Two types of diets are more effective at treating irritable bowel syndrome (IBS) than drugs, a trial has found.

One diet was designed to be low in FODMAPs, a group of carbohydrates similar to sugars found in dairy products, wheat, and certain fruits and vegetables. The second, less common approach used for IBS is an adaptation of a low-carbohydrate diet that is high in fiber and low in other types of carbohydrates, such as sugar and starch.

In a randomized trial, both diets showed better symptom improvement than standard drug treatment after four weeks.

IBS can cause mysterious symptoms such as diarrhea, constipation, bloating, and abdominal pain that increase or decrease over time. The underlying cause of this condition is unknown.

The usual advice is to avoid common triggers such as caffeine, alcohol and spicy foods. Symptomatic treatments such as laxatives for constipation and drug therapy for diarrhea may be given.

If these measures don’t work, you may want to consider cutting back on foods high in FODMAPs. FODMAPs tend not to be digested until they reach the colon, which is why they are thought to cause bloating and diarrhea. This encourages the colon to retain water, and when the molecules are consumed by bacteria, gas is produced and causes bloating.

Sanna Niebacka Researchers from the University of Gothenburg in Sweden wanted to find out how a regular low-FODMAP diet compared to an alternative approach: high in fiber but low in carbohydrates. In practice, this means eating high-fat, high-protein foods such as meat and dairy products, and sources of fiber include nuts, seeds, beans, and vegetables such as cabbage.

The research team asked around 300 people with IBS to use one of three approaches depending on their symptoms: take medication or adopt one of two diets. The diet provided people with free grocery delivery, as well as detailed meal plans and recipes.

After one month, 76% of the low-FODMAP group reported a significant reduction in symptoms, compared with 71% of the low-carbohydrate diet group and 58% of the drug treatment group.

The big surprise was that a low-carbohydrate, high-fiber diet that didn’t exclude FODMAP-containing foods was about as effective as a low-FODMAP approach, Nybacka says. “We can’t answer any questions as to why. It appears that altering carbohydrate content and reducing FODMAP intake may be beneficial.”

but hazel everitt Researchers at the University of Southampton in the UK say the trial would have been more informative if it had lasted longer. “The problem with many of the IBS diets that have been proposed is that they are very difficult to stick to long-term,” she says.

Participants were followed for up to six months, but during the last five months participants who were initially offered drug treatment were also given dietary advice.

Niebacka says one potential problem with the low-carbohydrate, high-fiber diet is that this group of people had slightly elevated blood cholesterol levels. Therefore, you should seek your doctor’s advice before adopting this diet, she says.