Abstract It has been documented that choline supplementation results in urinary conservation of carnitine in both humans and guinea pigs. This conservation in guinea pigs is associated with increased concentrations of carnitine in skeletal muscle for which no functional consequences have been reported. The objective of this study was to evaluate changes in fat metabolism and body composition as a consequence of the increased tissue carnitine in choline-supplemented guinea pigs. Guinea pigs were given free access to commercial diet without or with 3 g choline/kg diet. Using indirect calorimetry, the respiratory exchange ratios (RER) of the animals were determined under normal, exercise, and unfed conditions. There were no differences in RER between supplemented and nonsupplemented groups under any of the conditions. The RER data lead to the conclusion that choline–carnitine did not promote oxidation of fat over carbohydrates for energy. However, proximate analysis of carcass revealed significantly lower total body fat and higher body proteins in the choline-supplemented animals compared with the nonsupplemented animals. These apparently contradictory results are explained by the hypothesis that the acetates generated by the β-oxidation of fatty acids are transferred to carnitine and not oxidized to carbon dioxide, resulting in little or no shift in RER.