Effects of low-carbohydrate diet on thermoregulatory responses to graded exercise in men

The aim of this study was to investigate the effects of a low-carbohydrate diet on temperature regulation in men performing an exercise of increasing intensity on a bicycle ergometer under thermoneutral conditions (ambient temperature of 23 degreesC and relative air humidity of 52-60%). Seven male subjects were tested after a control (C: 60% carbohydrates, 20% proteins and 20% fat) and a low-carbohydrate (LCHO: 50% fat, 45% proteins and 5% carbohydrates) diet. Blood lactate (LA), heart rate (HR), oxygen uptake ((V)over dotO(2)) minute ventilation (V-E), beta -hydroxybutyrate acid (beta -HB), tympanic (T-ty) and mean skin (T-sk) temperatures as well as electrical skin resistance (ESR) were measured. On the basis of ESR, dynamics of sweating was estimated. The level of P-HB was 1.92 mM after LCHO and 0.28 mM after C diet (P<0.001). The maximum LA concentrations were 7.9 and 9.3 mM (P<0.05), respectively. Increases in T-ty were similar (1.4 and 1.2 degreesC) after both diets. Delay time for sweating was shorter after LCHO in comparison with C diet (9.4 vs 12.1 min, P<0.05), but the temperature threshold for this reaction was unchanged (37.05 vs 36.95<degrees>C). It can be concluded that the low-carbohydrate diet modifies thermoregulatory and metabolic responses to exercise-in men. Some non-thermal diet-related factors probably attenuate the heat dissipation mechanism during graded exercise in man.