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Relation
Eswaran SL, Chey WD, Han-Markey T, Ball S, Jackson K. A randomized controlled trial comparing the low-FODMAP diet with modified NICE guidelines in US adults with IBS-D.Am J Gastroenterol. 2016;111(12):1824-1832.
Objective
Comparison of nutritional counseling on low fermentable oligo-, di- and monosaccharides and polyols (FODMAP) with nutritional counseling on conventional irritable bowel syndrome (IBS) for patients with IBS with diarrhea (IBS-D).
Draft
In this randomized controlled trial, researchers used a modified version of the National Institute for Health and Care Excellence (NICE) guidelines for IBS nutritional advice as an active control. The participants and dietitians could not be blinded, but the rest of the study staff could. Participants were not told which diet was the true intervention diet. There was a 2-week run-in period and a 4-week intervention period.
Participant
Ninety-two participants (71% female) with IBS-D were randomized; 84 participants completed the study and were included in the primary analysis.
intervention
The low FODMAP diet was the intervention. The comparison diet used as an active control was the NICE recommended IBS diet modified by removing legumes and onions (mNICE).
Study parameters assessed
Food intake, IBS symptoms including abdominal pain and bloating, stool frequency, and stool consistency were assessed.
Primary outcome measures
The primary outcome was the proportion of participants who experienced “adequate relief.” This was defined as those patients who reported “adequate relief” of their IBS symptoms ≥50% of the time during the second half of the 1-month study.
Key insights
Fifty-two percent of participants who were recommended a low FODMAP diet reported “adequate relief” from their IBS-D symptoms, compared to 41% of participants who were given NICE IBS dietary recommendations. This did not reach statistical significance (P=0.31). Statistically significant benefits were observed in some secondary endpoints such as abdominal pain, bloating, and stool form and frequency.
Practice implications
Overall, this was a well-conducted study. Some points in favor of the study are adequate randomization, prospective registration and cleara prioriprimary outcomes, adequate active control and few dropouts (even if unbalanced).
My biggest concern from a clinical perspective is the difficulty patients have in following a low FODMAP diet.
As with any process, there are some concerns. Of course, the participants and the nutritionists were not dazzled. However, the study authors were careful to disguise which diet was the intervention diet, so placebo effects likely occurred in both groups and may have canceled each other out. The same cannot be said for nutritionists, so performance bias is still possible.1Meta-epidemiological research has shown us that we need to be most concerned about such biases in subjectively reported outcomes such as the primary outcome of “adequate response” of this study.2Therefore this is a problem; However, this cannot be avoided in nutritional intervention studies for IBS because they cannot be blinded and IBS results are necessarily subjective. The sponsors of the study were primarily academic centers and did not appear to have a direct mechanism to bias the outcome. However, one of the lead authors received funding from Nestlé, which currently markets heavily low-FODMAP foods.
This is actually the second randomized controlled trial comparing low FODMAP diets with conventional IBS dietary recommendations for IBS. The first study, conducted in Sweden and published in 2015, also found no statistically significant improvement in the primary outcome.3This study also used the NICE guidelines for IBS nutritional advice as a control diet. In contrast, this American study modified the NICE guidelines for its control group by removing language around avoiding high FODMAP foods such as onions and beans. This way, only the intervention group would avoid high FODMAP foods.
Results for the primary outcome in this study were negative, suggesting that avoiding high FODMAP foods may not have an effect beyond that seen with standard dietary recommendations for IBS. It is also possible that there is an effect above standard IBS dietary advice, but that it is a smaller effect than expected and this study was not powered to detect it (Type II error, also known as false negative). To clarify this, larger studies or meta-analyses of several smaller studies would be required.
While the primary endpoint did not reach statistical significance, there appears to be an improvement in some individual symptoms such as bloating, abdominal pain, stool shape and consistency. However, apparently these improvements were not enough to convince patients that they were receiving adequate symptomatic relief from their irritable bowel syndrome.
I believe this study was conducted as well as it could have been. I would have been happy with an effect size in the 10% range if it had been statistically significant. My biggest concern from a clinical perspective is the difficulty patients have in following a low FODMAP diet. If the authors actually found an effect in the 30% range, as they originally expected, it might seem reasonable to get a patient to follow such a challenging diet.