Data extraction and quality assessment

The information and data in all eligible studies were extracted: basic characteristics of each study (first author, publication year, country, sample size, age of the participants), study design (elements in immunonutrition formula, nutritional support duration, approach of the nutritional support), and outcomes of interest (clinical outcomes, immune and biochemical indices).

The quality of included investigations was assessed according to the Cochrane Collaboration tool published in the Cochrane Handbook for Systematic Reviews of Interventions (Version 5.1.0). “Risk of bias” consisting chiefly of six domains: random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and other bias. Each domain was graded as “low risk of bias,” “high risk of bias,” or “risk of bias unclear.”