The intermittent fasting of Ramadan could affect various aspects of body physiology and biochemistry important to athletic success. Sleep time may be shortened. Disturbance of psychomotor performance, impaired vigilance and slower reactions can be observed particularly during afternoon. Food intake is limited to night-time meals. Well disciplined athletes usually maintain energy balance unless daily energy expenditures are very high. Daytime fluid depletion is inevitable if athletes exercise in the heat.