Mitochondrial Density in Muscle is Key Determinant of Metabolic Flexibility

If you happened to have listened to Carl Lenore's interview with Mike T Nelson's on SuperHumanRadio, last week, you will be familiar with the concept of metabolic flexibility and how important it is for your body to be able to adapt quickly to varying energy demands and sources. A recent study by scientists from the Pittsburgh School of Medicine (Chomentowski. 2010) had a similar background. Along with several markers of metabolic flexibility the group measured intermyofibrillar and subsarcolemmal (SS) mitochondrial content in a sample of forty sedentary adults with a wide spectrum of insulin sensitivity (insulin-sensitive lean subjects, insulin-resistant nondiabetic subjects, and subjects with type 2 diabetes mellitus).

Intermyofibrillar mitochondrial content was lower in the insulin-resistant nondiabetic subjects and type 2 diabetes mellitus groups, significantly correlating with glucose disposal in both men (R = 0.72, P < 0.01) and women (R = 0.53, P < 0.01). In contrast, SS mitochondrial content was similar among groups. Lower intermyofibrillar mitochondrial content was not explained by mitochondrial size, altered fiber-type distribution, or differences in maximum aerobic capacity. Intermyofibrillar mitochondrial content was significantly correlated with fasting respiratory quotient (R = -0.46, P = 0.003) and metabolic flexibility (R = 0.38, P = 0.02).

The correlation between low intermyofibriallar mitochondrial content and insulin-resistance the researchers found seems to substantiate the longstanding recommendation to exercise and build muscle or make existing muscle work more effectively to prevent and treat diabetes and the metabolic syndrome. However, dietary factors and genetics may as well be important factors influencing mitochondrial density.