The transition from lipid to carbohydrate oxidation in response to re- feeding after starvation

Carbohydrate re-feeding after prolonged starvation is associated with the delayed reactivation of the pyruvate dehydrogenase (PDH) complex in skeletal muscle and other tissues. This paper seeks to establish whether, consistent with this delayed reactivation, there is a delay in the transition from lipid- to carbohydrate-based fuel oxidation at the whole-body level in response to re-feeding. Chow re-feeding of 24 h-starved rats is shown to be associated with a slow and multiphasic increase in respiratory quotient (RQ), full restoration of fed values taking approximately 5 h. Dichloroacetate (DCA), an activator of PDH, increases RQ in starved rats and accelerates the increase in RQ in response to chow re-feeding. Chow re-feeding results in glycogen deposition in oxidative and non-oxidative skeletal muscles, glycogen repletion being essentially complete well before RQ has been restored to fed values. Two factors are identified as being determinants of RQ, the relative availabilities of glucose and lipid fuels and the extent of reactivation of the PDH complex. The slow transition between lipid- and carbohydrate-based fuel oxidation in response to re-feeding may indicate the existence of a mechanism(s) to preferentially direct dietary carbohydrate into muscle glycogen synthesis at the expense of lipid oxidation.