Gamma-aminobutyric acid (GABA) is a key inhibitory neurotransmitter in the central nervous system, and recent research suggests it may act as a mediator in the gut-brain axis. While traditionally believed not to cross the blood-brain barrier, evidence indicates that changes in GABA levels and gut microbiota composition influence mental health. GABA is produced by various organisms, including humans, plants, and bacteria, and is synthesized from glutamate via the glutamic acid decarboxylase (GAD) enzyme. GABA-producing bacteria such as Bifidobacterium, Lactobacillus, and Bacteroides are prevalent in the human gut and can influence mental health conditions like anxiety, depression, and autism spectrum disorder. GABA is also involved in peripheral functions, such as pancreatic health. GABA is produced by gut microbiota and can be influenced by dietary factors, probiotics, and prebiotics. Studies show that GABA-producing bacteria, such as Bacteroides fragilis, can increase GABA levels in the gut and brain, potentially improving mental health. Additionally, homocarnosine, a GABA-containing brain peptide, may play a role in GABA metabolism and brain function. Research indicates that homocarnosine can act as a GABA reservoir and contribute to glutamate-GABA cycling in the brain. GABA-producing microorganisms, including those from fermented foods, have been identified as potential agents for treating neurological and psychological disorders. Dietary factors, such as enzymes from Aspergillus and Penicillium, can enhance GABA production in the gut. Probiotic supplementation and prebiotic factors may improve cognitive function, reduce anxiety, and increase GABA availability in the brain. Overall, GABA and its metabolites, including homocarnosine, are increasingly recognized as important mediators in the gut-brain axis, with potential applications in mental health and neurological disorders. Further research is needed to fully understand the role of GABA and homocarnosine in brain function and to develop targeted interventions.Gamma-aminobutyric acid (GABA) is a key inhibitory neurotransmitter in the central nervous system, and recent research suggests it may act as a mediator in the gut-brain axis. While traditionally believed not to cross the blood-brain barrier, evidence indicates that changes in GABA levels and gut microbiota composition influence mental health. GABA is produced by various organisms, including humans, plants, and bacteria, and is synthesized from glutamate via the glutamic acid decarboxylase (GAD) enzyme. GABA-producing bacteria such as Bifidobacterium, Lactobacillus, and Bacteroides are prevalent in the human gut and can influence mental health conditions like anxiety, depression, and autism spectrum disorder. GABA is also involved in peripheral functions, such as pancreatic health. GABA is produced by gut microbiota and can be influenced by dietary factors, probiotics, and prebiotics. Studies show that GABA-producing bacteria, such as Bacteroides fragilis, can increase GABA levels in the gut and brain, potentially improving mental health. Additionally, homocarnosine, a GABA-containing brain peptide, may play a role in GABA metabolism and brain function. Research indicates that homocarnosine can act as a GABA reservoir and contribute to glutamate-GABA cycling in the brain. GABA-producing microorganisms, including those from fermented foods, have been identified as potential agents for treating neurological and psychological disorders. Dietary factors, such as enzymes from Aspergillus and Penicillium, can enhance GABA production in the gut. Probiotic supplementation and prebiotic factors may improve cognitive function, reduce anxiety, and increase GABA availability in the brain. Overall, GABA and its metabolites, including homocarnosine, are increasingly recognized as important mediators in the gut-brain axis, with potential applications in mental health and neurological disorders. Further research is needed to fully understand the role of GABA and homocarnosine in brain function and to develop targeted interventions.