Effect of Ramadan fasting on fuel oxidation during exercise in trained male rugby players

Purpose: The aim of this study was to assess the effect of Ramadan fasting on substrate oxidation in trained athletes during moderate-intensity exercise, Methods: Nine trained men (age: 19 +/- 2 yr, Height: 1.78 +/- 0.74 m) were tested on three occasions: during a control period immediately before Ramadan (C), at the end of the first week (Beg-R), and during the fourth week of Ramadan (End-R). On each occasion, they performed submaximal cycle ergometer exercise, with work-rates that were increased progressively (loadings corresponding to 20, 30, 40, 50, 60% of Wmax). Steady-state substrate oxidation was evaluated by indirect calorimetry. Results: Participants showed significant decreases in body mass and body fat at the end of Ramadan, relative to initial control values (P < 0.001). The daily food intake was also reduced during Ramadan (P < 0.01). Haemoglobin concentrations and hematocrit were significantly higher at the end-Ramadan, both at rest (P < 0.001 and P < 0.0001 respectively) and after exercise, (P < 0.05 and P < 0.01 respectively) compared to control measurements made before Ramadan. At the end of Ramadan, our subjects had increased their fat utilization during exercise. The cross-over was observed at a higher intensity at the End-R (35% vs. 30% of Wmax, P < 0.001). For the same power output, the Lipox max was also higher at the End-R, compared to control value (265 +/- 38 vs. 199.1 +/- 20 mg/min, P < 0.001). Conclusion: Ramadan fasting increases the lipid oxidation of trained athletes during submaximal exercise. The increased fat utilisation may be related to decreases in body mass and body fat content.