Effects of Ramadan fasting on substrate oxidation, physiological and perceptual responses during submaximal intensity running in active men

This study examines the effects of Ramadan fasting on various psycho-physiological measures during submaximal exercise, under real-world ecologically valid conditions. Eleven Muslim men performed a 30-min continuous running on a treadmill at intensity 65 % VO_2max in the Ramadan fasted (RAM) and non-fasted (or Control, CON) state, on two separate occasions in a crossover and counter-balanced order. The amount of calories and fluid volume intake of participants’ last pre-exercise main meal, i.e., ~3–4 h prior to CON and ~10–12 h prior to RAM trial, were standardized. To simulate real world scenario, their 24 h pre-trial sleep hours and pattern were typical of the Ramadan and non-Ramadan period. There was no significant difference in total training load for the week prior to the RAM and CON exercise trials. Results showed no differences between RAM and CON trial for both carbohydrate and fat oxidation rate (both p > 0.05; effects size (d) = small and trivial, respectively). Blood glucose in RAM trial was lower at pre-exercise and higher at post-exercise than CON trial (both p < 0.05; d = moderate). Daytime sleepiness and moods state showed no differences between conditions (all p > 0.05; d = trivial). Heart rate throughout run (p = 0.03) and ratings of perceived exertion (p = 0.03, d = small) were higher in RAM. In conclusion, Ramadan fasting has no major impact on substrate utilization and is not an effective ‘fat-burning’ enhancing activity to lose fat mass. Running in the Ramadan fasted state led to a greater psycho-physiological stress compared to the same run in the non-fasted state.