This paper by Moro et al. reviewed the determinants of intramyocellular triglyceride (IMTG) turnover, i.e., the factors controlling the dynamic balance between lipolysis and lipid synthesis. The review paid particular attention to muscle oxidative capacity, IMTG breakdown (lipolysis) and synthesis, and plasma free fatty acid (FFA) availability, which are principal factors controlling the rate of IMTG turnover. The authors pointed out two different pathways that could lead to increased IMTG turnover (a functional adaptation to increased energy demand and the attempt to buffer a mismatch between lipid supply and oxidation). They proposed that a mismatch between IMTG lipolysis and mitochondrial B-oxidation increases intracellular lipid trafficking to the detriment of insulin signalling and glucose metabolism. Similar to its effect in athletes, who have a high IMTG turnover rate, regular physical activity could protect against FFA-induced insulin resistance in muscle by improving both lipid partitioning toward the IMTG pool and mitochondrial oxidative capacity. However, additional studies are clearly required to better understand the relationship between the IMTG turnover rate and the accumulation of toxic lipid intermediates in the pathophysiology of insulin resistance.
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