The Effects of Protein Nutrition on Muscle Function in Critical Illness: A Systematic Review and Meta-Analysis

Background: owing to altered protein metabolism during critical illness, skeletal muscles are utilised as a source of protein, with subsequent debilitating effects on both muscle structure and function. Protein nutrition has been shown to improve clinical outcomes in critically unwell patients; however, the impact on muscle function is less established. Therefore, the aim of this review was to systematically determine the effect of protein dose on skeletal muscle strength in critically ill patients. Methods: we searched five databases (Ovid MEDLINE, Embase, Emcare, CINAHL, and PubMed) and clinical trial registers for randomised controlled trials (RCTs) of non-pregnant, adult patients admitted to an intensive care unit (ICU), which assessed the impact of different doses of protein nutrition on muscle strength. Studies investigating only muscle structure or with co-interventions were excluded. Six RCTs were eligible for inclusion, and five were suitable for meta-analysis. Results: there was a significant difference in skeletal muscle strength with higher versus lower protein intakes, with a mean difference of 2.36 kg (95% CI: 0.37–4.35). The mean difference in protein dose was 0.46 g/kg/d (95% CI: 0.29–0.64). Inconsistency was evident across the included studies, with risk of bias ranging from moderate to high. Conclusion: muscle strength of ICU patients does appear to be affected by different protein doses. However, trials focusing on muscle function are limited by number and quality, highlighting a clear need for future work.