IBS: is it possible to anticipate the response to a low-FODMAP diet?
Irritable bowel syndrome (IBS) is a true public health issue for which available treatments are very limited. Low-FODMAP diet is one of the key components of the treatment. This is why, a team of Norwegian researchers tried to determine whether the analysis of the intestinal microbiota could be used to predict its efficacy.
Because of the involvement of the enteric nervous system, hormones and microbiota, the irritable bowel syndrome is a complex disorder. As part of its treatment, national gastroenterological guidelines have included for several years a FODMAP-restricted diet which requires the patient' complete adherence to treatment and produces variable results depending on the individual. This study offers the possibility, in the medium term, to anticipate the clinical response to this therapeutic approach.
Different bacterial profiles
For a period of four weeks, patients had to follow a FODMAP-restricted diet. Clinical response was defined based on the IBS symptom severity scores (IBS-SSS) which takes into account abdominal pain, bloating, transit disorders and global impact of the disease. Positive response to diet (responders) was defined as ≥ 50% decrease in IBS-SSS. Fecal microbiota was also analyzed by a method assessing 54 bacterial markers (based on 16S rRNA sequencing) targeting more than 300 bacteria. The comparison of bacterial profiles revealed a significant difference between both patient groups: 29 classified as non-responders while 32 obtained a positive response to diet. Responders had significantly higher levels of Bacteroides fragilis, Acinetobacter, Ruminiclostridium, Streptococcus, and Eubacterium. On the contrary, non-responders had higher levels of Clostridia/Negativicutes/Bacilli, Actinomycetales, Anaerotruncus, Clostridiales, and Shigella/Escherichia. Even though looking for a potential dysbiosis was not the objective of the study, profiles more likely to respond to the diet were identified based on the statistical analysis resulting from this difference in bacterial markers.
Ten of the 54 bacterial markers differed significantly between responders and non-responders. This led the authors to create a response index (RI) (ranging from 0 to 10). This index showed a significant correlation between high scores and likelihood to obtain a positive response to the diet. Patients with an RI over 3 were 5 times more likely to respond. Although these results are not clinically applicable yet, they may pave the way for a potential tool in the future. This study also helped improve the understanding of IBS pathophysiology. It provides evidence regarding potential FODMAP-dependent bacteria present in certain patients for whom an appropriate diet could limit the inflammatory symptoms associated with the disease. According to the authors, the use of prognostic biomarkers could soon be part of the decision algorithm to treat irritable bowel syndrome.
Valeur, J., Småstuen, M. C., Knudsen, T., Lied, G. A. & Røseth, A. G. Exploring Gut Microbiota Composition as an Indicator of Clinical Response to Dietary FODMAP Restriction in Patients with Irritable Bowel Syndrome. Dig. Dis. Sci. 63, 429–436 (2018).