Conceptualization and Measurement of 24 hr Timing of Eating and Energy Intake: A Systematic Review of Chronic Disease Literature

OBJECTIVES: Beyond diet quality, the timing of eating and energy intake within the 24 hr day (24 hr TOE) may have important implications for chronic disease risk, and research in this area (i.e., chrononutrition) is rapidly growing. The 2020 Dietary Guidelines Advisory Committee recommended the development of consistent terminology to address the lack of TOE standardization. This systematic review summarizes the current conceptualization and measurement of 24 hr TOE in the chronic disease literature. METHODS: This review is registered on PROSPERO (CRD42021236621). The initial search was conducted in September 2021 in PubMed/MEDLINE, Embase, CINAHL Plus, and Scopus. The search was limited to English-language, full-text, peer-reviewed, original literature reporting results from adults from 2000 to present. Studies were eligible if they reported an association between a 24 hr TOE variable and obesity, cardiovascular disease, diabetes, cancer, or related clinical risk factors. Qualitative synthesis will compare 24 hr TOE conceptualization, measurement, and variables across all studies and differences by study features (e.g., design, disease context). RESULTS: Of the 6879 articles included in title and abstract screening, 706 are being assessed for full-text eligibility, and as of February 2022, n = 140 articles are eligible for inclusion in the qualitative synthesis. Most studies included to date are in an obesity-specific context. Studies use 24 hr dietary recalls, food records, and various meal timing surveys to measure 24 hr TOE. 24 hr TOE variables operationalize inter-related aspects of time and energy intake in varying ways. Common variable types include: 1) timepoint (specific time to represent when intake occurs, such as ‘breakfast time’); 2) duration/interval (length of time or interval when intake does/does not occur, such as ‘eating window’); and 3) distribution (proportion of daily intake at a given time interval, such as ‘% of energy before noon’). Operationalization of 24 hr TOE variables varied widely across studies, particularly between intervention and observational designs. CONCLUSIONS: The wide range of 24 hr TOE variables suggests a need for standardization to guide future research in chrononutrition and to facilitate cross-study comparison. FUNDING SOURCES: BMB was supported by 5T32CA250803-02. There are no other funding sources to report.