Competitive sport and strenuous physical activity make demands on our body above the usual physiological range. Measurable muscle damage and accumulation of metabolic products cause pain and other effects that can be demonstrated. From the medical point of view we have to provide athletes with adequate nutrients and energy for the maintenance of homeostasis and to cover their higher energetic and nutritional needs as compared to sedentary people. Some athletes may need supplements to replace essential nutrients missing from their regular (especially if unbalanced) diet, or to restore special needs, such as fluids and salts, while exercising in extreme climatic conditions. Overload of additives is frequent in both professional and amateur athletes. Very often, the proposed mechanism for the rationale of using these additives, 'supplements' or 'ergogenic compounds', is related to their possible effect on the endocrine-metabolic system, in many cases without solid evidence-based research. Yet it needs to be remembered that there is still disagreement on what are the required physiological needs of athletes for amino acids and other supplements. Different surveys on the use of supplements report that 40-60% of athletes take food additives, and the numbers are rapidly increasing. A more alarming fact is that about 50% of the recommendations to use these supplements come from non-professional people. Since some additives may change the endocrine and metabolic homeostasis in an unexpected way--as an extreme example of close to 50 deaths reported from the use of L-tryptophan supplements--it is important to study carefully the effects of additives given to athletes, and to increase awareness of the lack of knowledge in this field.