Shortens duration of eating, without affecting rate of eating. Biosynthesized from essential amino acid tryptophan, hence plasma Trp concentrations affect serotonin concentrations in brain. Tryptophan is present in most foods in relatively small amounts, hence protein-rich meal results in decrease in relative amount of Trp relative to other amino acids, and hence decreased serotonin production. Unproven and controversial hypothesis. But administration of tryptophan alone has little effect on food selection.
Morphine increases fat preference in rats.
Site of action apparently in hypothalamus. Williams and Wilkins, Baltimore.