CRH and obesity due to melanocortin 4 receptor deficiency: Dysregulation in the gut microbiome can lead to obesity by altering the absorption of nutrients in the host, modifying metabolic pathways in the host and secreting bacterial metabolites that target the brain directly via vagal stimulation or indirectly through immune-neuroendocrine mechanisms involving corticotropin-releasing hormone, adrenocorticotropin and corticosterone (Geng et al., 2022; Tseng and Wu, 2019; Wang et al., 2020).