Irritable bowel syndrome (IBS) is a common disorder characterized by abdominal pain, bloating, and changes in bowel habits. The role of the gut microbiota in IBS has been increasingly recognized, and several studies have identified alterations in the gut microbial composition and function in IBS patients.
In a study by Tap et al. (2017), the authors identified an intestinal microbiota signature associated with the severity of IBS using 16S rRNA gene sequencing. They found that IBS patients had a distinct microbiota composition compared to healthy controls, with lower relative abundances of several butyrate-producing bacteria, including Faecalibacterium, Roseburia, and Eubacterium. In a follow-up study, Bennet et al. (2018) found that IBS patients had an altered intestinal antibacterial gene expression response profile, which was linked to bacterial composition and immune activation.
The gut microbiota may also play a role in the secretion of chromogranins and secretogranins, which are markers of enteroendocrine cells in the gut. Sundin et al. (2018) found that fecal levels of chromogranins and secretogranins were linked to the fecal and mucosal bacterial composition of IBS patients and healthy subjects.
The gut microbiota has also been linked to brain functional connectivity and gastrointestinal sensorimotor function in IBS patients. Labus et al. (2019) used tripartite network analysis to show an association between gut microbial Clostridia and brain functional connectivity in IBS patients.
Le Nevé et al. (2019) examined the role of the gut microbiota in the response to a fermented milk product in IBS patients. They found that fasting breath hydrogen and the metabolic potential of the gut microbiota were associated with the response to the fermented milk product. In a separate study, Le Nevé et al. (2020) found that a fermented milk product containing Bifidobacterium lactis CNCM I-2494 and lactic acid bacteria improved gastrointestinal comfort in response to a challenge diet rich in fermentable residues in healthy subjects. The effects of the fermented milk product on the gut microbiota were further investigated in a metatranscriptomic analysis by Oyarzun et al. (2022). They found that the fermented milk product mitigated the effects of a flatulogenic diet on gas-related symptoms in several ways, including the depletion of gas-producing bacteria and increased hydrogen to methane conversion, upregulation of certain metabolic activities, and a more connected microbial ecosystem.
Nevé et al. (2020) also examined the effects of a fermented milk product containing Bifidobacterium lactis CNCM I-2494 on the tolerance of a plant-based diet in patients with disorders of gut-brain interactions (DGBI), which include IBS and functional dyspepsia. They found that the fermented milk product improved tolerance to a plant-based diet in these patients, as well as reducing gastrointestinal symptoms and exhaled hydrogen.
The diet-microbiota-symptom interactions in IBS were further explored in a study by Tap et al. (2021). The authors used a food diary and shotgun metagenomic analysis to examine the diet and gut microbiome in 149 IBS patients and 52 healthy controls. They found that individuals with severe IBS had a higher intake of poorer-quality food items during main meals and that covariations between the gut microbiota at the subspecies level and diet could be explained by IBS symptom severity, exhaled gas levels, glycan metabolism, and the ratio of meat to plant intake. They also found evidence that IBS severity is associated with altered gut microbiota hydrogen function, which is correlated with microbiota enzymes involved in animal carbohydrate metabolism.
Polster et al. (2021) used a novel integrative analysis pipeline to examine the microbiota-host interactions and their link to symptoms in IBS. They found that there were distinct differences in the gut microbiota of IBS patients compared to healthy controls and that these differences were associated with specific IBS symptoms.
In summary, several studies have identified alterations in the gut microbiota composition and function in IBS patients and have provided evidence for the role of the microbiota in IBS symptoms. Some studies have also shown that fermented products, such as fermented milk products, may have a beneficial effect on IBS symptoms and the gut microbiota in IBS patients. However, more research is needed to fully understand the mechanisms underlying these associations and to determine the optimal fermented products and probiotic strains for the management of IBS symptoms. Targeted therapies targeting the gut microbiota may also be a promising approach for the management of IBS.
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