Effects of heat-killed Bifidobacterium longum KABP-042 and Lactiplantibacillus plantarum KABP-051 on cognitive performance in typically developing school-aged children: a placebo-controlled, randomized double-blind parallel-group trial

Background Increasing evidence suggests that the gut-brain axis plays a critical role in cognitive and behavioral development. However, clinical evidence supporting cognitive benefit of probiotics and postbiotics in typically developing children remains limited. This study evaluated the effects of a postbiotic formulation containing heat-killed Bifidobacterium longum KABP-042 and Lactiplantibacillus plantarum KABP-051 on brain-related outcomes in school-aged children. Methods This study randomly allocated 60 typically developing children (aged 8–10 years) to receive either a daily jelly containing heat-killed KABP-042 and KABP-051 (5 × 10 9 cells each) or a placebo for 12 weeks. The primary endpoints were changes in working memory (digit span), inhibitory control (Go/No-go task), and cognitive flexibility measured by the Stroop test. Secondary endpoints included autonomic nervous system (ANS) activity, emotional and behavioral assessment, and gut microbiota composition. Results Participants who received the postbiotic intervention demonstrated significantly higher accuracy ( p = 0.019) and lower error rates ( p = 0.004) in the incongruent condition of the Stroop test at 12 weeks compared to placebo, while reaction time was unchanged. No significant between-group differences were observed in working memory, inhibitory control, ANS activity, emotional and behavioral outcomes, and gut microbiota composition, although changes in beta diversity were significantly greater in the placebo group ( p = 0.049). Conclusions Twelve weeks of postbiotic intervention was associated with enhanced accuracy-related Stroop task performance, particularly in the incongruent condition, in typically developing children, whereas other cognitive outcomes were unaffected. These preliminary findings suggest that supplementation with KABP-042 and KABP-051 may influence selected aspects of cognitive task performance in children. Further investigation into the underlying mechanisms and long-term outcomes is warranted. Trial registration This study was registered with the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR; ID: UMIN000058366).