Effects of Lacticaseibacillus paracasei 327 intake on the intestinal environment in healthy adult Japanese: a randomized, double-blind, placebo-controlled, parallel-group trial

Background: Lacticaseibacillus paracasei 327 (L. paracasei 327) is a lactic acid bacteria isolated from brown rice. It has been reported that sterilized L. paracasei 327 improves bowel movement. Given the reported relationship between intestinal microbiota and bowel movement, we hypothesized that L. paracasei 327 also improves the intestinal environment through its involvement in fluctuations in the composition of the intestinal microbiota. Objective: The purpose of this study was to verify the effects of the consumption of food containing sterilized L. paracasei 327 on the intestinal environment in healthy Japanese adults. Methods: A randomized, double-blind, placebo-controlled, parallel-group trial was conducted in 110 healthy adults aged 20 to 64 years with a defecation frequency of three to five times per week. Participants were divided into two groups, one receiving 25 mg (approximately 5x1010 bacteria) of sterile L. paracasei 327 once daily for two weeks (55 participants) and other receiving placebo for two weeks (55 participants), to test its effect on the intestinal environment. Results: Intestinal microbiota analysis showed that L. paracasei 327 ingestion resulted in a trend towards an increase in Bacteroides and a significant decrease in Clostridium cluster IV in each taxonomic group compared to the placebo group. In addition, for each operational taxonomic units (OTUs), Bacteroides_OTU_469 and Clostridium subcluster XIVa_OTU_754 were significantly increased, and Clostridium cluster IX, Akkermansia_OTU_110 tended to increase, while Clostridium cluster IV_OTU_749 significantly decreased. Furthermore, defecation days and defecation frequency increased significantly. Conclusion: The presumptive species of bacteria in the taxonomic group and OTUs increased by L. paracasei 327 ingestion included short-chain fatty acid-producing bacteria. In addition, Clostridium cluster IV_OTU_749, which was reduced by L. paracasei 327 ingestion, may also be involved in the production of putrefactive products in the intestine. Therefore, these findings suggest that L. paracasei 327 ingestion improves the intestinal environment by increasing short-chain fatty acid-producing bacteria, suppressing putrefactive-producing bacteria, and improving defecation. Trial registration: UMIN000049859 (UMIN-CTR)Keywords: Lactic acid bacteria; Postbiotics; Lacticaseibacillus paracasei 327; Intestinal microbiota; Defecation; Clinical trial