonous if eaten raw or undercooked (Akintonwa & Tunwashe, 1992).Like other roots and tubers, both bitter and sweet varieties of cassava contain antinutritional factors and toxins, with the bitter varieties containing much larger amounts. Therefore it must be properly prepared before consumption, as improper preparation of cassava can leave enough residual cyanide to cause acute cyanide intoxication (Nhassico et al., 2008), goiters, and even ataxia, partial paralysis, or death. Economically, the more toxic varieties of cassava serve as fallback resource (a “food security crop”) in times of famine or food insecurity in some places but they have to be thoroughly and processed. Some farmers also prefer the bitter varieties because they deter pests, animals, and thieves.


Cassava has immense and diverse socio-economic applications. It can be used to produce different things like flour and sugar. For example, we are bread eaters in Nigeria. The government once pushed for cassava bread, till now nothing of note has come of the issue. A percentage of cassava flour can be introduced into bread wheat instead of completely introducing it at once. Cassava bread can also be promoted itself.

The root can be made into other products which include chips, ethanol, and glucose syrup among many other uses. Such products are in high demand within and outside Nigeria and have a potential within the export arena. This will reduce the demand to import some products and also help industries that can utilize such materials grow rapidly, create jobs and other opportunities.

Confectionaries import glucose which we can get readily from cassava. Other confectionaries can make use of cassava starch to make their products. Even in pharmaceuticals it can be useful. It can be used to make ethanol. In terms of quantity cassava is the biggest produce in Nigeria, remember?

FYI, cassava can also be used to manufacture beer (Rajagopal, 1977; Dontoh & Kew 2013) –Yes; you read that right- A potential movement lies here.

The challenge of industrialization within the cassava industry lies with the reducing costs of production and transformation. This will allow for the supply of cheaper processed products of desired quality and standards to markets.

Projects can be aimed at increasing and improving the production of cassava and developing new ways to use the crop, but let us utilize what we have on ground -One step at a time-. Nigeria’s hopes of using a crop as a way to diversify the economy away from Crude Oil can be realized using this as one of the means (you might have heard this particular one over and over).

Alternatively, government can coordinate production and export of cassava chips (Kormawa and Akoroda, 2003). Like I have always maintained, “a policy is as good as its implementation” and trust me, political will is of utmost importance. It is as important as the success of the program.

Nigeria can also focus on making use of cassava as flour. This process requires availability of good processing plants which are not yet readily available. To convert cassava to flour, not a lot of processing plants do that in Nigeria so government can try to encourage people to set up plants to convert cassava to flour and also to starch.

Some years back Nigeria had a few starch processing plants and I think almost all of them folded up for one reason or the other. It was either due to a lack of produce because of the distance the product had to be transported to get there and in the process a lot of produce is destroyed before it gets to them.

The major challenge with cassava processing in Nigeria is the nature of the root itself. Cassava is perishable, from harvest, you have 48 hours to dry it up completely if not it becomes completely useless and losses its value. From the farmers’ perspective, they will rather not harvest if they don’t have buyers. This is because the available system does not encourage establishment of processing centers for cassava and other similar produce.


Another challenge is the distance and stress of transporting; bad roads, multiples taxation, several checkpoints and exploitation by transport operators makes it very difficult and unimaginably expensive to move this perishable farm produce from remote farmlands to urban cities where some of these processing centers are sparsely distributed.

Even when the produce is eventually processed, the market to sell is not readily available. Let us not begin to discuss challenges faced with exporting such products. It will seem like the system is deliberately working against you to prevent you from earning valuable foreign exchange.

Thus the farmer quickly converts his harvest into gaari or lafun so that it can be readily sold (even though it is done with a ridiculously small profit margin).

As a solution, the primary goal should be to get processors close to farmers so that cassava can be dried a bit and then they can continue with what they want to use it for so they don’t lose their produce and at the same time money invested in transporting.

That’s that about that.

Have you ever heard in the news that members of a family die after a meal of Amala?

Have you also heard of rumors that excessive consumption of gari can lead to defective eyesight?


You will now know why

Cassava root contain amounts of the cyanogenic glycosides “linamarin” and “lotaustralin”. The toxic substances may affect the liver, kidney and some parts of the brain. When the poisons are accumulated in the body, we suspect that the toxic substances in cassava may involve destroying even the optical system. To avoid exposure to the toxin, cassava should be properly prepared before eating.

Linamarin is chemically similar to sugar but contains a cyanide group. When eaten raw, the human digestive system will liberate cyanide poison. Just a few pieces of cassava roots contain a fatal dose of poison. If properly treated (in a labor-intensive process that may include roasting, soaking, or fermentation), the cyanide content is reduced significantly. The average lethal dose of cyanide for higher animals was experimentally obtained as 1 mg/kg of live weight (Oke, 1969, Cereda & Mattos, 1996). Linamarin and Lotaustralin can be catabolized to liberate hydrogen cyanide (HCN). A dose of pure synthetic linamarin (500 mg/kg) administered to rats caused clinical signs, including cardiac arrhythmias and respiratory changes and death. Similar signs were observed in rats given a single oral dose of cyanide (6 mg/kg) (Philbrick et al., 1977). Excess cyanide residue from improper preparation is known to cause acute cyanide intoxication, and goiters, and has been linked to ataxia (a neurological disorder affecting the ability to walk, also known as konzo), as well as to the tropical calcific pancreatitis in humans, leading to chronic pancreatitis. Also these cyanogenic glycosides have been linked with diabetes (Soto-Blanco et al., 2002).

Who knows, “Overconsumption of cassava products” may be one the causes of increased epidemiology of diabetes in Nigeria. “Just saying”.

The World Health Organization safe level for cyanide in cassava flour is 10 ppm (10 parts per million or 10 mg per Kg) (Cardoso et al., 2005) The total cyanide content of gari is in the range of 0-40 ppm, with an average of 20 ppm (Oke, 1994; Adindu et al., 2003) which is twice the WHO safe level of 10 ppm.

There is a high prevalence of blindness and severe visual impairment especially among those older than 40 years in Nigeria. It is estimated that more than 4.25 million adults in Nigeria older than 40 have moderate or severe visual impairment or blindness (Kwari et al., 2009)

It was reported that tropical ataxic neuropathy and some similar degenerative neuropathies that may cause poor vision occur in Nigeria mainly amongst older people who might have consumed cyanide mainly from gari over many years (Osuntokun, 1994; Nhassico et al., 2008) suggesting the effects of chronic cyanide poisoning.

Getting in to details, here is one of the mechanisms proposed; the body has several mechanisms to effectively detoxify cyanide. The majority of cyanide reacts with thiosulfate to produce thiocyanate in reactions catalyzed by sulfur tranferase enzymes such as rhodanese. The thiocyanate is then excreted in the urine over a period of days.

Although thiocyanate is approximately seven times less toxic than cyanide, increased thiocyanate concentrations in the body resulting from chronic cyanide exposure can adversely affect the thyroid.

The ‘thio’ of thiocyanate comes from the sulfur amino acids, cysteine and methionine, which are also essential to a number of vital enzymes, including glutathione peroxidase, the major natural enzyme antioxidant of cell membranes.

Thiocyanate carries similar electronic charge, size and characteristics as iodide; hence it substitutes or competes with iodide by entering the thyroid gland, and blocking the production of the thyroid hormone, thyroxine.

A low thyroid state interferes with vitamin A production, essential to regeneration of the retinal pigments and healing of the retina. Night blindness and retinal damage are the most obvious of the consequences, and vitamin A is required for healing and repair in every cell of the body.

Another way is that, as large doses of cyanide prevent cells from using oxygen, suffocation occurs at the cellular level. The nervous system is particularly vulnerable and sub-clinical cases damage the eyes and nerves. Demyelination of the brain, similar to multiple sclerosis, can also occur.

The effect of processed cassava on eyesight was confirmed in 2014 in a publication by Yusuf and colleagues (Mohammed, 2014).


Due to some challenges, cassava is quickly converted to staple food; the most common ones include Gaari, elubo(Yam Flour) and fufu, thus loading people with more starch and prussic acid. Sometimes other nutrients in a balanced diet can serve as an antidote for the chronic cyanide poisoning that may be caused by ill-prepared cassava products. Unfortunately, consumption of balanced diet has reduced due the present economic turmoil (especially for those dwelling in the urban centers with little access to fresh fruits and vegetables). This might lead to increased eye problems.

By implication, a visionless government will eventually ironically physically ruin the vision(pardon the pun) of its good people.

I rest my case.


  1. Adindu, M. N., Olayemi, F. F., & Nze-Dike, O. U. (2003). Cyanogenic potential of some cassava products in Port Harcourt markets in Nigeria. Journal of Food Composition and Analysis, 16(1), 21-24.
  2. Akintonwa, A., & Tunwashe, O. L. (1992). Fatal cyanide poisoning from cassava-based meal. Human & experimental toxicology, 11(1)w, 47-49.
  3. Cardoso, A. P., Mirione, E., Ernesto, M., Massaza, F., Cliff, J., Haque, M. R., & Bradbury, J. H. (2005). Processing of cassava roots to remove cyanogens. Journal of Food Composition and Analysis, 18(5), 451-460.
  4. Cereda, M. P., & Mattos, M. C. Y. (1996). Linamarin: the toxic compound of cassava. Journal of Venomous Animals and Toxins, 2(1), 06-12.
  5. Dontoh, E., & Kew, J. (2013). SABMiller Sells Cassava Beer to Woo African Drinkers. Bloomberg View.
  6. Fregene, M., Bernal, A., Duque, M., Dixon, A., & Tohme, J. (2000). AFLP analysis of African cassava (Manihot esculenta Crantz) germplasm resistant to the cassava mosaic disease (CMD). Theoretical and Applied Genetics, 100(5), 678-685.
  7. Kwari F, Gudlavalleti MV, Sivsubramaniam S, Gilbert CE, Abdull MM, Entekume G, Foster A (2009). Prevalence of blindness and visual impairment in Nigeria: The national blindness and visual impairment survey. Invest. Ophthalmo. Vis. Sci. 50(5) pp. 2033-2039.
  8. Kormawa, P., & Akoroda, M. O. (2003). Cassava supply chain arrangement for industrial utilization in Nigeria. Ibadan: IITA.
  9. Mohammed, N. U. H. U. (2014). Visual defects among consumers of processed cassava (gari). African Journal of Food Science, 8(1), 25-29.
  10. Nhassico, D., Muquingue, H., Cliff, J., Cumbana, A., & Bradbury, J. H. (2008). Rising African cassava production, diseases due to high cyanide intake and control measures. Journal of the Science of Food and Agriculture, 88(12), 2043-2049.
  11. Oke, O. L. (1969). The role of hydrocyanic acid in nutrition. In World review of nutrition and dietetics (Vol. 11, pp. 170-198). Karger Publishers.
  12. Oke, O. L. (1994). Eliminating cyanogens from cassava through processing: Technology and tradition. In International Workshop on Cassava Safety 375 (pp. 163-174).
  13. Osuntokun, B. O. (1994). Chronic cyanide intoxication of dietary origin and a degenerative neuropathy in Nigerians. In International Workshop on Cassava Safety 375 (pp. 311-322).
  14. Philbrick, D. J., Hill, D. C., & Alexander, J. C. (1977). Physiological and biochemical changes associated with linamarin administration to rats. Toxicology and applied pharmacology, 42(3), 539-551.
  15. Rajagopal, M. V. (1977). Production of beer from cassava. Journal of Food Science, 42(2), 532-533.
  16. Soto-Blanco, B., Sousa, A. B., Manzano, H., Guerra, J. L., & Górniak, S. L. (2001). Does prolonged cyanide exposure have a diabetogenic effect?. Veterinary and human toxicology, 43(2), 106-108.

    For more content from Olufola Ige on the blog, read Guest Post: The Butterfly Effect and A Killing that Changed The World and GUEST POST: RELIGION, THE SOCIETY AND THE HYPOCRISY OF NON MARITAL SEX

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