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In people with irritable bowel syndrome, very-low-quality evidence suggests low FODMAP diets improve symptoms. There isn’t enough evidence to draw conclusions about gluten-free diets.

Dionne J, Ford AC, Yuan Y, et al. A Systematic Review and Meta-Analysis Evaluating the Efficacy of a Gluten-Free Diet and a Low FODMAPs Diet in Treating Symptoms of Irritable Bowel Syndrome. Am J Gastroenterol. 2018 Jul 26. [Epub ahead of print].

Review question

In people with irritable bowel syndrome (IBS), do diets without gluten or low on fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) improve symptoms?

Background

IBS is a common disorder. It affects the large intestine, but does not harm it. We don’t have a specific test to diagnose IBS, and we don’t know exactly what causes it. People with IBS have symptoms such as constipation, diarrhea, stomach pain or cramps, bloating, and gas. IBS symptoms may be treated with drugs, changes in diet, probiotics, or stress-management strategies. This review looks at whether changing your diet can improve IBS symptoms.

A low FODMAP diet means that you remove specific foods from your diet that are poorly absorbed in the bowel (e.g., garlic, onions, many types of beans–a full list is easily found on the Internet). A gluten-free diet means that you remove foods that contain a protein found in wheat (e.g., cereals, pasta, breads).

How the review was done

The researchers did a systematic review of studies available up to November 2017. They found 9 randomized controlled trials that included 508 people.

The key features of the studies were:

• people were at least 18 years of age and were diagnosed with IBS;
• 2 trials evaluated gluten-free diets (GFDs), and 7 evaluated low FODMAP diets;
• GFD and low FODMAP diets were compared with placebo, usual diets, diets including gluten, or higher FODMAP diets; and
• people used the diet for 3 to 9 weeks.

What the researchers found

• Compared with diets including gluten, GFDs improved IBS symptoms at 6 weeks in 1 trial of 72 people but did not improve symptoms at 6 weeks in another trial of 39 people.
• Low FODMAP diets improved IBS symptoms overall at 3 to 9 weeks compared with other diets, high FODMAP diets, or placebo.

The quality of the evidence was considered to be very low, which means that new studies might show different results.

Conclusions

In people with irritable bowel syndrome, there is very-low-quality evidence that low FODMAP diets improve symptoms. We don’t have enough evidence about gluten-free diets to draw any conclusions.

Gluten-free diet (GFD) or low FODMAP diet vs control diet* for irritable bowel syndrome (IBS)

FODMAP = fermentable oligosaccharides, disaccharides, monosaccharides, and polyols.

*Placebo, usual diets, diets including gluten, or higher FODMAP diets.

†The proportion of patients with continuing symptoms in the GFD and low FODMAP diet groups were weighted. This means it may be a little different than you would expect if you just divided the number of people who had ongoing symptoms with the number of people who used the diet.

‡Although the rates for the 2 groups look a little different, the differences were not statistically significant. This means that the differences could simply be due to chance rather than due to different diets.