The effects of beetroot and nitrate supplementation on body composition: a GRADE-assessed systematic review and meta-analysis

This systematic review and meta-analysis aimed to investigate the effects of beetroot (BR) or nitrate supplements on body composition indices. A systematic search was conducted for randomised controlled trials (RCT) published up to August 2022 among online databases including Scopus, PubMed/Medline, Web of Science and Embase. Meta-analyses were carried out using a random-effects model. The I-2 index was used to assess the heterogeneity of RCT. A total of twelve RCT met the inclusion criteria for this meta-analysis. The pooled effect size of included studies indicated that BR or nitrate supplementation did not change body weight (weighted mean differences (WMD): -0 center dot 14 kg, 95 % CI -1 center dot 22, 1 center dot 51; P = 0 center dot 836; I-2 = 0 %), BMI (WMD: -0 center dot 07 kg/m(2), 95 % CI -0 center dot 19,0 center dot 03; P = 0 center dot 174, I-2 = 0 %), fat mass (WMD: -0 center dot 26 kg, 95 % CI -1 center dot 51, 0 center dot 98; P = 0 center dot 677, I-2 = 0 %), waist circumference (WMD: -0 center dot 28 cm, 95 % CI -2 center dot 30, 1 center dot 74; P = 0 center dot 786, I-2 = 0 %), body fat percentage (WMD: 0 center dot 18 %, 95 % CI -0 center dot 62, 0 center dot 99; P = 0 center dot 651, I-2 = 0 %), fat-free mass (WMD: 0 center dot 31 kg, 95 % CI -0 center dot 31, 1 center dot 94; P = 0 center dot 703, I-2 = 0 %) and waist-to-hip ratio (WMD: 0, 95 % CI -0 center dot 01, 0 center dot 02; P = 0 center dot 676, I-2 = 0 %). Subgroup analyses based on trial duration, BR or nitrate dose, study design, baseline BMI and athletic status (athlete v. non-athlete) demonstrated similar results. Certainty of evidence across outcomes ranged from low to moderate. This meta-analysis study suggests that BR or nitrate supplements cannot efficiently ameliorate body composition indices regardless of supplement dosage, trial duration and athletic status.