Eat kiwifruit for constipation, new guidelines say. But ditch the high-fibre diet

New guidelines on what to eat and drink if you have chronic (long-term) constipation have been making news in recent days.

Much of the media coverage of the British Dietetic Association’s guidelines has focused on advice to eat kiwifruit every day.

Meanwhile, other recommendations have not received so much attention. One, in particular, marks a shift in managing chronic constipation. The guidelines don’t advise a high-fibre diet.

Here’s what the guidelines say help (and don’t help) to relieve chronic constipation.

What did the guidelines look at?

Researchers examined 75 clinical trials to come up with recommendations for food, drink and supplements for chronic constipation in adults.

The quality of the clinical trials varied and so they had to come up with a consensus on the quality of the trial data.

Given that constipation means different things to different people, they used a very broad definition for constipation. This encompassed what patients perceived to be constipation as well as definitions of constipation used in clinical trials. Chronic constipation is generally when someone passes few, hard stools over a period of at least three months.

The researchers produced 59 recommendations. However, the researchers said most of the recommendations were based on poor-quality evidence.

Why kiwifruit? How many a day?

The researchers recommended eating two to three kiwifruit a day for at least four weeks to improve constipation. Whether it’s green kiwifruit or gold kiwifruit the evidence clearly shows they can help.

But how? There are several reasons.

Fibre in kiwifruit swells a lot when mixed with water, more so than apple fibre. This swelling helps make stools more bulky, easing their way through the gut.

Eating the whole fruit including the skin provides more fibre than just eating the flesh but eating the kiwifruit without the skin is perfectly fine.

Green kiwifruit contains an enzyme called actinidin that helps the body digest protein in the stomach and the small intestine. This may help with constipation by making food proteins softer and easier to pass through the gut.

Kiwifruit contain a type of crystal called raphides. These are believed to increase mucus production in the gut, lubricating it and helping passage of the stool.

Eating kiwifruit may also result in reduced species of methane producing bacteria, which have been linked to constipation.

Mineral water and magnesium

The researchers reported on the benefits of drinking mineral water. They suggested drinking 0.5–1.5 litres a day (roughly two to six cups) of mineral water for two to six weeks.

Why? Mineral water often contains magnesium, which acts as a laxative. Indeed, magnesium oxide is often used as a dietary supplement for chronic constipation.

The guidelines confirmed magnesium oxide can help soften the stool and increase stool frequency. The researchers recommended taking 0.5–1.5g a day for at least four weeks.

But this may not be appropriate for everyone. For instance people with kidney disease need to be careful. Magnesium supplements may also interact with other medications.

Read more: Should I take a magnesium supplement? Will it help me sleep or prevent muscle cramps?

Rye bread

The researchers cited studies showing rye bread relieves constipation more than white bread or common laxatives.

They recommended six to eight slices a day of rye bread for at least three weeks.

But this just isn’t realistic for a lot of people. And as rye contains gluten, this would not be appropriate for people with coeliac disease.

A high-fibre diet may not be needed after all

There was one key surprise in the guidelines.

The researchers said there was a lack of strong evidence for generic high-fibre diets for constipation, when people eat at least 25g of fibre a day.

Here’s the rationale. The researchers could only find one randomised controlled trial – the gold standard for testing interventions, such as a change in diet – where a high-fibre diet (25–30g/day) was compared with a low-fibre diet (15–20g/day).

This trial showed no benefit for the high-fibre diet in improving constipation. People on the low-fibre diet farted less and were less bloated than people on the high-fibre diet.

This does not mean fibre doesn’t help constipation. There is good evidence for supplementing your diet with more fibre to help chronic constipation.

But rather than focusing on a high-fibre diet for constipation, the guidelines instead recommend taking at least 10g a day of a fibre supplement, such as psyllium.

A high-fibre diet is usually a key part of national dietary guidelines. For example the Dietary Guidelines for Americans recommends some adults have a dietary fibre intake of at least 28g a day. There are certainly health benefits such as lowered cholesterol and blood sugar levels from eating a high-fibre diet.

But we now know it’s not needed to relieve chronic constipation.

What can we take away from the guidelines?

These guidelines provide more personalised, evidence-based dietary advice tailored to patient symptoms than previous guidelines.

Kiwifruit are considered a safe and effective treatment for chronic constipation. Mineral water, magnesium supplements and rye bread can help too.

But it would be worth discussing magnesium supplements with a health professional, especially if there are concerns about kidney disease or you take other medications.