Pharmaceutical compositions are disclosed comprising one or more compounds selected from the group consisting of phenylacetylglutamine, phenylacetylisoglutamine, and phenylacetic acid, in addition to pharmaceutically-acceptable salts, analogs, and precursors thereof, and optionally also isoglutamine, with a pharmaceutically-acceptable carrier, diluent, or excipient, useful in the treatment or prevention of hypercholesterolemia and hypertriglyceridemia. Also disclosed are methods for treating or preventing hypercholesterolemia and hypertriglyceridemia using the pharmaceutical compositions.