Gut-brain connection in schizophrenia: A narrative review

Table 1 Overview of the roles and implications of various gut hormones and neuropeptides in appetite regulation, energy balance, and mood

Hormone/ neuropeptide	Source	Function	Mechanism of action	Clinical implications
Ghrelin	Stomach	Stimulates appetite	Activates neurons in the hypothalamus; levels increase before meals and decrease afterward	Implicated in meal initiation; dysregulation linked to impulsivity and risk-taking behaviors in schizophrenia
Leptin	Adipose tissue	Inhibits hunger	Signals the brain regarding energy stores; reduces appetite	Dysregulation associated with obesity and metabolic disorders
Peptide YY	Small intestine	Promotes satiety and reduces food intake	Secreted postprandially; acts on the hypothalamus	Linked to appetite regulation; imbalances can affect weight management
Glucagon-like peptide 1	Intestines	Promotes satiety; enhances insulin secretion	Acts on receptors in the brain; improves glucose homeostasis	Neuroprotective effects; may counteract Alzheimer’s disease progression by enhancing memory and reducing neuroinflammation
Serotonin	Gut (90% produced)	Regulates motility, secretion, vascular tone, mood, cognition	Alters motility and secretion; regulates mood and emotional states	Alterations linked to depression, anxiety, and irritable bowel syndrome
Neuropeptide Y	Brain	Increases food intake; reduces anxiety-like behavior	Stimulated by stress and fasting; acts on receptors in the brain	Imbalances associated with eating disorders and stress-related behaviors