Toxic Plant of the Day: Cassava Root

Life lives off of life and all living things must defend themselves to survive. Plants, lacking the ability to run, have survived via biochemical warfare. This is one reason that, unlike with meat, it’s almost always better to eat plants that have been cooked or specially processed than raw, if you choose to eat them at all.

Starches became important sources of food in populations where the food we evolved to eat, high-fat meat, had been hunted to extinction, or where the culture was driven by surrounding cultures to a small area that could not support them on game alone. However, eating starches, involved arduous processing, in order to render them edible. Cassava is no exception.

Cassava (perhaps better known here as tapioca) is a starchy root. Its defence is cyanide. Like many other plants, the formation of its toxin happens when the plant cells are broken — that is, it evolved to be triggered by the bite of an insect or other animal. Cassava can be extremely toxic, especially the larger varieties. The toxicity increases under drought conditions. An ounce of a more toxic variety would be enough to kill a rat [1].

The acute response to eating it raw or insufficiently processed is vertigo, vomiting, collapsing, and possibly death. One can only imagine the desperation that we must have undergone to have found a way to eat this after such an effect. The traditional way to circumvent it is prolonged soaking, fermenting, and cooking. Contrary to the new common wisdom, fermenting became a tradition not because our gut bacteria need the resulting bacteria, but because we were using bacteria to process out toxins.

However, it isn’t always done right, and even when it is, it isn’t 100% effective. To quote some researchers who are trying to genetically modify the plant:

“Chronic, low-level cyanide exposure is associated with the development of goiter and with tropical ataxic neuropathy, a nerve-damaging disorder that renders a person unsteady and uncoordinated. Severe cyanide poisoning, particularly during famines, is associated with outbreaks of a debilitating, irreversible paralytic disorder called Konzo and, in some cases, death. The incidence of Konzo and tropical ataxic neuropathy can be as high as 3 percent in some areas.”

In a paper describing the epidemic of these neurological diseases, it is pointed out that cassava consumption has risen dramatically in the last half century, precisely because it grows well in droughts and poor soil, that condition that increases its toxicity.

“From 1965 to 2000, cassava cultivation in Africa showed an extraordinary increase, from 35 million to 90 million tons, at least partly in response to declining soil fertility and increased cost of inorganic fertilizers. For countries such as DRC, Tanzania, and northern Mozambique, cassava is the most important crop for the largest proportion of farming households [29]–[31]. The amount of labour required for cassava cultivation is considerably less than that for other crops, and this is a major reason for its promotion and increasing use in HIV/AIDS-affected communities [32].

Cassava is drought tolerant, grows on poor soils without fertilizer where no other staple can be cultivated, and generates acceptable yields even on depleted and marginal lands. Its roots may be kept in the soil for extended time periods, securing a carbohydrate source in years of agricultural crisis in poor communities, and bridging the seasonal food gap during the hungry and dry season when other crops usually fail [31], [33]. It is no surprise that in times of agricultural crisis, cassava becomes the dominant, and sometimes the only, source of food.”

They also point out that the toxic effect is worsened in protein-deficient conditions, because sulfur-rich amino acids (cysteine and methionine) are needed by a detoxifying enzyme in the liver. Animal foods are almost the only sources of these amino acids, though some nuts, spirulina, and soybeans have some.

Other cyanogenic plants include: hydrangea, flax, lima bean, apple, elderberry, white clover, and corn.


Wikipedia gives the more toxic varieties 1g/kg of cyanogenic glucosides, and says that 25 mg of pure cyanogenic glucides would kill a rat.

24 replies
  1. wjones3044
    wjones3044 says:

    I take it, then, that selective breeding for low cyanide levels has not taken place? That was the echo in my mind from biology class 20 years ago. "Sure plants don't want to be eaten but, well, selective breeding!" Of course not everything can be undone by selective breeding. Wish I had a lab and good lab minions to answer these and other questions. Also: will simply baking a cassava root detoxify it? I suspect not or people wouldn't take the time to soak and ferment.

    This post also takes me back to botany class…the discussions we had about plants' "feelings"….at the time, there was fairly new research showing that oak trees release volatile chemicals during herbivory, ostensibly signalling other leaves on the tree to produce defense compounds. We joked how our vegetables were screaming at us, just on a wavelength we couldn't hear. (No science behind the screams, but the oak leaves research was real…)

  2. L. Amber O'Hearn
    L. Amber O'Hearn says:

    Given the apparent epidemic, it appears it is not being selected out. Nor is the arsenic affinity of cruciferous vegetables.

    There is a lot of fascinating research about the nerve-like systems in plants. They feel it.

  3. Galina L.
    Galina L. says:

    I remember seriously offending a vegan lady who was raving in a lunch room how she got a life energy (another mysterious nutrient besides antioxidants) by eating alive plants, while meat eaters only harmed themselves consuming a dead flesh. I told that I considered my way of eating killed things to be more humane. May be my smooth , rosy and a wrinkles-free face was an additional offence to a gray-faced cranky vegetarian.
    Probably, the good reason for humans to consume toxic plants could be the control over intestinal parasite population. People with higher tolerance to some plants warfare agents got an evolutionary advantage, especially in hot climates. We love spices, while most animals and especially insects hate it. In my Florida garden squirrels absolutely hate citrus tries, while trying to eat anything else. Such plants as oregano, mint, rosemary, thyme are never eaten by any insect.

  4. Galina L.
    Galina L. says:

    May be organic vegetables are the worse choice from the chemical warfare point of view, such vegetables generate more own toxins to discourage insects. It is especially noticeable in a notoriously insects-reach state as Florida. Once I had to throw away a cabbage soup I made out of organic cabbage head I had received as a gift, because the cabbage was still very bitter even after cooking. I am eating plants as indulgence foods, and consider it what it is – taste indulgences, expensive food toys, not a goldmine of vital nutrients, and I absolutely don't try to "eat my 5".

  5. wjones3044
    wjones3044 says:

    If I did not love my rats I would boil some cassava and feed one an ounce or two. Just kidding Larry, Moe, & Curly! (Not really…I really want to try this.)

    Interesting to note that rats don't like very many vegetables. They're really facultative carnivores. They tolerate nuts and some seeds–but by no means all seeds…birdseed kills them, as I found out when one got loose and devoured a bunch overnight.

    Anyway, spinach, broccoli, peppers–they'd have to be starving to eat those foods. What they really want are mealworms, raw hamburger, bacon. And they do like their peanut butter. The fattier the food, the better it seems. They know where it's at.

  6. Galina L.
    Galina L. says:

    I have a chance to observe another kind of rat-like animals – squirrels. They are happy to eat berries, pit fruits, tomatoes, acorns, less interested in figs, and absolutely hate citruses. Red peppers didn't interest them at all. When starved, they nibble on young shots of not fragrant tries, especially mulberry tree. They are absolutely crazy about peanut butter – they managed to brake a bird-feeder to get that thing out.

  7. Larcana
    Larcana says:

    Thanks for the article. I'm also, wondering about cruciferous veggies being so good for us. They are touted as such but give horrible gut issues. I found I can tolerate their bitterness with a lot of butter or cheese.

  8. Galina L.
    Galina L. says:

    I guess that usefulness of vegetables as food could be improved by proper cooking, it is almost the same situation as with grains which are more agreeable for a digestion after soaking and fermenting. For example, in old cooking traditions cabbage was always cooked till completely tender or fermented. I was raised during socialism, we had very limited choice of vegetables (onions, carrots, potatoes, winter reddish, fermented cucumbers, tomatoes and a cabbage) at a winter time, and most of the time it was a cabbage. Once i ate very lightly cooked broccoli(Michele Obama would approve) during my air travel, and a flatulence was unbelievable.
    I remember our cravings for a fresh young vegetables at the end of winter and an early spring.
    Very often humans have to figure out ways to stretch their meat, here come grains, and I guess the presence of vegetables in a mixed diet diminishes negative sides of eating grains. For me using vegetables allows having more fun with food. It is liberating to understand that you don't need to eat as much plants as you are told. Salads and vegetable stews are just pleasant foods to eat. Unless it is a problem for some.

  9. wellnesswish
    wellnesswish says:

    Hi Galina – "and a flatulence was unbelievable" on an aeroplane no less! Words for those of us challenged by vegetables to remember for ever 🙂 I also do far better on less vegetables. I found them very useful to soak up lots of meat fat/butter. Also noticed that the more fat on the veggies the less digestive distress. Life better with less veggies I think but cooking less exciting.

  10. Galina L.
    Galina L. says:

    Luckily the plane was empty at the tail end, and I could relocate myself there , or I din't know how I would survive that 10 hours flight. I cook broccoli for a broccoli soup on a skillet with a fat, salt and a little bit of soda first for 20 minutes. It tastes nutty and mild than, and no offence on my internal organs. It is a nice comfort soup for a winter time. I don't like how a bone broth tastes, and vegetables allow me to mask the taste.

  11. Galina L.
    Galina L. says:

    Nowadays a food which contains very little nutrition is recommended as a healthy one. Very lightly cooked or raw vegetables just create a bulk, and it is considered to be ideal.

  12. peterson
    peterson says:

    In any case, that shouldn't generally be the situation. Presently is the best time to assemble a strong establishment for appropriate nutrition by instructing and urging them to eat healthy sustenance for youngsters.See more

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