Background Chronic constipation affects approximately 14% of adults worldwide and is closely linked to sleep disturbances and anxiety through the gut–brain axis, with diet playing a significant role in its onset and progression. This study isolated and characterized indigenous lactic acid bacterial strains from Inner Mongolia and Tibet, and evaluated a novel multi-strain fermented yogurt (containing patented probiotic strains, designated K-10) in a clinical trial. Methods Primary and secondary outcomes included constipation severity (assessed by the Cleveland Clinic Score (CCS) and the Patient Assessment of Constipation Symptoms (PAC-SYM)), quality of life (Patient Assessment of Constipation Quality of Life (PAC-QOL)), anxiety (Generalized Anxiety Disorder-7 (GAD-7)), sleep quality (Pittsburgh Sleep Quality Index (PSQI)), systemic inflammatory markers (tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6)), oxidative stress indicators (superoxide dismutase (SOD), malondialdehyde (MDA), total antioxidant capacity (T-AOC), and catalase (CAT)), sleep-related factors (serotonin (5-HT), cortisol, melatonin (MT), and dopamine (DA)), and gut microbiota composition analyzed via 16S ribosomal RNA (rRNA) gene sequencing. Results The K-10 group showed significant improvements in constipation symptoms, as reflected by a reduction in the CCS score to below 15 ( P < 0.001). Additionally, this intervention alleviated anxiety, with fewer participants experiencing moderate-to-severe anxiety. Although no significant between-group difference was found in the total PSQI score, sleep quality was improved specifically in sleep latency and hypnotic drug dependence, with significant differences between groups (both P < 0.05). Notably, consumption of K-10 yogurt significantly increased the abundance of beneficial Bacteroides species and elevated the production of short-chain fatty acids (SCFAs), particularly butyrate and acetate ( P < 0.05). These microbial changes were associated with reduced systemic inflammation, as indicated by lower levels of TNF-α and IL-6, and improved antioxidant status, reflected by enhanced SOD activity and T-AOC. Conclusion Compared to conventional yogurt, the novel multi-strain fermented K-10 yogurt effectively alleviates constipation, anxiety, and poor sleep quality, while simultaneously reducing inflammation and oxidative stress. These benefits appear to be mediated by alterations in the gut microbiota, specifically through the enrichment of Bacteroides and the increased SCFAs production. The findings underscore the potential of K-10 yogurt as a functional food for the management of functional constipation and its common psychiatric comorbidities.
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