THE TRANSITION FROM LIPID TO CARBOHYDRATE OXIDATION IN RESPONSE TO REFEEDING AFTER STARVATION

Carbohydrate re-feeding after prolonged starvation is associated with the delayed reactivation of the pyruvate dehydrogenase (PDH) complex i n skeletal muscle and other tissues. This paper seeks to establish whe ther, consistent with this delayed reactivation, there is a delay in t he transition from lipid- to carbohydrate-based fuel oxidation at the whole-body level in response to re-feeding. Chow re-feeding of 24 h-st arved rats is shown to be associated with a slow and multiphasic incre ase in respiratory quotient (RQ), full restoration of fed values takin g approximately 5 h. Dichloroacetate (DCA), an activator of PDH, incre ases 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 bein g 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 reactivati on of the PDH complex. The slow transition between lipid- and carbohyd rate-based fuel oxidation in response to refeeding may indicate the ex istence of a mechanism(s) to preferentially direct dietary carbohydrat e into muscle glycogen synthesis at the expense of lipid oxidation.