Figure 1.

Factors affecting energy balance and thus steady-state weight. There are three main groups of factors—homoeostatic, environmental and behavioural processes—that interact and influence steady-state body weight. Alterations in any of these factors will result in changes to this steady-state and could result in obesity. AgRP, agout-related peptide; GIP, gastric inhibitory polypeptide; GLP-1, glucagon-like peptide-1; CART, cocaine- and amphetamine-regulated transcript; CCK, cholecystokinin; PYY, peptide YY; NPY, neuropeptide Y; POMC, pro-opiomelanocortin; PP, pancreatic polypeptide; REE, resting energy expenditure; NREE, non-resting energy expenditure. ‘Central' and ‘peripheral' refer to the site where the molecules are produced, rather than where they necessarily act. In gthe brain, insulin acts as an anorexigenic hormone.^{13, 104, 105} However, in the periphery, insulin lowers blood sugar, which potently stimulates food intake.¹⁰⁶