Protein Requirements in Critical Illness: Do We Really Know Why to Give So Much?

The protein and energy requirements of critically ill patients treated in intensive care units (ICUs) have been actively discussed recently. Currently published clinical recommendations and reviews suggest significant increases of protein provision to 2-2.5 g/kg/d in some populations of ICU patients. However, a detailed analysis of the main sources of these recommendations reveals a number of serious contradictions, as well as an absence of obvious evidence supporting the allotment of high doses of protein. We went through these recommendations and reviewed cited articles and other studies, and we have separated our arguments against excessive protein provision into sections.

Protein Kinetics and Metabolic Effects Related to Disease States in the Intensive Care Unit

Evaluating protein kinetics in the critically ill population remains a very difficult task. Heterogeneity in the intensive care unit (ICU) population and wide spectrum of disease processes creates complexity in assessing protein kinetics. Traditionally, protein has been delivered in the context of total energy. Focus on energy delivery has recently come into question, as the importance of supplemental protein in patient outcomes has been shown in several recent trials. The ICU patient is prone to catabolism, immobilization, and impaired immunity, which is a perfect storm for massive loss of lean body tissue with a unidirectional flow of amino acids from muscle to immune tissue for immunoglobulin production, as well as liver for gluconeogenesis and acute phase protein synthesis. The understanding of protein metabolism in the ICU has been recently expanded with the discovery of how the mammalian target of rapamycin complex 1 is regulated. The concept of "anabolic resistance" and identifying the quantity of protein required to overcome this resistance is gaining support among critical care nutrition circles. It appears that a minimum of at least 1.2 g/kg/d with levels up to 2.0 g/kg/d of protein or amino acids appears safe for delivery in the ICU setting and may yield a better clinical outcome.