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The beneficial laxative effect of rhubarb and kiwifruit

People eat rhubarb and kiwifruit to help stay regular, but there's more to it than just fibre.

Spring heralds the arrival of new rhubarb shoots in many gardens. Although this vegetable is traditionally served as a stewed dessert in New Zealand, rhubarb is one of the most ancient and important herbs in Chinese medicine.

Rhubarb (Rheum rhabarbarum) has been eaten as a food only relatively recently. British nurseryman Joseph Myatt is thought to have been the first to cook rhubarb with sugar, in the early 18th century.

The leaves of the rhubarb plant shouldn’t be eaten, as they contain poisonous substances such as oxalic acid. In traditional Chinese medicine, the roots of the rhubarb plant are prized for their laxative effect and it has been a treatment for constipation for thousands of years.

Those who eat the stewed fleshy stalks, or petioles, of rhubarb may also have noticed something of a laxative effect, too. It provides a good helping of fibre, with 2.4g per 100g of stewed rhubarb, contributing to the recommended daily intake of 25g for women and 30g for men.

But it is not rhubarb’s dietary fibre that is credited with promoting bowel movements. Instead, it’s a combination of compounds known as anthraquinones that are thought to be responsible. The compounds are metabolised by gut bacteria, resulting in increased bowel movements and more water being retained in the colon, leading to faster, looser movements.

A 2017 study by Japanese doctors found that among six critically ill patients who had suffered from constipation for an average of 5.8 days, a dose of powdered rhubarb produced a much-needed bowel movement within 1.8 days.

However, you’re probably not going to be prescribed a rhubarb-root supplement for constipation any time soon. That’s because, during research into its laxative effect in animals, Chinese researchers found that some of its compounds can be toxic to the kidneys and that long-term use can produce adverse effects.

Nevertheless, the rhubarb stalk is full of nutritious goodies. Along with the fibre, a 100g serving of stewed rhubarb also provides 8mg of vitamin C, anthocyanin compounds and antioxidant effects.

To aid digestion and remain regular, green kiwifruit is also a good option. In addition to the helpful 3g of fibre per 100g, and 85mg of vitamin C, it also contains actinidin – a natural enzyme that breaks down a range of food proteins faster than our own digestive enzymes.

Kiwifruit fibre also has a mixture of insoluble and soluble fibres that help to create a larger, softer stool that moves more quickly through the gut.

Clinical trials have found that green kiwifruit significantly improves digestive health, increasing frequency and ease of bowel movements in healthy adults and those with constipation, including adults who have the condition as a result of irritable bowel syndrome.

It’s amazing how natural wholefoods can benefit our gut health, and all while tasting delicious, too.

This article was first published in the September 14, 2019 issue of the New Zealand Listener.