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, Dr. 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 able to collect stool samples from only 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, Fla., 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 this news organization. “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 Dr. Lacy.
The study was funded by Schaer. One of the study authors has reported receiving an educational grant from Schaer. Dr. Lacy has reported being on scientific advisory boards for Ironwood, Salix, and Allakos.
A version of this article first appeared on Medscape.com.