Effect of Daily Consumption of a Fermented Milk Containing Lacticaseibacillus paracasei Strain Shirota (LcS) on Stool Consistency in United States Adults with Hard or Lumpy Stools: A Randomized Controlled Trial

BACKGROUND: Lacticaseibacillus paracasei strain Shirota (LcS) has shown benefits for stool consistency in populations with certain bowel complaints (e.g., constipation), but data in a United States population are limited. OBJECTIVES: This study evaluated the effects of LcS on hard or lumpy stools (HLS) in an otherwise healthy population that generally represents the United States adult demographic. METHODS: colony forming units LcS/mL for 28 d (active group) or no intervention (control group) followed by a 14-d postintervention period. Bowel habits were recorded daily using a novel smartphone application. The primary endpoint was the presence of HLS in ≥25% of the participant-rated BMs using the Bristol Stool Form Scale over the 28-d intervention. Secondary endpoints included the presence of reduced frequency of BMs with HLS from baseline, stool frequency, straining, incomplete evacuation, artificial intelligence-derived stool image scores, and Patient Assessment of Constipation Quality of Life (PAC-QOL) scores. RESULTS: The active group showed a significantly lower proportion of participants with HLS in ≥25% of BMs [odds ratio: 0.34; 95% confidence interval (CI): 0.14, 0.80; P = 0.014] along with a higher proportion of participants with a reduced frequency of BMs with HLS from baseline (odds ratio: 2.86; 95% CI: 1.03, 7.92; P = 0.043). The active group also demonstrated positive improvements in total PAC-QOL scores (P = 0.003). CONCLUSIONS: Daily consumption of LcS-containing fermented milk significantly reduced constipation symptoms and improved quality of life in an otherwise generally healthy United States adult population with a history of intermittent BMs producing HLS. The intervention was well tolerated, with no serious adverse events related to the product, suggesting its safety and potential as a dietary strategy for managing constipation. TRIAL REGISTRATION NUMBER: This trial was registered at clinicaltrials.gov as NCT06014008 (https://clinicaltrials.gov/study/NCT06014008).