13C-labelled palmitate and metabolomics/lipidomics analyses reveal the fate of free fatty acids in fasting mice

Aims: During fasting, free fatty acids (FFA) released from adipose triglyceride stores become the major source of energy. Because lipolysis is in excess over utilization, plasma FFA are considerably elevated despite an increased utilization by skeletal muscle and other peripheral tissues. The plasma concentration of acylcarnitines, intermediates of fatty acid oxidation, also increases during fasting and exercise, but it is unclear if they originate from skeletal muscle or from the liver, the key metabolic regulator and short-term buffer for excess circulating FFA. Using a stable 13C-isotope labelled fatty acid t…