A joint research team from Azabu University, Kitasato University, Kyushu University, Kyoto University, Hirosaki University, and Tokai University has revealed that eicosapentaenoic acid (EPA), a type of fatty acid found in fish oil, increases the proportion of slow-twitch muscle types in rat skeletal muscles, and has the effect of improving whole-body lipid metabolism and muscle function.
Muscle fibers, the cells that make up skeletal muscle, are broadly divided into "slow-twitch" types that excel at lipid metabolism and do not fatigue easily, and "fast-twitch" types that excel at sugar metabolism and fatigue easily. The composition of muscle fiber types (the ratio of slow-twitch and fast-twitch) is an important factor that determines the metabolic characteristics of skeletal muscle, and it is said that increasing the ratio of slow-twitch types has benefits such as creating a body that is more likely to burn lipids and being more resistant to fatigue (improving endurance).
The research team previously found that fish oil intake increases the proportion of slow-twitch muscle fibers in rats, but the mechanism behind this was unclear. Therefore, in this study, they investigated the involvement of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are characteristic omega-3 fatty acids contained in fish oil.
As a result, it was found that EPA has high agonist activity against the nuclear receptor PPARδ, which is a key factor that controls the formation of slow muscle types and lipid metabolism in skeletal muscles. On the other hand, this activity was not confirmed with DHA. When EPA was administered to rats for four weeks, it was found that whole-body energy metabolism was promoted and muscle function was improved. As the background to this effect, it was found that the proportion of slow muscle types in the extensor digitorum longus and plantaris muscles was significantly increased.
A comprehensive analysis of the mechanism of action on genes and metabolites also revealed that EPA supplementation activates the PPARδ and AMP-activated protein kinase pathways in muscle cells. These results suggest that ingesting fish oil rich in EPA may induce effects similar to those of exercise training, such as enhancing lipid burning and acquiring an anti-fatigue constitution. The results of this research are expected to contribute to the fields of health science and sports science.
Paper information:【iScience】Eicosapentaenoic acid increases proportion of type 1 muscle fibers through PPARδ and AMPK pathways in rats
