Experimental and Outcome‐Based Approaches to Protein Requirements in the Intensive Care Unit

Abstract

Insight into protein requirements of intensive care unit (ICU) patients is urgently needed, but at present, it is unrealistic to define protein requirements for different diagnostic groups of critical illness or at different stages of illness. No large randomized controlled trials have randomized protein delivery, adequately addressed energy intake, and evaluated relevant clinical outcomes. As a pragmatic approach, experimental studies have focused on protein requirements of heterogeneous ICU patients. Data are scarce and the absolute value of protein requirements therefore is an approximation. Experimental studies indicate a protein requirement of >1.2 g/kg protein, which is supported by several outcome-based observational studies. Protein intake levels of up to 2.0-2.5 g/kg appear to be safe. A higher level of personalized treatment, within 1.2 and 2.5 g/kg, must involve identification of patients with low muscle protein mass that might benefit most from adequate protein nutrition in the ICU.

Association of Energy and Protein Delivery on Skeletal Muscle Mass Changes in Critically Ill Adults: A Systematic Review

“…Delivery of energy above and below an individual's needs may be detrimental to muscle mass. Specifically, caloric restriction can lead to protein‐energy malnutrition and muscle wasting, while overfeeding energy may decrease capillary blood flow and amino acid transfer to muscle tissue via perivascular adipose tissue . The majority of participants in this review received appropriate energy provision for the acute stages of critical illness compared with measured needs or clinical guidelines .…”

Current perspective for tube feeding in the elderly: from identifying malnutrition to providing of enteral nutrition

“… 77 The basis for the protein dose recommendation includes a number of studies with nitrogen balance as the outcome. 79 As an example, Ishibashi et al 80 tested three protein intake levels (1.1, 1.5, and 1.9 g/kg of FFM) and found that a median protein intake of 1.5 g/kg/FFM or 1.2 g/kg or actual body weight was associated with the lowest body protein loss. Similarly, multiple observational studies have suggested that a protein target of >1.2 g/kg of body weight was associated with lower mortality, even when independent of caloric goal.…”

Protein in the Hospital: Gaining Perspective and Moving Forward

“…Consideration should also be placed on N balance interpretation when providing insight to inform protein provision. For instance, are clinical outcomes similarly affected with an N balance of −17 g/d improving to −12 g/d compared with −7 g/d improving to −2 g/d, or is there a certain N balance threshold that needs to be met to prove beneficial?…”

“…Although flaws in current protein dosing guidelines are easily identified, it is difficult to propose new recommendations capable of maintaining muscle mass because of the complexity of an individual's response to protein intake. Many factors are capable of altering the body's ability to convert dietary protein into cellular protein, including protein quality (ie, dietary protein amino acid composition and digestibility), digestion rate, nonprotein energy intake, anabolic resistance, muscle disuse, timing of ingestion, and inflammatory status . The sum of these factors make defining protein requirements for a clinical population very difficult.…”

“…Although not discussed in detail, anabolic resistance, immobility, timing of ingestion, route of ingestion, and inflammatory status are crucial elements that shape protein requirements . Individual variations in any of these variables may cause substantial differences in amino acid and protein needs, even among individuals of similar disease states.…”