Effects of fermented milk containing Lacticaseibacillus paracasei strain Shirota on constipation and gut microbiota: A randomised pilot study in Vietnam

Fermented milk containing Lacticaseibacillus paracasei strain Shirota (LcS) has been shown to improve stool consistency in various countries; however, its effect on hard or lumpy stools (HLS) in the Vietnamese population remains unclear. We investigated the effects of LcS-fermented milk on constipated Vietnamese adults with a high prevalence of HLS. In a single-centre, open-label trial, 51 participants with HLS were randomised to receive one bottle per day of fermented milk containing ≥6.5 × 109 cfu of LcS for 4 weeks (probiotic group) or no intervention (control group), followed by a 2-week washout. The primary endpoint was the proportion of participants with HLS (Bristol Stool Form Scale score of 1 or 2) in ≥25% of bowel movements over 4 weeks. Secondary endpoints included total stool frequency, HLS frequency, ideal stool form, and defecation-related symptoms - all recorded in daily diaries. The Chinese Constipation Questionnaire (CCQ) and gut microbiota composition (16S rRNA sequencing) were assessed every 2 weeks. During the intervention, the probiotic group had a significantly lower proportion of participants with HLS in ≥25% of bowel movements compared to controls (odds ratio: 0.00; 95% confidence interval: 0.00-0.16; P = 0.005). The probiotic group also showed increased total stool frequency ( P = 0.001), reduced HLS frequency ( P = 0.035), and fewer participants with CCQ scores ≥5 indicating constipation ( P < 0.001) at 4 weeks. Gut microbiota beta-diversity differed between groups after 2 weeks ( P = 0.031), with reductions in Peptococcaceae, Clostridium_methylpentosum_group, and Clostridia (unclassified at the order level), followed by increases in Lachnospiraceae_UCG-004 at 4 weeks and Lachnospiraceae_ND3007_group post-follow-up ( P < 0.050), suggesting microbial changes linked to constipation improvement. No serious adverse events related to the intervention were observed. These findings support daily LcS-fermented milk as a dietary strategy in Vietnam to manage constipation via gut microbiota modulation. The study was registered at ClinicalTrials.gov (ID: NCT05982743).