Inside Our Food

Toxic Foods | 5 Delicious but Deadly Foods

We all know to steer clear of the mysterious looking mushrooms growing in the wild. What many might not realise is that a number of supermarket staples, commonly consumed at home, are also potentially dangerous foods. Here are 5 potentially toxic foods you could be eating ‘wrong’.

The wrong part of rhubarb

For many common fruits and vegetables, the leaves are not only harmless but often highly nutritious. For certain plants, however, consumption of these extraneous elements can be harmful. Rhubarb, a vegetable that is more commonly treated as though it were a fruit, falls into this second category. Although the stalks are a staple for any crumble or cobbler, their leaves contain high concentrations of an organic compound called oxalic acid. Whilst it is thought that the compound is produced by a number of plants as a means of protection from pathogens, it is toxic not only to insects but to humans as well.1,2

Oxalic acid has the capacity to bind with calcium, forming an insoluble complex which can both block the urinary tract and form kidney stones, whilst also reducing the availability of calcium across the rest of the body, impeding a number of essential processes including neural transmission, blood clotting and bone formation. Although studies indicate that it would take around 22g of oxalic acid – between 1.5 and 5kg of leaves - to kill the average human, symptoms can be seen after ingestion of as little as 10g of fresh leaves.1,2,3

Green potatoes

You may have noticed that when left on the vegetable rack for just one week too long, potatoes begin to develop a green hue, and may even begin to sprout. Whilst the green itself is just perfectly harmless chlorophyll, it is indicative of the potato becoming ‘over-ripe’, with new potato growth beginning to take place. At this point, in addition to increased concentrations of chlorophyll, the potato is now also producing a number of significantly more toxic compounds known as glycoalkaloids - consumption of which can lead to a whole host of gastrointestinal and neurological complications. Whilst you will likely only see this in an ‘older’ potato - supermarkets and greengrocers would not stock potatoes still containing these compounds - it is not actually the aged potato, but rather this new growth which is the toxic element.4,5,6

Unfortunately, conventional cooking methods do not sufficiently deplete the levels of glycoalkaloids to make consumption safe; they are not water soluble, so do not leach into water if boiled, and they only experience significant levels of degradation at temperatures greater than 170°C. Whilst these compounds are highly concentrated in the skin and stems, the growth of the stalks allows for diffusion from the sprouts into the white flesh of the tuber itself. So, whilst peeling the potato will remove much of the fibre and nutrients, it won’t completely remove the risk. Although no maximum limit has been identified in glycoalkaloid consumption, it is recommended that if, once cooked, the flesh still tastes bitter, concentrations are likely unsafe, and your best bet is to pop not just the peel, but the whole thing in the bin.5,7

Raw beans

Thanks to the presence of two carbohydrate proteins known as PHA, consumption of raw or undercooked kidney beans can lead to widespread ill-health, including reduced food intake, stunted growth, and even death. Not only is PHA highly toxic, but it is also resistant to degradation by both digestive enzymes and gut-bacteria, meaning that, when consumed, it can pass through the consumer’s digestive tract functionally in-tact.8,9

Once in the gut, they bind with intestinal cell membranes and initiate a cascade of events which drastically alter the function of the digestive tract. Beyond the intestinal system, these compounds can also impact a wide array of organs including the pancreas, liver and thymus. The good news is that, although resistant to degradation in the gut, PHA is relatively sensitive to high temperatures, meaning that just 10 minutes of boiling should render your beans not only harmless, but highly nutritious. Alternatively, the canned typically come pre-cooked; less hassle and less worry!8,9,10

Cherry, Apricot & Peach Seeds

Whilst you may have been raised to eat everything on your plate, doing so would not be recommended when the food belongs to the genus Prunus. This includes the stones (aka: seeds) in stone fruits like apricots, peaches and cherries, which contain a substance called amygdalin. 

Once in the human body, amygdalin can be converted into cyanide which has the capacity to act on nearly every cell in the body, depriving it of oxygen. Cyanide is infamous for a reason; only very low concentrations are required to initiate severe symptoms including loss of consciousness, seizures and death. Whilst an apricot stone would likely need crushed prior to consumption in order for significant levels of toxin to be released, cherry stones, due to their smaller size, are more readily broken down in the gut, meaning that swallowing just a few stones could lead to some surprisingly unpleasant symptoms.11,12

Brazil nuts (& other selenium-rich foods)

Whilst the aforementioned killers provide no benefit to the consumer, there are a few naturally occurring components which are responsible both for a foods’ toxic tendencies as well as much of its nutritional value. Selenium, an immune-boosting, hormone-impacting essential mineral, that is involved in various biological functions, is one such compound.14

Selenium cannot be produced by the body, and thus it must be obtained either through diet or supplementation. Although present in a number of different foods including tuna and halibut, as well as beef, eggs and even certain breads, the highest dietary source–by quite some magnitude– is the Brazil nut. In order to reach the daily recommended intake of 55mcg, you would need to consume just under 3g, which equates to less than one average sized Brazil nut.14,15

Learn about the cost of Brazil nut production.

However, whilst selenium deficiency has been implicated in a number of severe conditions including cardiovascular disease, cognitive decline and infertility, the detrimental effects of excessive consumption are equally as widespread and damaging. Whilst in low doses it acts as an antioxidant, in just slightly higher concentrations it can act as a pro-oxidant, reaping its effects across the body. Whilst early signs of toxicity include diarrhea, bad breath, brittle nails and irritability, extremely high intake can cause difficulty breathing, kidney failure and heart attacks. Making matters worse, the upper limit is worryingly close to that of the recommended daily intake; at just 400mcg per day. Regularly eat 4 or more average sized Brazil nuts per day, and you might just start to feel the effects.13,14,15,16,17,18

These are just a few examples of common foods that can also be potentially toxic foods. Let us know which of your favourite foods have a surprisingly deadly side!

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  2. Food Safety Authority of Ireland (2015). “Green Potatoes”. Accessed 22 May 2020.
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  10. Mekonnen (2018). “Poison.org: I Swallowed A Cherry Pit! Are Stone Fruit Pits Poisonous?”. Accessed 25 May 2020.
  11. Shreenath; Dooley (2020). “Selenium Deficiency”. Accessed 23 May 2020.
  12. National Institutes of Health: Office of Dietary Supplements (2020). “Selenium. Fact Sheet for Health Proffessionals”. Accessed 23 May 2020
  13. MacFarquhar; Broussard; Melstrom; Hutchinson; Wolkin; Martin; Burk; Dunn; Green; Hammond; Schaffner; Jones (2011). “Acute Selenium Toxicity Associated with a Dietary Supplement”. Accessed 25 May 2020
  14. National Research Council (US) Subcommittee on Selenium (1981). “Selenium in Nutrition”. Accessed 25 May 2020.
  15. Rakel (2008). “Chapter 22 – Integrative Medicine” in Clinical Men’s Health. Accessed 25 May 2020.
  16. National Institute of Health, Office of Dietary Supplements (2019). “Selenium. Fact Sheet for Consumers”. Accessed 20 June 2020.
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