The highest expression of ghrelin receptors is found within the brain.544,548 The central ghrelin signaling plays a pivotal role in diverse physiological functions, including the regulation of food intake, hippocampal synaptic plasticity and neurogenesis, anxiety, depression, and cognitive function.544,549–551 Notably, age-related reductions in ghrelin signaling have been associated with a decline in cognitive function.551 The gut microbiome, along with its metabolites, has been reported to modulate ghrelin secretion and CNS functions.552,553. This evidence concerns the gene GHRL and depressive symptom measurement.