Fatty Acid Metabolism during Exercise

Abstract

Obesity-induced metabolic syndrome is becoming a severe health problem in Japan due to the increasing popularity of the Western-style diet and fast food. Endurance exercise is one of the most effective ways to reduce fat content and thus prevent metabolic syndrome, as endurance exercise leads to larger amounts of fatty acids being used to create energy with higher efficiency in skeletal muscle. There are two major types of skeletal muscle fibers: type I muscle fibers, which contain a large number of mitochondria and burn fatty acids for energy, and type II fibers, which contain fewer mitochondria and depend on glycolysis to acquire energy. Endurance exercise results in the development of type I muscle fibers and enhanced mitochondrial function, with increased expression and activity of mitochondrial enzymes such as carnitine palmitoyltransferase 1, β-hydroxy-acyl-CoA dehydrogenase and citrate synthase. On the other hand, in adipose tissues, higher amounts of fatty acids are released to support their increased usage in muscle fibers by increasing the activity levels of adipocyte triglyceride lipase and hormone-sensitive lipase following endurance exercise. The increased usage of fatty acids is considered an outcome of activated peroxidase proliferator-activated receptors (PPARs), nuclear receptors for fatty acids, and the induced transcription of proteins that play essential roles in fatty acid metabolism upon stimulation of those fatty acids. In three PPAR isoforms, muscle fibers predominantly express PPARγ, a regulator of mitochondrial enzyme transcription and type I muscle fiber development. In adipocytes, PPARγ is abundantly expressed to regulate fatty acid catabolism. Furthermore, skeletal muscles, adipose tissues and other tissues communicate through hormones such as myokines and adipokines, which optimize fatty acid metabolism in the entire body during endurance exercise. Collectively, endurance exercise shifts our energy metabolism to be more lipolytic for a healthier lifestyle.