Pathways Regulating Food Intake

Preabsorptive and postabsorptive signals from the gastrointestinal tract and changes in plasma nutrient levels provide short- and long-term feedback to regulate food intake:

• Gastrointestinal hormones (eg, glucagon-like peptide 1 [GLP-1], cholecystokinin [CCK], peptide YY [PYY]) reduce food intake.

• Ghrelin, secreted primarily by the stomach, increases food intake.

• Leptin, secreted from adipose tissue, informs the brain how much fat is stored. Leptin suppresses appetite in normal-weight people, but high leptin levels correlate with increased body fat. Leptin levels can decrease when weight is lost and then send a hunger signal to the brain.

The hypothalamus integrates various signals involved in the regulation of energy balance and then activates pathways that increase or decrease food intake:

• amphetamine-related transcript (CART), orexin, and melanin-concentrating hormone (MCH) increase food intake.

• Corticotropic hormone (CRH) and urocortin decrease it.