By Jun Kim Ph.D.
It was previously discussed [IBS, Sibo, Probiotics] that one of the investigated observations in irritable bowel syndrome (IBS) involves small intestinal bacterial overgrowth (SIBO). Another common parameter that is used to characterize the pathophysiology of IBS is alterations in gut motility. Gut motility is the stretching and contractions of the muscles in the gastrointestinal (GI) tract, and it controls the movement of food throughout the digestive tract. The synchronized contraction of these muscles is called peristalsis. Abnormal motility patterns can lead to bloating, pain, nausea, diarrhea, and constipation, all of which are symptoms related to IBS.
Gut motility can be characterized by the migrating motor complex (MMC), which is a distinct pattern of electromechanical activity observed in gastrointestinal smooth muscle. During MMCs, there are periodic, luminal contractions that push intestinal contents from the stomach to the last part of the small intestine, the ileum. Several studies have shown that IBS patients can have abnormal MMC. For example, Vassallo et al. showed that IBS patients had stronger and longer contractions more frequently, which reflects the increased perception of pain . Another study showed that patients with diarrhea-predominant IBS had accelerated transit of intestinal contents to the colon .
Changes in gut motility can be divided into three categories based on the symptoms of IBS: (i) diarrhea-type, (ii) constipation-type, and (iii) pain-type . In diarrhea-type, it has been noted that there are increased contractions after food ingestion, increased propagating contractions, decreased intestinal transit time, and rapid evacuation of intestinal contents [4–6]. In constipation-type, decreased propagating contractions of the colon, longer transit time, and rapid evacuation have been shown [5–8]. In pain-type, contractions have been shown to be more concentrated in jejunum and ileus with significantly larger propagating contractions during abdominal pain and anorectal sensitivity disorder [9–12].
Multiple studies suggest the importance of gut microbiota in gut motility. Bifidobacterium and Lactobacillus were less abundant in adult patients with constipation [13, 14]. However, other studies showed an increased abundance of Bifidobacterium or abundance changes in other species [15, 16]. Such contrasting outcomes suggest that the association between gut motility and gut microbiota may depend on the patient demographics and is species-specific. Furthermore, it is important to note that the alterations in gut microbiota can be either a cause or a result of the conditions. For example, when mice with human gut microbiota were induced to have faster intestinal content transit using different methods, they had similar changes in gut microbiota composition, suggesting that changes in GI transit can affect the composition of the microbial community .
Studies that associate gut motility and gut microbiota may suggest that taking probiotics influences gut motility. Indeed, studies have shown that taking probiotics such as Bifidobacterium animalis and Bifidobacterium lactiscan accelerate intestinal transit and improve symptoms in constipation-type patients [18–20]. However, the outcomes seemed to depend on the probiotic species as some probiotics have shown to decrease bowel movements, and improve loose stool in diarrhea-type patients [21, 22]. The species-dependent response was demonstrated in a study where intestinal bacteria promoted or suppressed MMC in rat models depending on the species . Although currently not available, a systematic comparison of the species-specific effect of probiotics on gut motility is needed for more consistent results. It would be very interesting to see whether a certain combination of probiotic species can both increase and decrease bowel movements depending on conditions and be effective for all three categories of the symptoms.
Disclaimer: The above article is sponsored by Thryve, the world’s first Gut Health Program that incorporates microbiome testing and personalized probiotics to ensure a healthier gut, happier life, and a brighter future.
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