Study: Do low-Fodmap diets work at IBS-D?
Study: Do low-Fodmap diets work at IBS-D?
reference
ESWARAN SL, Chey WD, Han-Markey T, Ball S, Jackson K. A randomized controlled study for comparing the low-Fodmap diet with modified NYE guidelines in adults in the USA with IBS-D. Am J Gastroenterol . 2016; 111 (12): 1824-1832.
objective
Comparison of nutritional advice to low fermentable oligo, di- and monosaccharides and polyols (Fodmap) with nutritional advice on conventional irritable bowel syndrome (IBS) for patients with IBS with diarrhea (IBS-D).
draft
In this randomized controlled study, the researchers used a modified version of the guidelines of the National Institute for Health and Care Excellence (Nice) for IBS nutritional advice as active control. The participants and nutritionists could not be blinded, but the rest of the study staff. The participants were not told which diet was the true intervention diet. There was a 2-week inlet phase and a 4-week intervention phase.
participant
Ninety-two participants (71 % female) with IBS-D were randomized; 84 participants ended the study and were included in the primary analysis.
Intervention
The Fodmap-poor diet was the intervention. The comparison diet serving as active control was the IBS diet recommended by Nice, modified by removing legumes and onions (mnice).
study parameters evaluated
food intake, IBS symptoms including abdominal pain and flatulence, frequency of chairs and stool consistency were assessed.
primary result dimensions
The primary result was the proportion of participants who experienced an “appropriate relief”. This was defined as the patients who reported "adequate relief" of their IBS symptoms in ≥ 50 % of cases during the second half of the 1-month study.
important knowledge
fifty percent of the participants who were recommended to have a low-fodmap diet, reported of an "appropriate relief" of their IBS D symptoms compared to 41 % of the participants to whom Nice IBS diet recommendations were given. This did not achieve statistical significance ( p = 0.31). Statistically significant advantages were observed in some secondary endpoints such as abdominal pain, flatulence as well as stool shape and fraud.
practice implications
This was a well -carried out study overall. Some points that speak for the study are an appropriate randomization, prospective registration and a clear a priori primary results, adequate active control and few dropouts (even if they are unbalanced).
My greatest concern from a clinical point of view affects the patients' difficulties to comply with a low-Fodmap diet.
As with every process, there are also some concerns. Of course, the participants and the nutritionists could not be blinded. However, the authors of the study made sure to disguise which diet was the intervention diet, so that placebo effects probably appeared in both groups and possibly eliminated each other. The same does not apply to nutritionists, so that performance distortions are still possible. 1 Meta epidemiological research has shown us that we have to worry about such distortions in subjectively reported results such as the primary result of "adequate response". However, this cannot be avoided in nutritional intervention studies for IBS, since they cannot be blinded and the IBS results are necessarily subjective. The sponsors of the study were mainly academic centers and seemed to have no direct mechanism to distort the result. However, one of the leading authors received financial resources from Nestlé, which is currently marketing strongly Fodmap-poor food.
This is actually the second randomized, controlled study that compares low-Fodmap diets with conventional IBS nutrition recommendations for IBS. The first study carried out in Sweden and published in 2015 did not show any statistically significant improvement in the primary result. 3 In this study, the Nice guidelines for IBS dietary advice were also used as a control diet. In contrast, this American study modified the Nice guidelines for its control group by removing the language for avoiding food with a high fodmap content such as onions and beans. In this way, only the intervention group would avoid food with a high fodmap content.
The results for the primary result in this study were negative, which indicates that avoidance of food with a high fodmap content may have no effect that goes beyond those that are observed for standard nutrition recommendations for IBS. It is also possible that there is an effect that lies above the standard RDS nutritional advice, but that it is a lower effect than expected and this study was not designed to recognize it (type II error, also known as false-negative). To clarify this, larger studies or meta -analyzes of several smaller studies would be required.
While the primary endpoint did not achieve statistical significance, it seems to be improving some individual symptoms such as flatulence, abdominal pain, stool form and consistency. Apparently, however, these improvements were not sufficient to convince the patients that they received adequate symptomatic relief from their irritable bowel syndrome.
I believe that this study was carried out as well as it could have been. I would have been satisfied with an effect size in the range of 10 % if it had been statistically significant. From a clinical point of view, my greatest concern affects the difficulties of the patients to comply with a low-Fodmap diet. If the authors actually found an effect in the range of 30 %, as they originally expected, it could seem sensible to make a patient to carry out such a challenging diet.
- Higgins JPT, Green S, ed. Cochrane manual for systematic reviews of interventions version 5.1.0 [updated March 2011]. The Cochrane collaboration, 2011.
- Wood L, Egger M, Gluud LL, Schulz KF, June P, Altman DG, et al. Empirical detection of distortions in estimates of the treatment effect in controlled studies with different interventions and results: meta-epidemiological study. bmj . 2008; 336: 601.
- Böhn L, Störsrud S, Liljebo T, et al. A low-fodmap diet reduces the symptoms of irritable bowel syndrome and traditional nutritional advice: a randomized controlled study. gastroenterology . 2015; 149 (6): 1399-1407.