Science Questions

Why are some parts of rhubarb poisonous?

When I was a lad I was told that rhubarb stems could be eaten but the leaves are poisonous. Why’s that? Paul Anderson

Helen - They contain something called oxalic acid. The reason it’s in the leaves is because it’s there to put predators (herbivores who come along and munch them) off. It’s not good for them and it’s not very good for us as well. You would have to eat an awful lot of it to actually kill yourself. The lethal dose: LD50 which is enough to kill off 50% of the rats that are given the dose of 375mg per kg of rat. That would equate in humans to around 5kg of leaves which anyone would believe is rather a lot. Yes. It’a problem. It acts through your kidneys. It’s a compound that actually interacts with metal ions and can form crystals and trigger kidney stones. That can be a problem. Symptoms include weakness, burning of the throat and mouth, difficulty breathing and if you’re really unlucky – a coma. Stear away from those rhubarb leaves I think is the answer.

Chris - What I want to know is who discovered that you could eat the bit in the middle but not the bit at each end.

Helen - So many questions on food. There’s the weirdest foods in the world that you’d never imagine. Someone, I think, tries anything.

November 2008