The effect of Capsaicinoids or Capsinoids in red pepper on thermogenesis in healthy adults: A systematic review and meta-analysis

The outcomes of the earlier trials are controversial concerning the effect of Capsaicinoids/Capsinoids on thermogenesis. We carried out this systematic review and meta-analysis to examine the effect of Capsaicinoids/Capsinoids on thermogenesis indices including resting metabolic rate (RMR) and respiratory quotient (RQ) in healthy adults. An electronic literature search was conducted between 1990 and 2019, using the following databases: PubMed, Web of Sciences, Scopus, Cochrane Central Register of Controlled Trials, and EMBASE. Placebo-controlled clinical trials were considered as eligible papers. Effect sizes were pooled using weighted mean difference (WMD), with a random-effects model. Of the 4,092 articles, 13 studies were included in the meta-analysis. Pooled effect sizes revealed that compared with placebo, Capsaicinoids/Capsinoids significantly increased RMR (WMD: 33.99 Kcal/day, 95% CI: 15.95, 52.03;I-2: 0%,p= .94), energy expenditure, and fat oxidation. It also significantly lessened RQ (WMD: -0.01, 95% CI: -0.02, -0.01;I-2: 5.4%,p= .39) and carbohydrate oxidation. Moreover, intervention in capsule form for longer duration had a more considerable influence on RMR than comparative groups. We observed moderate improvement in RMR, RQ, and fat oxidation following supplementation with Capsaicinoids/Capsinoids. However, further high-quality studies are required to clarify the thermogenic properties of Capsaicinoids/Capsinoids.