Adopting a low FODMAP diet relieves irritable bowel syndrome better than medicine

Two kinds of diet seem to work better than taking medication in addressing irritable bowel syndrome (IBS), a trial has found.

One diet was designed to be low in “FODMAPs”, a group of sugars and similar carbohydrates found in dairy, wheat and certain fruits and vegetables. The second was a less common approach used for IBS: an adapted low-carb diet that is high in fibre but low in all other kinds of carbohydrates, namely sugar and starch.

In a randomised trial, both diets led to better improvements in symptoms than standard treatment with medicines after four weeks.

IBS can cause a puzzling range of symptoms, including diarrhoea, constipation, bloating and abdominal pain, which can wax and wane over time. The root cause of the condition is unclear.

The usual advice is to avoid common triggers, such as caffeine, alcohol or spicy food. People may also take symptomatic treatments, such as laxatives for constipation or medication for diarrhoea.

If those measures don’t work, people may also try reducing food high in FODMAPs, which are thought to contribute to bloating and diarrhoea because they tend to go undigested until they reach the colon. This encourages water retention by the colon and produces gas as the molecules are consumed by bacteria, which contributes to bloating.

Sanna Nybacka at the University of Gothenburg in Sweden and her colleagues wanted to see how the usual low-FODMAP diet stacked up against the different approach of low-carbing while still eating plenty of fibre. In practice, this meant eating high-fat and high-protein food, such as meat and dairy products, while fibre sources included nuts, seeds, beans and vegetables, such as cabbage.

The team asked about 300 people with IBS to use one of three approaches: taking medicines as needed for their symptoms or adopting either of the two diets. For the dietary approaches, people were sent free grocery deliveries, as well as given detailed meal plans and recipes.

After a month, 76 per cent of those in the low-FODMAP group reported a significant reduction in their symptoms, compared with 71 per cent of those on the low-carb diets and 58 per cent in the medical treatment group.

The big surprise was that a low-carb, high-fibre diet, which didn’t exclude FODMAP-containing food, was about as effective as a low-FODMAP approach, says Nybacka. “We cannot provide any answers to why that is. It seems like modifying the carbohydrate contents and lowering the FODMAP intake might be beneficial.”

But Hazel Everitt at the University of Southampton in the UK says the trial would have been more useful if it had lasted longer. “The problem with many proposed IBS diets are that they are very difficult to maintain long term,” she says.

The participants were followed for up to six months, but for the last five months, those offered the medication approach initially were also given dietary advice.

Nybacka says one potential problem with the low-carb, high-fibre diet is that those in this group saw a small rise in their blood cholesterol levels. People should therefore seek their doctor’s advice before adopting this diet, she says.