The invention relates to 4-hydroxyisoleucine, isomers, analogs, lactones, salts, and prodrugs thereof, to processes for their preparation, and to pharmaceutical compositions comprising the same. More particularly, the invention relates to the use of those compounds in the prevention and treatment of disorders of fat metabolism and related syndromes. The invention further relates to the use of those compounds in the prevention and treatment of obesity and related syndromes including, but not limited to, the cosmetic treatment of a mammal in order to effect a cosmetically beneficial loss of body weight, and more particularly loss of body fat.