Table 2.

Key peptides and neurotransmitters involved in the regulation of energy intake (39).

	Stimulation of production site	Production inhibitors	Effects on the regulation of hunger	Effects on energy expenditure
Afferent system
Leptin	Post-prandial period	Fasting	Anorexigenic action	Increases
Ghrelin	Fasting/pre-prandial period	Post-prandial period	Orexigenic action	Decreases
Glucagon like-peptide -1 (GLP-1)	Post-prandial period	Fasting	Anorexigenic action	No effects
Insulin	Post-prandial period	Overnight fasting, preprandial period	Anorexigenic action	No effects
CNS system
Neuropeptide (NPY)	Fasting/Ghrelin	Leptin, glucose	Orexigenic action	Decreases
Agouti-related peptide protein (AgRP)	Fasting/Ghrelin	Leptin	Orexigenic action	Decreases
Melanin-concentrating hormone (MCH)	Flavors of food	Melanocyte-stimulating hormone (MSH)-producing neurons	Orexigenic action	No effects
Alpha-melanocyte-stimulating hormone (a-MSH)	Leptin	AgRP	Anorexigenic action	Increases
Efferent system
Irisin	Exercise, energy expenditure	Unknown	No direct effect on hunger	Increases
Serotonin/Norepinephrine	Environmental factors: low temperatures, diet, mood	Weight loss	Orexigenic action	Increases
Thyroid hormones	Low temperatures, high caloric diet	Critical illness, caloric restriction, drugs	Appetite variations according to hyper or hypothyroidism	Increases