Impact of Dietary Protein Quantity and Macronutrients Composition on Body Composition: A Systematic Review, Pairwise, and Network Meta-Analysis

Objectives: A systematic review and both pairwise and network meta-analysis was conducted to investigate the impact of dietary protein quantity and macronutrients composition on body composition from complied data of randomized controlled trials. Methods: Four databases including PubMed, Embase, CINAHL and Web of Science were searched and a total of 83 articles published between 2003 and 2023 were included. Based on different macronutrients compositions in diets, we further divided into 6 groups; high-protein, high-carbohydrates and high-fat (HHH), high-protein, high-carbohydrate and low-fat (HHL), high-protein, low-carbohydrate and high-fat (HLH), normal-protein, high-carbohydrates and high-fat (NHH), normal-protein, high-carbohydrates and low-fat (NHH) and normal-protein, low-carbohydrates and high-fat (NLH) diets. Results: In the pairwise meta-analysis, high-protein diets (HPD) showed significant favorable effects on body weight (standardized mean difference [SMD) = -0.25; 95% CI: -0.40, -0.11), body mass index (BMI) (SMD = -0.26; 95% CI: -0.40, -0.11), waist circumference (WC) (SMD = -0.19; 95% CI: -0.33, -0.04), fat mass (FM) (mean difference [MD] = -0.64 kg; 95% CI: -0.98, -0.29) and lean body mass (LBM) (MD = 0.34 kg; 95% CI: 0.11, 0.57) compared with normal-protein diets (NPD). In network meta-analysis, all HPD groups, even with different macronutrients compositions, generated higher SUCRA scores than NPD. However, among HPD groups, different macronutrients compositions resulted in distinct ranking scores for specific outcomes. HHH secured the top ranking for reducing body weight (SUCRA: 41.8%), BMI (SUCRA: 53.2%), WC (SUCRA: 80.3%), and FM (SUCRA: 42.6%). While HHL diets was ranked best for reducing hip circumference (SUCRA: 42.5%) and increasing LBM (SUCRA: 46.1%); HLH diets generated the best rank in reducing body fat% (SUCRA: 93.3%). Conclusions: This study revealed a benefit of HPD consumption on body composition however, manipulating other macronutrients also matters when consuming HPD for body composition management. Funding Sources: National University of Singapore.