Never eat an ugly fish
Casava Palaver
Curse of the lectins
No escape from aflatoxins
Never eat an ugly fish!
If you thought all fish was good for you, you might want to reconsider. Ever heard of fugu? It’s a traditional Japanese delicacy, a type of puffer fish (genus Takifugu), the only food the Japanese emperor is forbidden to indulge in. The taste of fugu is said to be quite bland, unless it’s been prepared in the “right” way, in which case the diner experiences a slight tingling sensation and subsequent numbness of the lips and tongue. The tingling is caused by tetrodotoxin (anhydrotetrodotoxin 4-epitetrodotoxin), a powerful nerve poison. The flesh of the fish is harmless – the poison is mainly stored in the liver, the reproductive organs, the intestines and the skin. One fish may contain enough tetrodotoxin to kill 30 people. Only licensed chefs are allowed to prepare and sell fugu to the public, and they train for about three years to learn how to avoid contaminating the edible parts of the fish with lethal amounts of poison. Still, accidents do happen, and there are an estimated 50-100 fatalities each year.
Death by tetrodotoxin poisoning is anything but a quick’n’easy way to exit, and there is no antidote. So, what would happen to you? The toxin disables your entire electrical signalling system by blocking your nerves’ sodium channels, inhibiting the propagation of action potentials. In other words, it shuts down your nervous system. First symptoms usually occur around 20 minutes after ingestion, but could take up to three hours to set in. The initial sensation of tingling and numbness spreads from your mouth over the rest of your face, working its way down your arms and legs. Headache, stomach pain, nausea and vomiting follow. Paralysis encroaches, you won’t be able to scream, never mind speak, and soon you will be unable to move. But don’t worry, you won’t miss a thing – you’ll remain fully conscious throughout. Breathing will become increasingly difficult, and once your respiratory system fails, you’ve pretty much had it. Not all fugu poisonings are fatal, of course, and if you make it through 24 hours, you will most likely recover completely. Occasionally stories surface in the Japanese press about fugu poisoning victims knocking from inside coffins minutes before their cremation.
As you’d expect, fugu is fairly expensive – sometimes over £100 for a full meal, although you can sample it as part of a less elaborate culinary affair for under £20. And to be fair, fugu poisoning is rare and mainly happens when untrained people catch and prepare the fish. So, next time you’ve in Japan, give it a try! Or maybe just have a burger instead.
Casava Palaver
Cassava, also called manioc, is a woody perennial shrub of the spurge family (Manihot esculenta), indigenous to tropical South America. Its fleshy, tapering roots have a high edible starch content of 30-35%, and crop yields can exceed 20 tons of roots per acre. These qualities make cassava a highly popular staple crop, and as many as 300 million people in the tropics and subtropics consume it daily. Cassava can be prepared in countless ways, e.g. boiled, baked, fried and made into flat breads. You may have eaten cassava yourself, it’s what tapioca pudding is made of, and health food shops sell bags of very tasty cassava chips.
The cassava products, which are imported into the UK, are made from sweet cassava. The poorer populations of tropical countries depend on bitter cassava for their sustenance. The bitter variety produces much higher yields than sweet cassava. There is one other crucial difference between the two: bitter cassava is laced with cyanide through and through (which is why it’s bitter). The cyanide occurs in the form of cyanogenic glucosides, mainly linamarin, and a tiny amount of lotaustralin (methyl linamarin). In the sweet variety, those cyanide compounds are mainly confined to the skin, which is easy to peel off. People who consume cassava as a staple have developed various ways of detoxifying the roots before consuming them. The most effective methods are grating and crushing, because the roots also contain the enzyme linamarase, which breaks down the linamarin and enables it to escape into the air as cyanide gas. Linamarase and linamarin are stored separately in the plant’s cells, so only by breaking down the cell structure can this process happen effectively.
Other methods are also used, such as boiling, sun drying and fermenting. The problem is that these aren’t always adequate. Some African regions, for example, are frequently afflicted by drought, which causes cassava to accumulate very high levels of cyanide. Grating and crushing are very labour intensive, and many cultures have not adopted this way of processing. A disease called konzo, prevalent in southern, eastern and central Africa, is thought to be a result of chronic cyanide poisoning caused by cassava consumption. Konzo causes sudden and irreversible paralysis of the legs, which mainly affects children and young women. TAN (tropical ataxic neuropathy), which can lead to blindness, deafness, and difficulty in walking, is found mainly in western Africa among older people, who have subsisted for a long time on a monotonous cassava diet. This is a case of cruel irony: the very food which many populations depend on to sustain life is also what debilitates and kills them – and what makes matters worse is that this unfortunate situation is entirely preventable.
Curse of the lectins
Less than half a dozen kidney beans (phaseolus vulgaris) can make you as sick as a parrot. Surprised? Well, you would be, seeing that you’ve probably had nearly as many chilli con carnes as you’ve had hot dinners with no ill effects … apart from maybe a bit of wind. But don’t be fooled – those innocent looking red beans harbour the potential for hours of torture. The evil force within them are lectins, also called phytohaemagglutinins, a type of protein found in many types of beans. Kidney beans have the highest concentration of lectins.
Why are lectins so terrible? For two main reasons: they bind to intestinal cells preventing nutrient absorption and, when they enter the blood stream, they also bind to red blood cells. This causes the red blood cells to clump together, a process referred to as “agglutination”, rendering them useless. Symptoms of “red kidney bean poisoning” occur 1-3 hours after consumption, entailing extreme nausea, severe vomiting, followed by diarrhoea and abdominal pain. Recovery is usually rapid, and sets in after 3-4 hours.
You’re probably still wondering why this has never happened to you. The answer is simple: lectins are inactivated during cooking. Tinned kidney beans are always cooked, and when buying them dried, they are soaked and boiled before eating. It takes only four to five raw kidney beans to trigger symptoms – and, paradoxically, undercooked beans are worse than raw beans. You should, for example, never use dried or raw beans in a slow cooker, which cooks foods at low temperatures over extended time periods. Heating kidney beans to only 80°C (i.e. below boiling point) can turn them five times more toxic. To be on the safe side, you should soak dried kidney beans in water for at least 5 hours, pour away the water, and then boil them for at least one hour in fresh water. Raw beans need to be boiled for a minimum of ten minutes. Even green beans, such as French or runner beans, contain a small amount of lectins and should not be eaten raw.
The good news is that there is some interesting research going on in trying to find medical applications for lectins. Two promising areas are HIV and cancer, for which the selective toxicity of lectins may be harnessed.