Previous investigators have studied the interactions of various diets and lipid deposition in healthy, physically-fit subjects, providing insight into the relationship between lipid deposition and diet. While high-fat diets have been associated with increased intramyocellular lipid (IMCL) deposition and high-carbohydrate diets have been shown to influence intrahepatic lipid deposition (IHL), high-protein diets may be related to decreased IHL deposition. Although it is understood that excess free fatty-acid (FFA) influx contributes to tissue lipid deposition, the influence of diet remains unresolved. Studying the interaction of diet and lipid deposition in subjects with an inherited defect in the fatty acid oxidation pathway provided a unique opportunity to examine relationships between mitochondrial function, accumulation of fatty-acid oxidation intermediates, differences in dietary intake and the effects of these changes on body composition. Preliminary data demonstrated that patients with Long-chain 3-Hydroxy Acyl-CoA dehydrogenase (LCHAD) deficiency had higher total body fat and extramyocellular (EMCL) lipid deposition, but similar levels of IMCL and IHL compared to controls. This study addressed whether impaired fatty acid oxidation (FAO) influences the deposition of IHL and IMCL.