Three Popular IBS Diets Found Equivalent

Laird Harrison

March 10, 2022

Three widely followed diets for nonconstipated irritable bowel syndrome (IBS) produce similar results, but traditional dietary advice (TDA) is easier to follow, researchers say.

"We recommend TDA as the first-choice dietary option due to its widespread availability and patient friendliness," Anupam Rej, MBChB, from Teaching Hospitals NHS Foundation Trust in Sheffield, United Kingdom, and colleagues write.

According to their study, about half the people following each of three diets — TDA; gluten-free; and low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) — reported at least a 50% reduction in their symptoms.

They noted, however, that the low-FODMAP diet produced the most improvement in depression and dysphoria.

The study was published online in Clinical Gastroenterology and Hepatology.

What the Dietary Options Entailed

The three diets have different origins and methodologies, but all are designed to reduce the abdominal pain, bloating, and altered bowel habits that characterize IBS.

TDA is based on recommendations of the UK National Institute for Health and Care Excellence and the British Dietetic Association. It includes "sensible eating patterns," such as regular meals, never having too much or too little, and sufficient hydration. It calls for a reduction in alcoholic, caffeinated, and "fizzy" drinks; spicy, fatty, and processed foods; fresh fruit (a maximum of three per day); and fiber and other gas-producing foods, such as beans, bread, and sweeteners. It also asks people to address any perceived food intolerance, such as dairy.

In North America, the low-FODMAP diet is prescribed as first-line therapy, and the American College of Gastroenterology has given it a conditional recommendation.

FODMAPs are short-chain fermentable carbohydrates found in many fruits, vegetables, dairy products, artificial sweeteners, and wheat. They increase small intestinal water volume and colonic gas production that can induce gastrointestinal symptoms in people with visceral hypersensitivity.

People following the low-FODMAP diet start by eliminating all FODMAPs for 4 to 6 weeks, then gradually reintroduce them to determine which are most likely to trigger symptoms.

A gluten-free diet, inspired by what is prescribed to treat celiac disease, has gained popularity in recent years. Although researchers debate the mechanism by which this diet improves symptoms, one leading theory is a reduction in fructans that accompany gluten in foods such as bread.

A Rare Head-to-Head Comparison Trial

The low-FODMAP diet has proved itself in more clinical trials than the other two approaches, but few, if any, trials have compared them head-to-head in a pragmatic randomized trial, Rej and colleagues found after reviewing the literature.

They set about filling this gap by recruiting 114 people with IBS and randomly assigning each of them to one of the diets. Ninety-nine people finished the trial, with 33 following each of the diets. People with IBS-constipation were excluded.

Participants were a mean age of 37 years. Seventy-one percent were female, and 88% were White. Their mean IBS symptom severity score was 301, with 9% rating their symptoms as mild, 47% as moderate, and 45% as severe.

The proportion who reported at least a 50% reduction in their symptoms was 58% for the gluten-free diet, 55% for the low-FODMAP diet, and 42% for the TDA. The differences in these proportions were not significant (P = .43).

The diets worked about as well regardless of whether the patients had IBS with diarrhea or IBS with mixed diarrhea and constipation.

More of the people on the low-FODMAP diet reported significant improvement in their depression and dysphoria than people on the other two diets.

Changes in anxiety, somatization, and other aspects of IBS quality of life didn't differ significantly with diet.

Where the Diets Differ: Cost and Ease

Fewer people following the TDA rated it as expensive, difficult, or socially awkward compared with the people following the other two diets.

More of those following the TDA and gluten-free diet found them easy to incorporate into their lives than those following the low-FODMAP diet. About two thirds of the people in each of these groups said they would consider continuing their diets after the end of the study.

The proportion of people consuming the recommended dietary reference values for macronutrients did not change with any of the diets. However, those in the TDA group reduced their intake of potassium and iron. In the other groups, the researchers noted a reduction in thiamine and magnesium.

Because of COVID-19 restrictions, the researchers were only able to collect stool samples from half of participants. What they did collect showed no difference among the groups in dysbiosis index or functional bacterial profiles.

Baseline factors such as age, gender, IBS subtype, dysbiosis index, somatization, and mood, did not predict response to the three diets.

Participants improved as much whether they received dietary instructions face-to-face or through a live virtual consultation.

Applications and Limitations

At least one previous study showed that the low-FODMAP diet produced better results than the standard diets patients had been following, said Brian E. Lacy, MD, PhD, a professor of medicine at the Mayo Clinic in Jacksonville, Florida, who was not involved in the current study.

He agreed with the study's conclusion that the TDA could be a good place for people with IBS to start.

"Based on their research, and the findings that patients thought the diet was less expensive, easier to follow, and easier to shop for, this is a reasonable approach," he told Medscape Medical News. "However, if there's no benefit with the traditional diet, then moving on to the more rigorous low-FODMAP diet makes sense to me."

Study limitations include a short duration, lack of information about how patients can add foods back into their diet (particularly with the low-FODMAP diet), and insufficient sample size and lack of a placebo group contributing to an inability to detect all clinically significant differences among the diets, he said.

"Although this study is not definitive and doesn't answer all key questions about which diet is best and how each performs in the long run, it does provide important information for patients and providers," said Lacy.

The study was funded by Schaer. One of the study authors has reported receiving an educational grant from Schaer. Lacy has reported being on scientific advisory boards for Ironwood, Salix, and Allakos.

Clin Gastroenterol Hepatol. Published online February 28, 2022. Full text

Laird Harrison writes about science, health, and culture. His work has appeared in national magazines, in newspapers, on public radio, and on websites. He is at work on a novel about alternate realities in physics. Harrison teaches writing at the Writers Grotto. Visit him at or follow him on Twitter: @LairdH.

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