Studies investigating fat as a fuel for exercise have found that increasing free fatty acids during exercise tends to spare muscle glycogen due to increased utilization of free fatty acids for energy, which in turn can enhance the capacity for endurance exercise. Medium-chain triglycerides do not delay gastric emptying or absorption. They are broken down by lipase in the stomach and duodenum to glycerol and medium-chain fatty acids (MCFA). Since MCFAs are metabolized as quickly as glucose, it has been speculated that they might provide an alternative carbon source for the muscle during prolonged exercise. While the majority of studies investigating the role of medium-chain triglycerides and exercise have found no sparing effect of muscle glycogen after consumption of medium-chain triglycerides, two recent studies have presented conflicting results. This review will investigate the speculated role of medium-chain triglycerides as an alternative fuel source for exercising muscles and will discuss the possibility that medium-chain triglycerides preserve muscle glycogen during exercise,
J.R. Beming is with the University of Colorado at Colorado Springs, Department of Biology, 1420 Austin Bluffs Parkway, Colorado Springs, CO 80933.