The effect of body weight changes and endurance training on 24 h substrateoxidation

OBJECTIVE: To investigate the effect of exercise training and dietary macro nutrient composition on 24 h substrate oxidation in male, obese subjects. DESIGN: A 16 month exercise intervention study was executed, including a we ight loss period with a very low energy diet (VLED) for 2 months at the sta rt of the study. SUBJECTS: Twelve male, obese subjects (age 36.3+/-5.1 y; body weight 94.6+/ -13.9 kg; body mass index, BMI 30.8+/-3.0 kg/m(2)) and in an additional stu dy 15 lean, well-trained subjects (age 36.2+/-7.2 y ; body weight 72.2+/-5. 9 kg; BMI 22.3+/-1.7 kg/m2) participated. MEASUREMENTS: Substrate oxidation was measured during a standardized 36 h s tay in the respiration chamber at the start of the study (0 months), and at 4, 10 and 16 months. In the respiration chamber subjects were randomly ass igned to a high-fat (Hi.F) diet (60% of energy (En%) fat) or a reduced-fat (Red.F) diet (30 En% fat). The well-trained group was measured once in the respiration chamber for 36 h according to the same protocol. RESULTS: At any time point, independent of the diet consumed, the 24 h carb ohydrate (CHO) balances in the chamber were mostly negative (means ranging from +31 to -98 g/d) and the fat balances mostly positive (means ranging fr om -26 to +38 g/d) for the obese a well as for the lean, well-trained group . For both diets an increased shortage of 70 g of CHO was found at 16 month s compared with 4 months, and an increase in fat balance of 33 g during the same time period in the obese subjects, indicating that CHO oxidation had increased with 12 months endurance training. In the well-trained group the 24 h CHO balance was even more negative for both types of diet (-103 to -18 5 g/d for the Red.F and Hi.F diet, respectively) under similar conditions c ompared with the trained obese group. CONCLUSION: The changes in 24 h substrate utilization in the obese, as well as in the well-trained group, suggest that endurance training increased th e reliance on carbohydrate oxidation and therefore did not increase 24 fat oxidation.