Time-restricted eating, caloric reduction, and unrestricted eating effects on weight and metabolism

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Niki Oldenburg, Douglas G. Mashek, Lisa Harnack, Qi Wang, Emily N.C. Manoogian, Nicholas Evanoff, Donald R. Dengel, Abdisa Taddese, Brad P. Yentzer, Lesia Lysne, Alison Wong, Michelle Hanson, Julie D. Anderson, Alison Alvear, Nicole LaPage, Justin Ryder, Krista Varady, Zan Gao, Suryeon Ryu, Patrick J. Bolan et al. (4 additional authors not shown)

Published: 01 Apr 2025, Last Modified: 06 Dec 2025ObesityEveryoneRevisionsBibTeXCC BY-SA 4.0
Abstract: Objective: Metabolic improvements may precede weight loss. We compared the effects of self-selected 8-h time-restricted eating (TRE), 15% caloric restriction (CR), and unrestricted eating (UE) on weight, body composition, caloric intake, glycemic measures, and metabolic flexibility. Methods: In this 12-week randomized-controlled trial, we measured weight (primary outcome), body composition (dual-energy x-ray absorptiometry/magnetic resonance imaging), caloric intake (24-h recall), metabolic flexibility (indirect calorimetry during hyperinsulinemic-euglycemic clamp), and glycemic measures (hemoglobin A1c, hyperinsulinemic-euglycemic clamp, continuous glucose monitoring). Results: Of the 88 enrolled participants, 81 (92%) completed the trial (mean [SD], age, 43.2 [10.5] years, BMI, 36.2 [5.1] kg/m2; 54.5% female, 84.1% White). Final eating windows were 9.8 h (95% CI: 9.0 to 10.6) for TRE, 12.9 h (95% CI: 11.9 to 13.9) for CR, and 11.8 h (95% CI: 11.0 to 12.7) for UE. Compared with UE (n = 29), weight changes were −1.4 kg (95% CI: −4.5 to 1.7; p = 0.53) with TRE (n = 30) and −2.5 kg (95% CI: −5.8 to 0.8; p = 0.18) with CR (n = 29). TRE showed lower metabolic flexibility than CR (−0.041 [95% CI: −0.080 to −0.002]). Weight, body composition, caloric intake, and glycemic measures were similar among groups. Eating window reduction correlated with decreased caloric intake and visceral fat. Conclusions: In a 12-week intervention, TRE did not lead to significant improvements in weight, average body composition, or glycemic or metabolic measures compared with CR or UE.