From April until the end of June, supermarkets everywhere will be stocking rhubarb in their produce section. Due to its sweet yet sour taste, it is ideal for compotes, jams and cakes. However, rhubarb also contains an extremely high amount of oxalic acid, a compound that is unhealthy in high amounts and which can cause kidney stones. In this article we look at just how high the oxalate content of rhubarb is and how it can be reduced through proper preparation.

What makes the oxalic acid in rhubarb so dangerous?

Oxalic acid is often referred to as an antinutrient because it hampers the body’s absorption of important minerals, such as calcium, magnesium and iron. In the acidic environment of the stomach oxalic acid binds with these minerals to form insoluble salts. If a meal contains significantly more oxalic acid than calcium, the body cannot make use of these minerals and may even be actively deprived of calcium (below you will find tips on how to counteract this effect). Oxalic acid and its salts – the oxalates – can be found in almost every plant-based food, and usually in safe amounts. However, the concentration in rhubarb is exceptionally high (see table 1).

Food	Oxalate content per 100 g
Rhubarb	1235 mg
Cashew nuts (roasted)	227.9 mg
Carrot	26.5 mg
Apple	3.5 mg

▲Table 1: Oxalate content of various assorted foods [Source: OxiPur].

How can we reduce oxalate levels when eating rhubarb?

Rhubarb’s oxalate content can be greatly reduced using various preparation methods. These include peeling the stalks, since the greatest concentration of oxalates is in the skin. All green leaf parts should be removed, since these are also abundant with oxalic acid. Finally, it’s recommended to boil rhubarb in plenty of water before discarding the water; this can remove a significant portion of the water-soluble oxalates. Rhubarb remains a very high oxalic acid food, though, so even following all these steps will not remove the oxalates entirely.

It should also be noted that the above measures cannot be applied in some of the most popular uses of rhubarb. When making a compote, for example, rhubarb is boiled in a small amount of amount of water, which retains the full oxalate content. Cakes also use finely chopped rhubarb, which will also have a certain amount. It’s a safe bet to assume that if you haven’t prepared a rhubarb dish yourself, it is likely to contain the highest possible quantity of oxalates.

Conclusion: who is at risk with oxalic acid?

For healthy individuals, occasionally eating foods rich in oxalic acid is not an initial cause for concern, but the potential consequences should not be underestimated. Kidney stones are an extremely painful affliction that can often be traced to bad nutrition over several years. It is well documented that excessive consumption of foods rich in oxalic acid – nuts or chocolate, for example – will cause problems, even for otherwise healthy people.

For illnesses such as recurring kidney stones, kidney disease, inflammatory bowel diseases or frequent diarrhea, you should closely monitor your oxalate content. You can refer to our OxiPur app for a quick overview of this. The crucial factor to watch out for is the content of soluble oxalates, because, unlike insoluble oxalates, these are efficiently absorbed and accumulate in the body (see figure 1).

▲Figure 1: Display of ingredients in the OxiPur app.

Consuming calcium can significantly reduce the harmful effects of oxalic acid because if there is enough calcium around it binds to the acid and renders it harmless. A neat trick, therefore, is to include, when necessary, calcium-rich foods in your diet, and especially with rhubarb. Eating a portion of whipped cream or drinking a glass of milk is a great way to combat the oxalates you are consuming in rhubarb. However, if you have already developed kidney problems or even have kidney stones, it is best to avoid rhubarb altogether.




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Photo by Julia Topp on Unsplash

Tags:Oxalate Oxalic acid Kidney stones