Abstract
Malnutrition is a typical consequence of a disturbed energy balance. The intake of energy substrates should meet the requirements of organism and reflect the ability to metabolize the received substrates in various clinical situations. That means that required energy intake is dependent not only on energy expenditure (measured as substrate oxidation during indirect calorimetry) but also on requirements of organism for growth, defense against infection, healing process, regeneration, and so on. Many malnourished patients experience a combination of stress and underfeeding. Both nutritional status and disease activity must be considered when nutritional support is required; this information is important for selection of energy substrates and prediction of suitable energy balance. Therefore, proper knowledge of energy metabolism principles is important as well as information about methods of energy expenditure measurement. During an acute catabolic phase, the energy balance should be neutral, because efficient anabolic reaction is not possible. However, after the acute condition has subsided, the undernourished subject should be in positive energy balance with the goal to ensure the restoration of original “healthy” condition. The period of positive energy balance should be long enough and combined with rehabilitation therapy and increased protein intake.