Effects of l-carnitine supplementation on weight loss and body composition: A systematic review and meta-analysis of 37 randomized controlled clinical trials with dose-response analysis

Abstract

Clinical evidence which investigated the effects of l-carnitine, a vitamin-like substance, on weight loss had led to inconsistent results. This study therefore aimed to examine the effect of l-carnitine supplementation on body weight and composition by including the maximum number of randomized controlled trials (RCTs) and to conduct a dose-response analysis, for the first time. Online databases were searched up to January 2019. In total, 37 RCTs (with 2292 participants) were eligible. Meta-analysis showed that l-carnitine supplementation significantly decreased body weight [Weighted mean difference (WMD)=-1.21kg, 95% confidence interval (CI):-1.73,-0.68; P<0.001], body mass index (BMI) (WMD=-0.24kg/m2, 95% CI:-0.37,-0.10; P=0.001), and fat mass (WMD=-2.08kg, 95% CI:-3.44,-0.72; P=0.003). No significant effect was seen for waist circumference (WC) and body fat percent. The meta-analysis of high-quality RCTs only confirmed the effect on body weight. A non-linear dose-response association was seen between l-carnitine supplementation and body weight reduction (P<0.001) suggesting that ingestion of 2000mg l-carnitine per day provides the maximum effect in adults. This association was not seen for BMI, WC and body fat percent. l-carnitine supplementation provides a modest reducing effect on body weight, BMI and fat mass, especially among adults with overweight/obesity.