<META NAME=\"author\" CONTENT=\"歩 深澤\">
Purpose:
Long-term intake of very low-carbohydrate, high-fat (ketogenic) diets enhance production and utilization of ketone bodies, which are more energy-efficient fuels for skeletal muscle. However, adaptation to the extremely low-carbohydrate diet has been shown to upregulate pyruvate dehydrogenase kinase 4 (PDK4) content in skeletal muscle, which is a negative regulator of glycolytic flux, resulting in the impaired high-intensity exercise capacity. Because medium-chain triglyceride (MCT) can produce more ketone bodies than long-chain triglyceride (LCT), incorporating MCT into the diet may allow more carbohydrates yet preserving ketosis and exert less inhibitory effect on muscle glucose metabolism. The purpose of this study was therefore to examine the effects of long-term feeding of ketogenic diet containing MCT on the endurance training-induced adaptations in metabolic enzymes of rat skeletal muscle.
Methods:
Male Sprague-Dawley rats (7-week-old) were placed on a standard diet (PFC ratio = 21:16:63), LCT-containing ketgenic diet (LKD, PFC ratio = 12:87:1) or MCT-containing ketogenic diet (MKD, PFC ratio = 16:66:18) for 8 wks. Half the rats in each group performed 2-h swimming exercise, 5 days a week for 8 wks. After the 8-wk intervention, protein expressions of 3-oxoacid CoA transferase 1 (OXCT, a ketolytic enzyme) and PDK4 in epitrochlearis muscle were measured.
Results:
Despite the lower lipid content in the diet, plasma βhydroxybutyrate concentration in the MKD-fed rats increased to a level similar to that attained in the rats fed the LKD (85±7 vs. 83±8 mmol/L·day, p=0.99). Endurance training significantly increased OXCT protein content in epitrochlearis muscle and moreover, intake of the MKD additively enhanced the endurance training-induced increase in OXCT protein content. PDK4 protein level in skeletal muscle was substantially increased after the LKD consumption. However, such increase in the PDK4 was not observed in the MKD-fed rats regardless of endurance training status.
Conclusion:
Long-term intake of ketogenic diet containing MCT may additively enhance endurance training-induced ketone bodies utilization capacity in skeletal muscle without exerting inhibitory effects on glucose metabolism.