Malnutrition is a critical factor in almost all pathological conditions in humans. The human body contains many 'soldiers' and mechanisms that protect it from threats, whether internal or external. Maintaining these self-defense means is dependent on healthy nutrition and regular physical activity. This book considers the intricacies of healthy nutrition, calculation of the daily nutritional needs, the balance of incoming and outgoing energy, healthy restoration of body weight disorders (overweight and underweight), and the treatment of food intolerance, as well as the use of food supplements and ergogenic aids in sport.