Fasting glucose synthesis

As we have seen, normally pyruvate would be the substrate for pyruvate dehydrogenase complex to form acetyl-CoA, but during fasting in the absence of glucose, acetyl -CoA for the TCA cycle is derived from fatty acid (3-oxidation (see Section 7.5.2) so pyruvate is diverted into oxaloacetate by the enzyme pyruvate carboxylase. Thus any amino acids whose carbon skeletons can be converted into pyruvate, OAA or another substrate of the TCA cycle, can be used for glucose synthesis. 

Oxaloacetate is the precursor for glucose synthesis in the fasting state (section... 

B. In its critical role as the central organ for synthesis and distribution of fuel molecules, the liver is mainly focused on export of glucose to peripheral tissues during a short-term fast. 

A. If fasting extends past 1-2 days, which is considered to be a long-term fast or starvation, further changes in fuel synthesis and use by several organs can occur, principally a conversion from a glucose economy to one dominated by ketone bodies as fuel (Figure 5—6). 

Reduction of oxaioacetate synthesis aiso impairs gluconeogenesis, which compromises tissues dependent on glucose metabolism (such as the brain) during fasting. 

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