Is Rhubarb Poisonous Raw?

The part of the rhubarb plant usually eaten is the stalk. In the United States, the stalks are usually made into a pie. The leaves are technically edible, as well. It is variously reported that rhubarb contains poisonous compounds, or that you can only eat it cooked. In truth, you can eat the stalks raw, although the flavor is quite tart! Both the stalks and the leaves contain dangerous oxalic acid but only the leaves contain enough to be harmful.

During World War I, rhubarb leaves were erroneously recommended as a food source, causing many people to become ill and killing others.

During normal times, it is unlikely that anyone would consume enough of the leaves, which are extremely sour, to become poisoned, as it would require over ten pounds, or 5kg of the leaves to reach the toxic dose of oxalic acid for a 150lbs person.

The stalks also have a tart flavor, and some of this is due to oxalic acid, but the tartness is mostly due to the presence of malic acid. The leaves may also contain an additional toxin, perhaps an anthraquinone glycoside (senna glycoside), which has not been definitively identified.

Is Oxalic Acid Dangerous?

Oxalic acid does not deserve the killer reputation it is assigned on many web sources. We consume it every day as it occurs in many foods in small amounts.

Cacao, from which chocolate is made, contains one of the largest amounts of oxalic acid, at 500mg per 100 grams. Swiss chard has even more, with 700mg.

Spinach, strawberries, potatoes, many beans, almonds, walnuts, carrots, coffee, and various other foods all contain oxalic acid in varying, but usually small, amounts. Peanuts are particularly high, with 150mg per 100 grams.

You probably consume around 150mg of oxalic acid on an average day and right now, your blood plasma contains oxalic acid and oxalate salts. If you drink a lot of tea, that level goes up as tea contains around 50mg per cup.

However, a fatal dose is 1500mg. To reach this dose in one day would be almost impossible as you would become quite full, and feel sick, long before you could. Poisoning is not a problem; nutrition is.

Oxalic Acid in Nutrition

Oxalic acid is known as an anti-nutrient as it interferes with the absorption of many essential minerals including calcium, iron, and magnesium. Oxalic acid is the reason that many highly touted vegetables, like spinach, are not good sources of certain minerals, like iron, as the oxalic acid causes only around 5% of the iron content to be actually absorbed.

This affinity to metals is how oxalic acid kills, although, as stated, it rarely does. A critical dose of oxalic acid in the body lowers our calcium to such a low point that our bodies cannot continue functioning normally.

Non-lethal but habitual consumption of oxalic acid-containing foods can lead to the formation of calcium oxalate, which forms bladder and kidney stones. Not everyone is prone to this happening, however.

A varied diet that does not rely too heavily on one type of food, especially those high in oxalic acid, and plenty of fluids, is the primary preventative.

Despite all these dangers, the human body seems to be able to deal with quite large amounts of oxalic acid, and necessarily so. After all, it’s even an end-product in the body and vitamin C can be converted into oxalate, which is one reason you should avoid excess vitamin C supplementation.