Diet induced changes in sympatho-adrenal activity during submaximal exercise in relation to substrate utilization in man

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Abstract
To study how the diet may influence sympatho-adrenal activity during exercise, 7 subjects were examined at rest and during submaximal exercise (25 min at 65% of .ovrhdot.VO2 max) on 2 occasions. The 1st occasion was preceded by 5 days on a carbohydrate poor diet (5% carbohydrate, 72% fat and 23% protein) and the 2nd one by 5 days on a carbohydrate rich diet (78% carbohydrate, 8% fat and 14% protein) with the same energy content. O2 uptake, respiratory exchange ratio (R), heart rate and arterial plasma concentrations of adrenaline [epinephrine], noradrenaline [norepinephrine, NE], dopamine, insulin, glucose, lactate, free fatty acids (FFA), glycerol and .beta.-hydroxybutyrate were measured at rest and during exercise. O2 uptake and heart rate during exercise were higher and R was lower after the carbohydrate poor than after the carbohydrate rich diet. During exercise the arterial plasma concentrations of FFA, glycerol and .beta.-hydroxybutyrate were higher after the carbohydrate poor than after the carbohydrate rich diet whereas concentrations of insulin and lactate were lower. At rest arterial plasma NE and adrenaline levels were similar on the 2 diets (0.70 .+-. 0.31 nM NE and 0.35 .+-. 0.32 nM adrenaline on the carbohydrate rich diet, mean values .+-. SD). Exercise induced increases in NE were more pronounced after the carbohydrate poor than after the carbohydrate rich diet (12.42 .+-. 3.41 vs. 7.45 .+-. 2.68 at 25 min of exercise, P < 0.001). A similar, although more variable, accentuation of exercise-induced increases in adrenaline was found. When compared to a carbohydrate rich diet, a carbohydrate poor diet apparently increases the relative contribution of fat to oxidative metabolism and increases the sympatho-adrenal response to exercise. Stimulation of lipolysis by sympatho-adrenal mechanisms might be of importance for the substrate availability when carbohydrate intake is low.