Due to the characteristics of critically ill patients, elaborating recommendations on nutritional support for these patients is difficult. Usually the time of onset of nutritional support or its features are not well established, so that its application is based on experts' opinion. In the present document, recommendations formulated by the Metabolism and Nutrition Working Group of the Spanish Society of Intensive and Critical Medicine and Coronary Units (SEMICYUC) are presented. Recommendations are based on the literature analysis and further discussion by the working group members in order to define, consensually, the more relevant issues of metabolic and nutritional support of patients in a critical condition. Several clinical situations have been considered which are developed in the following articles of this publication. The present recommendations aim at providing a guideline for the less experienced clinicians when considering the metabolic and nutritional issues of critically ill patients.