**Review Title** Impact of the first COVID-19 lockdown on body weight: A combined systematic review with a meta-analysis **Review question** Did body weight of people change during the first COVID-19 lockdown? **Searches** PubMed®, Scopus®, Web of Science® and Embase® databases will be used for all searches. A basic search strategy will be developed for PubMed according to the follow search string: “((BMI) OR (Weight change) OR (Weight gain) OR (weight loss)) AND (COVID-19)” and modified accordingly for other research engines. **Types of study to be included** We will include observational studies (Prospective and retrospective cohort studies and Cross-sectional studies) **Condition or domain being studied** During the Covid-19 pandemic strickt measures of confinement were enforced by the governments of several countries in order to prevent the transmission of the virus. In this study we will investigate the impact of the first COVID-19 lockdown on body weight. **Participants/population** **Inclusion criteria**: Healthy subjects or subjects with asymptomatic Covid-19 infection >16 years old. **Exclusion criteria**: • Hospitalized patients • Covid-19 patients • Patients with Chronic diseases which affect body weight • Age <16 years old **Intervention(s), exposure(s)** Covid-19 first lockdown (March-May 2020) **Comparator(s)/control** Body weight and/or BMI before the COVID-19 lockdown period **Context Main outcome(s)** Potential changes on body weight and on BMI. Timing and effect measures Not applicable. **Data extraction (selection and coding)** Our systematic review will be performed in accordance with the meta-analyses Of Observational Studies in Epidemiology (MOOSE) statement (Meta-analysis of Observational Studies in Epidemiology. A Proposal for Reporting. JAMA. 2000;283(15):2008-2012. doi: 10.1001/jama.283.15.2008.). Two reviewers will independently extract data regarding changes of body weight after the lockdown period. Any disagreement will be resolved by consensus. Authors will be contacted in order to obtain any missing data relevant to the analysis. **Risk of bias (quality) assessment** The quality of the eligible studies will be evaluated using a version of the Newcastle-Ottawa quality assessment scale for case-control and cohort studies and the modified Newcastle Ottawa scale for cross-sectional studies (Wells, G. A, Shea, B., O'Connel, D. et al. The Newcastle-Ottawa scale (NOS) for assessing the quality of non-randomized studies in meta-analyses 2013 http://www.ohri.ca/programs/clinical_epidemiology/oxford.asp). A sensitivity analysis will be performed excluding studies with low quality. **Strategy for data synthesis** • Random effects or fixed-effects models will be used and the inverse variance method. We will report effect sizes as mean differences (MD) and their 95% confidence intervals (CI). • Text and tables will be used to provide an explanation of study characteristics and findings • Table will be used to provide relevant information in regard to body weight and BMI changes (increase/decrease/no-change) **Analysis of subgroups or subsets** Different group of people (e.g. obese/non obese, adults/adolescents) and their body weight and/or BMI after/during lockdown will be analyzed. **Contact details for further information** Assoc. Prof. Michail Chourdakis e-mail: mhourd@gapps.auth.gr **Organizational affiliation of the review** • Aristotle University of Thessaloniki, Thessaloniki, Greece **Type and method of review** Systematic review and Meta-analysis **Anticipated or actual start date** 28 December 2020 **Anticipated completion date** 30 January 2021 **Funding sources/sponsors** None **Conflicts of interest** None **Language** English **Country** Greece **Stage of review** Review Ongoing **Subject index terms** BMI; weight change; weight gain; weight loss; COVID-19; SARS-COV-2