Randomized controlled trials (RCTs) of fecal microbiota transplantation (FMT) in patients with irritable bowel syndrome (IBS) have produced outcomes varying from no effect at all to high efficacy and durable effects over time. This review analyzed differences in the protocols used in FMT RCTs for IBS in the recently published literature with the aim of identifying the factors responsible for the success or failure of these RCTs. The results of this analysis might be useful in formulating an effective standard protocol for FMT in IBS. A systematic search was conducted in the PubMed database of the literature published in English from January 2015 to December 2023 using several search phrases comprising MeSH expressions. Those RCTs that carefully selected donors based on environmental factors that are known to affect the gut microbiota positively and ensured bacterial diversity before and during FMT produced successful outcomes. Furthermore, direct freezing of the donor's fecal transplant, storing it at -80°C until the FMT is performed, and then thawing it at 4°C and mixing it manually appear to be factors associated with the success of FMT in IBS. Administering the donor's fecal transplant into the small intestine results in durable effects of FMT and long-term colonization of beneficial bacteria. A standard protocol for FMT with large and durable effects should include (1) careful donor selection, (2) handling the donor's fecal transplant in a way that preserves its microbiota contents, and (3) administering the transplant into the small intestine.
El-Salhy et al. (Sat,) studied this question.