Effect of exercise interventions on brain-derived neurotrophic factor expression in people with overweight and obesity: protocol for a systematic review and meta-analysis.

INTRODUCTION: Epidemic obesity ('globobesity') has led to a considerable rise in the prevalence and incidence of many disabling conditions, including cognitive dysfunction. Recent evidence has suggested that habitual exercise can alleviate the deleterious effects of obesity on cognitive functioning across the lifespan. Given that there is a potential link among obesity, exercise, cognitive health and brain-derived neurotrophic factor (BDNF), this systematic review aims to critically appraise interventional trials on exercise and BDNF and to estimate the pooled effect of exercise training on BDNF levels among healthy individuals with overweight and obesity. METHODS AND ANALYSIS: Six electronic databases-PubMed, MEDLINE, EMBASE, Web of Science, Ovid Nursing Database and SPORTDiscus-will be searched from their inception through December 2022. Only interventional studies, including randomised controlled trials and quasi-experimental studies, with full text available and reported in English will be included. The primary outcomes will be changes in BDNF levels among healthy subjects with overweight and obesity following either acute or chronic bouts of exercise interventions. Two reviewers will independently conduct data extraction and risk of bias assessment for included trials using the Physiotherapy Evidence Database Scale. We will produce a narrative synthesis, with findings categorised by sex, age groups and types of exercise training. Data will be extracted and pooled for meta-analyses using random-effects models. ETHICS AND DISSEMINATION: No formal ethical approval is required for this systematic review. The findings of this review will be disseminated through peer-reviewed publications. PROSPERO REGISTRATION NUMBER: CRD42023414868.