How does your microbiome influence your behavior and personality?

The answer

The human microbiome contains approximately 38 trillion bacteria - slightly outnumbering human cells. These organisms produce neurotransmitters, short-chain fatty acids, and immune signals that directly affect brain function. Germ-free mice raised without microbiomes show dramatically altered behavior: increased risk-taking, reduced social interaction, and abnormal stress responses, which normalize after microbial colonization. A 2022 study in Nature Genetics found that gut microbiome composition explains more variation in blood metabolites than human genetics. Specific bacterial species influence food cravings by releasing hormones that hijack vagus nerve signaling. Research at UCLA showed that women consuming probiotic yogurt for four weeks showed measurably reduced brain reactivity to negative emotional stimuli.