Effects of Early vs. Late Time Restricted Eating vs. Daily Caloric Restriction on Weight Loss and Metabolic Outcomes in Adults with Obesity: Study Protocol for a 52-week randomized controlled trial (Preprint)

BACKGROUND Daily caloric restriction (DCR) is the most common dietary strategy used to treat obesity and reduce cardiometabolic risk. However, a substantial subset of individuals fail to achieve clinically meaningful weight loss with this strategy and instead choose to adopt alternative dietary strategies for weight loss. Time restricted eating (TRE) involves restriction of energy intake (EI) to a limited window of time each day and has been widely promoted in the media and lay press due to the idea that TRE may be easier to adhere to than DCR and/or may have greater metabolic benefit. However, there are substantial limitations in the prior research, including failure to evaluate TRE within the context of an appropriate guidelines-based behavioral support program and failure to standardize and evaluate the impact of the timing of the eating window OBJECTIVE The goal of this randomized trial is to compare the effects of early TRE (E-TRE), late TRE (L-TRE), and DCR on changes in body weight, body composition, markers of cardiometabolic health, dietary adherence, EI, physical activity and sleep. METHODS Adults with overweight or obesity (ages 18-65 years, BMI 27-45 kg/m2) who are not currently following a TRE dietary regimen (i.e., eating across less than a 10-hour period during the day) will be recruited for this study. Participants will be randomized to one of three dietary interventions delivered within a 12-month standardized behavioral weight loss program: E-TRE, L-TRE, or DCR. Participants assigned to the E-TRE group will consume all caloric intake within an 8-hour eating window from 08:00–16:00 and participants assigned to the L-TRE group will consume all caloric intake within an 8-hour eating window from 12:00–20:00. Participants assigned to the DCR group will be asked to reduce calories by ~25% from estimated weight maintenance energy requirement. All participants will receive virtual, group-based education from a registered dietitian. Outcome assessments will occur at baseline and at weeks 14, 26, and 52. The primary outcome of the study is change in body weight from baseline to week 26. Secondary outcomes include body composition, insulin sensitivity, blood pressure, glucose variability, dietary intake, meal timing, physical activity, sleep outcomes, and biologic and psychosocial measures. RESULTS This study was funded in April of 2023. Recruitment began in July of 2023 and was completed as of February 2026. Participants were recruited in 4 cohorts of 30-40 participants per cohort. Study participants in Cohort 4 are currently participating in study procedures, with data collection anticipated to be completed by April 2027. CONCLUSIONS This study is expected to provide important information regarding the role of meal timing in obesity treatment. Findings from this trial may help inform future dietary recommendations and behavioral weight management strategies. CLINICALTRIAL Clinicaltrials.gov identifier: NCT05870982. Registered trial name: Early vs Late Time Restricted Eating vs. Daily Caloric Restriction (Time2Eat). Date registered: May 4, 2023