BackgroundCircadian rhythm, the body's internal clock, synchronises with the 24-h light-dark cycle and is influenced by environmental cues such as light exposure and meal timing. Disruptions in this rhythm due to modern lifestyle factors, including irregular eating schedules, are linked to increased risks of cardiometabolic diseases. Time-restricted eating (TRE), which limits food intake to an 8-12 h window, often aligns with daytime (diurnal) eating and supports circadian alignment. In contrast, nocturnal TRE patterns, such as during Ramadan, may disrupt this rhythm by shifting food intake to nighttime.AimTo conduct a systematic review and meta-analysis evaluating the differential impacts of diurnal and nocturnal TRE on cardiometabolic health and circadian rhythm in healthy adults.MethodsThis review follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and is registered with PROSPERO (CRD42023374947). A comprehensive search will be conducted using PubMed, Web of Science and Scopus. Two independent reviewers will screen titles, abstracts and full texts, extract data using a standardized form and assess risk of bias. Qualitative and quantitative (meta-analysis) synthesis will be conducted where appropriate.SummaryThis protocol outlines the methodology for synthesising current evidence on the differential effects of diurnal versus nocturnal TRE patterns. The findings will inform future dietary interventions aimed at optimising cardiometabolic health through circadian-aligned nutrition strategies.
