Impact of Reduced Carbohydrate Intake after Exercise on Breath Acetone Levels

Abstract

PURPOSE: The purpose of the present study was to deter determine the impact of reduced carbohydrate (CHO) intake after sprint exercise on breath acetone levels during post-exercise. METHODS: Nine subjects (20.8 ± 0.2 yrs, 170.1 ± 1.6 cm, 65.1 ± 1.8 kg) conducted two trials, consisting lower CHO trial (LOW) or normal CHO trial (NOR). In each trial, the subjects came to the laboratory at 7:30 to evaluate breath acetone level, blood variables and resting metabolic rate. From 17:00, they started repeated sprint exercise (4 × 30 s maximal cycle sprint exercise). After exercise, isoenergetic meals (during 2-3 h after exercise) were provided with containing normal CHO (60% for CHO, 20% for protein, 20% for fat) for NOR or reduced CHO (20% for CHO, 20% for protein, 60% for fat) for LOW. Time course changes in breath acetone levels were monitored immediately before exercise, immediately after exercise, 1 h, 3h, 4h and on the following morning. RESULTS: In the LOW, exercise markedly increased breath acetone levels during post-exercise (trial × time interaction: p<0.05). At 4 h after exercise, breath acetone level was significantly higher in LOW (0.9 ± 0.02 ppm) than in NOR (0.66 ± 0.07 ppm, p < 0.05). However, a significant difference between the trials was not observed on the following morning. Respiratory exchange ratio (RER) on the following morning was significantly lower in the LOW (0.81 ± 0.02) than in the NOR (0.87 ± 0.02, p < 0.05). Moreover, LOW showed significantly lower contribution of CHO oxidation (34 ± 4.8 %) than that in NOR (50 ± 6.2 %, p < 0.05), whereas fat oxidation was significantly higher in LOW (66 ± 4.8 %) than in NOR (50 ± 6.2 %, p < 0.05). CONCLUSIONS: Reduced CHO intake after exercise increased breath acetone level during early phase of post-exercise (4 h after exercise), suggesting augmented fat metabolism in the liver under impaired CHO availability. However, the increased breath acetone level by reduced CHO intake was not evident on the following morning. The results may suggest that breath acetone levels can be available to evaluate CHO availability following intensive exercise.