Of all the available strategies for improving irritable bowel syndrome (IBS) symptoms, diet is considered to play an important role in improving the quality of life of those affected by IBS. Although the gut microbiota and diet are being measured in current IBS-related nutrition studies, those studies usually include small samples and focus on energy and nutrients without considering the complex impact of overall dietary pattern on the microbiota.
Heidi Staudacher and colleagues examined diet-gut microbiota associations and the role of gut microbiota as a predictor of clinical response to a low FODMAP diet or probiotic intervention in 95 adults with IBS.
The authors measured habitual 7-day food record data not only at the nutrient level, but also in terms of foods, food groups and dietary patterns. They also measured gut microbiota composition using 16S ribosomal ribonucleic acid sequencing.
The study’s first goal consisted of identifying diet-gut microbiota associations in participants who consumed their habitual diet. Although an initial analysis found different associations between habitual diet—especially at the nutrient level—and gut microbiota abundances at genus, family and phylum level, none of those associations remained significant after correction for multiple comparisons.
The lack of associations could be explained by different interactions between diet and the gut microbiota in IBS when compared to healthy controls, highly personalized diet-gut microbiota interactions that could mask findings at group level, and operational taxonomic unit inclusion cut-off and statistical corrections that may have been too stringent, as Staudacher acknowledged in a Twitter thread.
The authors were also interested in exploring the impact on the gut microbiota of a low FODMAP diet or a multistrain probiotic administered over a 4-week period, based on authors’ preliminary data on the effect of restricting prebiotic substrates on the gastrointestinal microbiota in patients with IBS.
Although the baseline gut microbiota did not discriminate between responders and non-responders in terms of clinical response to either intervention—defined as a reduction in IBS symptomatology equal to or higher than a 50-point reduction in the IBS-Symptom Scoring System—specific changes in the gut microbiota were documented after both interventions.
Following a low FODMAP diet led to changes in the abundance of major saccharolytic genera, including higher Bacteroides and lower Bifidobacterium and unclassified genus in the Ruminococcaceae family compared to the control diet, in line with previous studies. No differences were observed in alpha diversity between low FODMAP and control diet groups.
Probiotic supplementation led to higher Lactobacillus and Streptococcus abundance compared to the placebo group. The authors argue that the probiotic intervention might help partly ameliorate the changes in gut microbial communities driven by the low FODMAP diet.
On the whole, the study shows that IBS patients’ gut microbiota could respond to diet or probiotics differently to that of healthy individuals. Although no significant associations have been found overall between nutrients, food intake and dietary patterns on the one hand and gut microbiota composition on the other, differences in the gut microbiota after the low FODMAP diet and probiotic intake highlight the importance of considering the complexity of diet (beyond focusing only on nutrients) in the role of gut microbiota for predicting response to interventions.
Staudacher HM, Scholz M, Lomer MC, et al. Gut microbiota associations with diet in irritable bowel syndrome and the effect of low FODMAP diet and probiotics. Clinical Nutrition. 2020. doi: 10.1016/j.clnu.2020.10.013.