Effect of diet on the utilization of blood‐borne and intramuscular substrates during exercise in man

Abstract

Subjects [20 humans] were studied at rest and during a 25 min submaximal exercise (65% of .ovrhdot.VO2 max [maximal O2 consumption]) on 2 occasions, the 1st preceded by a fat rich diet and the 2nd by a carbohydrate rich diet. O2 uptake, respiratory exchange ratio (R) and arterial-femoral venous differences for glucose, lactate, .beta.-hydroxybutyrate and FFA [free fatty acids] (based on the fractional extraction of 3H-palmitate) were measured at rest and during exercise. Changes in intramuscular glycogen, triglyceride and lactate concentrations were determined in muscle biopsies taken before and immediately after exercise form m. [musculus] quadriceps femoris. R was lower after the fat than after the carbohydrate diet and simultaneously the FFA extraction by the exercising leg was higher. The muscle triglycerides did not change significantly during exercise after either diet. The glucose extraction was insignificantly greater after the fat diet. The glycogen reduction was numerically smaller after the fat diet, but the difference was uncertain and difficult to evaluate due to a large variation after the carbohydrate diet. However, muscle lactate accumulation and release by the exercising leg was smaller after the fat diet, indicating a slower rate of muscle glycogenolysis. A fat rich diet increases the relative contribution of fat to the oxidative metabolism. This increase is greatly covered by plasma FFA. The concomitant decrease in carbohydrate utilization concerns muscle glycogen rather than blood glucose.