There are nutrients that although not contributing directly to enhancing athletes’ performance interfere in their health and particularly in some physiological aspects that might, at the end, have a profound effect in performance at a particular time. Athletes in general need more energetic nutrients than sedentary people and so, as several micronutrients interfere in the metabolism of carbohydrates, proteins and fat, it is reasonable to think that micronutrients involved in those processes are increasingly required in the exercising body (Manore and Thompson, 2000). Moreover, many authors have emphasised the role of several micronutrients for athletes’ health (for review see Coyle, 2000). It is clear that health and well-being are improved by physical activity and a well balanced diet (Coyle, 2000). Exercise elevates physiological and metabolic stress (Quiles et al., 1999) and both physical activity and diet are interrelated in the fact that optimal adaptation to the stress resulting from exercise requires a balanced diet, containing all its essential components (Suzuki et al., 1999, Coyle, 2000). The immune system is greatly affected by exercise (Nieman, 1995), several cases of immunossupression in elite athletes being related to extreme exercise (Verde et al., 1992; Nieman., 1995, Davis et al., 1997, Shephard and Shek, 1999; Gleeson and Bishop, 2000). Nutrients that have been demonstrated to contribute to a better functioning of the immune system include essential amino acids, the essential fatty acid linoleic acid, vitamin A, folic acid, vitamin B6, vitamin B12, vitamin C, vitamin E, Zn, Cu, Fe and Se. Practically all forms of immunity may be affected by deficiencies in one or more of these nutrients (Calder and Kew, 2002). Moreover, some of these nutrients have been shown to decrease due to exercise (Kobylinski et al., 1990; Quiles et al., 1998, Quiles et al., 1999). The production of energy by the mitochondria results in the formation of reactive molecular species known as free radicals, which in balanced amounts are important in several cellular mechanisms, but if over-increased, they lead to several destructive mechanisms (for review see Fehrenbach and Northoff, 2001). During the course of evolution, the antioxidant system has developed in order to prevent cell damage and to maintain equilibrium between production of free radicals and their neutralization. Many sources of stress including extreme exercise (Mastaloudis et al., 2001) increase production of free
radicals and associated reactive oxygen or nitrogen species (ROS/RNS). This is known as the oxidative stress (for review see Jenkins et al., 1984, Fehrenbach and Northoff, 2001). A good nutritional balance, which includes food products rich in antioxidant is a way to ensure adequate removal of radicals during stress and prevent cellular damages (Fehrenbach and Northoff, 2001). Among the nutrients known to have antioxidant effects are micronutrients such as the vitamins A, C and E and selenium (for review see Manore and Thompson, 2000).