Deadly Dinners

Our mission at Halton Food is to encourage everyone to eat fresh, nutritious, organic fruits and vegetables that have been home grown or grown locally. That being said, it is important to realize that not everything grown in your garden is safe to eat. Not all parts of a vegetable are edible, and not all vegetables are safe to consume raw. We invited Master Gardener David Marshall to share with us a few common plants we need to be mindful of as we start to reap the bounty of our harvests this fall. 

David Marshall is a member of Oakville and Bronte Horticultural Societies, and has been a Master Gardener with the Halton Region group for almost thirty years. He has been gardening, with a few breaks, for over eighty years since he first helped his father in their big garden in war time England. He has been making compost in his Oakville garden for fifty years and has no plans to leave all that great soil behind in the foreseeable future. 

Deadly Dinners….

No, I am not talking about the Murder Mysteries which are sometimes staged at dinner parties, nor even the possible hazards of eating out in this COVID era. I mean the potential toxicity of some of the everyday fruits and vegetables which we eat. Be assured that you are unlikely to develop alarming symptoms if you prepare them correctly, but you never know! 

POTATOES: Potatoes are a member of the nightshade family contain solanine, which is normally broken down in the cooking process, but if the potatoes are subject to light for a long time green areas may form on the skin. These green areas contain excessive amounts of solanine, which must be cut off, otherwise gastrointestinal problems may result.  

RED KIDNEY BEANS: Red kidney beans should never be eaten raw or under cooked. They contain phytohaemagglutinin which causes severe nausea and vomiting, but which is destroyed with proper cooking. I recall a Dick Francis novel where an attempt was made to ruin the reputation of a restauranteur by inserting undercooked beans in a catered event.  

CORN: Corn can be hazardous if eaten regularly in large amounts. Traditional native American recipes call for the addition of slaked lime. Without it the niacin in corn cannot be absorbed and this can result in a severe niacin deficiency which causes a disease called pellagra. Back in the eighteenth century, large quantities of corn were imported into Spain from the New World and eaten in large quantities by impoverished people. Pellagra occurred and the symptoms were known as the four D’s: dermatitis, dementia, diarrhea, and death. In the first half of the twentieth century pellagra sickened three million Americans, and killed one hundred thousand.  

RHUBARB: Rhubarb stalks are safe to eat, but the leaves contain high levels of oxalic acid which can cause breathing difficulties and gastrointestinal problems. In 2017, a minister died after eating a dish made from rhubarb leaves. During the First World War food was scarce and his cook had found a recipe in the Times newspaper entitled “War Time Tips from the National Training School of Cookery,” (Don’t worry about your compost pile. Composting destroys the oxalic acid).  

ELDERBERRIES: Elderberries are popular in jams and pies (and wine), but raw elderberries contain low levels of cyanide. In 1983 a group of people attending a health retreat in California had to be air lifted to hospital with severe nausea after drinking fresh elderberry juice.  

CASHEWS: Cashews are members of the same family as poison ivy. The nut forms on the outside end of the fruit. Although the nuts are perfectly safe to eat, if the nut contacts any part of the shell during processing, they can cause a rash. For that reason, the shells are steamed open, which kills the toxin. In 1982 a Little League team sold bags of cashews which were contaminated with bits of unprocessed shell, and half of the people who bought them developed a rash and blisters similar to poison ivy.  

STONE FRUIT: Stone fruit such as apricots and peaches contain a substance called amygdalin in their pits, as do the seeds of apples and pears. This can release cyanide in the stomach, but I don’t suppose anyone knowingly eats the pits.  

GRASS PEA: Grass pea has been a dietary staple for centuries in India, Africa and the Far East and is an excellent source of protein. However, it contains a neurotoxin called, wait for it, beta-Noxalyl– diamine propionic acid, thankfully shortened to beta-ODAP. This can cause weakening of the legs and eventually paralysis from the waist down. To remove the toxin the peas must be soaked in water for a long time. Grass peas are one of the few food crops which can survive a severe drought. People are thus left with nothing else to eat and not enough water to soak the peas properly, and in times of famine many people succumb to the neurotoxin. Hippocrates wrote that people who “ate peas continuously became impotent in the legs”.  

Further readings: 

Green potatoes: 

Food Safety Authority of Ireland. 2015. Green Potatoes.         [Online]. Available: [7, Oct. 2020]. 

Raw red kidney beans: 

Meimann, Liz. 2013. Eating red kidney beans can be toxic. Iowa State University Extension and  Outreach. [Online]. Available:,are%20properly%20cooked%20by%20boiling. [7, Oct, 2020]. 


Bender, D.A. 2003. Pellagra. Encyclopedia of Food Sciences and Nutrition (Second Edition).  [Online]. Available: [7, Oct. 2020].  

Redzic, Sasa et al. 2020. Niacin Deficiency.[Online].  Available: [7, Oct. 2020].  


Oregon State University Extension Service. 2013. Are Rhubarb Leaves Toxic? Oregon State University.  [Online]. Available: [7, Oct. 2020].  


Berezow, Alex. 2019. Tincture of Elderberry: How a Professor Poisoned Herself with Cyanide. [Online]. Available: [7, Oct. 2020]. 

Centre for Disease Control. 1984. Poisoning From Elderberry Juice- California. [Online]. Available: [7, Oct. 2020]. 


Centre for Disease Control. 1983. Dermatitis Associated with Cashew Nut ConsumptionPennsylvania. [Online]. Available: [7, Oct. 2020]. 

Stone Fruit: 

Canadian Food Inspection Agency. 2019. Natural Toxins in Fresh Fruit and Vegetables. Government of Canada. [Online]. Available: [7, Oct. 2020]. 

Grass Pea: 

The Curious Case of the Grasspea. 2013. Crop Wild Cousins. [Online]. Available:,-Now%2C%20before%20we&text=Eaten%20in%20small%20quantities%2C%20grasspea,a%20potent%20neurotoxin%20called%20ODAP. [7, Oct. 2020].  



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