LAUSR

Introduction There have been many meta-analyses of randomised controlled trials on the influence of different diets on obesity-related anthropometric characteristics in adults. However, whether diet interventions can effectively decrease obesity-related anthropometric characteristics remains unclear. The objective of this study is to summarise and synthesise the evidence on the effects of diet on obesity-related anthropometric characteristics in adults by an umbrella review of meta-analyses of randomised controlled trials. Methods and analysis We will first retrieve English articles only published before 15 December 2021 by searching PubMed, Embase and Web of Science. Only articles that are meta-analyses of randomised controlled trials will be included. Three researchers will independently screen the titles and abstracts of retrieved articles and check the data extracted from each eligible meta-analysis. In each meta-analysis, we will consider calculating the effect size of the mean difference of the effect of each diet on obesity-related anthropometric characteristics in adults using a random-effect model or a fixed-effect model according to heterogeneity. Study heterogeneity (Cochrane’s Q and I2 statistics) and small-study effects (Egger’s test or Begg’s test) will be considered. Evidence of each effect size will be graded according to the NutriGrade scoring system. We will use AMSTAR-2 (A Measurement Tool to Assess Systematic Reviews V.2) to assess the methodological quality of each meta-analysis. Ethics and dissemination This umbrella review will provide information on the effects of different diets on obesity-related anthropometric characteristics in adults. Ethical approval is not necessary for this study. We will publish the completed umbrella review and related data online. PROSPERO registration number CRD42021232826.