Effects of supplementation with carnosine and other histidine-containing dipeptides on chronic disease risk factors and outcomes: protocol for a systematic review of randomised controlled trials

INTRODUCTION: Ageing of populations globally, coupled with the obesity epidemic, has resulted in the rising prevalence of chronic diseases including diabetes, cardiovascular diseases, cancers and neurodegenerative disorders. Prevention of risk factors that contribute to these diseases is key in managing the global burden of chronic diseases. Recent studies suggest that carnosine, a dipeptide with anti-inflammatory, antioxidative and antiglycating properties may have a role in the prevention of chronic diseases; however, no previous reviews have examined the effects of carnosine and other histidine-containing peptides (HCDs) on chronic disease risk factors and outcomes. We aim to conduct a comprehensive systematic review to examine the effects of supplementation with carnosine and other HCDs on chronic disease risk factors and outcomes and to identify relevant knowledge gaps. METHODS AND ANALYSIS: Electronic databases including Medline, Cumulative Index of Nursing and Allied Health, Embase and all Evidence-Based Medicine will be systematically searched to identify randomised controlled trials (RCTs) and systematic reviews of RCTs, comparing supplementation with carnosine and/or other HCDs versus placebo, usual care or other pharmacological or non-pharmacological interventions. One reviewer will screen titles and abstracts for eligibility according to prespecified inclusion criteria, after which two independent reviewers will perform data extraction and quality appraisal. Meta-analyses, metaregression and subgroup analyses will be conducted where appropriate. ETHICS AND DISSEMINATION: Ethics approval is not required as this review does not involve primary data collection. This review will generate level-one evidence regarding the effects of carnosine supplementation on chronic disease risk factors and outcomes and will be disseminated through peer-reviewed publications and at conference meetings to inform future research on the efficacy of carnosine supplementation for the prevention of chronic diseases. PROSPERO REGISTRATION NUMBER: CRD42017075354.