MBSFL alleviates constipation in mice by modulating the gut microbiota-5HT axis: it enhances intestinal motility via upregulating 5HTR4 and downregulating SERT expression, while restoring microbial diversity to favor short-chain fatty acid-producing genera (e.g., Lactobacillus and Bifidobacterium). The gene discussed is HTR5A; the disease is constipation disorder.