Introduction: Time-restricted eating (TRE) has cardiometabolic health benefits by optimizing circadian rhythms. However, limited data are available on the effect of early TRE in young adults. The objective of this pre-post single-arm trial was to test the effect of TRE on body composition and cardiometabolic risk factors and to evaluate changes in meal and sleep timing by TRE among young adults with typically late bedtime. Methods: This 4-week intervention was conducted in healthy young adults aged 18-30 years. Dietary records with time logs were collected before and during the intervention and nutrient intake and meal timing were evaluated. Snack packages containing 20 g/day of protein were provided weekly. Body composition was measured weekly using bioelectrical impedance analysis. Blood samples were collected before and after the intervention, and cardiometabolic parameters were evaluated. Results: Of the 36 screened participants, 34 completed the study (completion rate 94.4%). The average age was 23.4 ± 2.9 years with 64.7% female. The mean wake-up time and bedtime were 09:16 ± 01:26 and 01:51 ± 01:39 with average sleep duration of 7.4 ± 1.4 hour. Body weight and fat mass, excluding muscle mass, were significantly reduced over 4 weeks compared to baseline only in the early TRE group starting before noon. The early TRE group also showed significantly reduced fasting glucose, fasting insulin, and serum triglyceride (TG) levels after 4 weeks. However, the late TRE group starting after noon showed no significant changes except a reduced TG level. The meal timing was changed by TRE, where the first meal was delayed and the last meal was shifted. Neither sleep duration nor timing was significantly changed by TRE. Energy intakes was not different, but protein intake increased from 19.2% to 22.6% due to snack packages during intervention. However, no significant correlation between nutrient intakes and body composition changes was found. There were no adverse events related to study participation. Conclusions: An early TRE regimen may be a feasible and effective strategy to manage body composition and cardiometabolic risk factors in young adults, without altering the sleep–wake cycle. Trial Registration: The Clinical Research Information Service (CRIS.nih.go.kr) identifier: KCT0006443

The Author(s). Published by S. Karger AG, Basel