Effects and Persistence of Bifidobacterium animalis subsp. lactis BL-99 and Fructooligosaccharides on Older Adults with Functional Constipation: A Randomized, Double-Blind, Placebo-Controlled Trial

Research on effects of synbiotics in older adults with functional constipation (FC) is limited. This randomized, double-blind, placebo-controlled trial evaluated a 4-week synbiotic (Bifidobacterium animalis subsp. lactis BL-99 and fructooligosaccharides [FOS]) intervention in 67 participants ≥60 years old meeting Rome IV FC criteria. Compared to placebo, the synbiotic group showed significant improvements in weekly spontaneous bowel movements (Least squares mean ± standard error: 4.94 ± 0.25 vs. 3.00 ± 0.26, P < 0.001) and whole gut transit time (37.13 ± 3.78 vs. 50.64 ± 4.22 h, P = 0.019), with benefits sustained 2 weeks post-intervention. It also reduced time per toilet attempt and alleviated rectal discomfort symptoms more effectively than placebo. Fecal microbiome analysis revealed increased abundance of beneficial Bifidobacterium species, correlating with symptom improvement (P < 0.05). These findings demonstrate that BL-99/FOS supplementation ameliorates FC symptoms in older adults, with effects sustained post-discontinuation, potentially mediated through gut microbiota modulation. Further mechanistic investigation is warranted.