The Effect of 4:3 Intermittent Fasting on Weight Loss at 12 Months: A Randomized Clinical Trial

Background: Long-term (>= 12 months) randomized trials evaluating the efficacy of intermittent fasting (IMF) as a dietary weight loss strategy are limited. Furthermore, no studies have compared IMF versus daily caloric restriction (DCR) when both interventions are provided in the context of a guidelines-based behavioral weight loss program. Objective: To compare the effects of 4:3 IMF versus DCR on changes in weight at 12 months, with comprehensive behavioral support provided to both groups. Design: Randomized clinical trial. (ClinicalTrials.gov: NCT03411356) Setting: Denver, Colorado, and surrounding metropolitan area. Participants: Adults aged 18 to 60 years with body mass index (BMI) of 27 to 46 kg/m(2). Intervention: The IMF group was instructed to restrict energy intake by 80% on 3 nonconsecutive days per week, with ad libitum intake (no restriction) the other 4 days (4:3 IMF). The DCR group was instructed to reduce daily energy intake by 34% to match the weekly energy deficit of 4:3 IMF. Both groups received a high-intensity comprehensive behavioral weight loss program that included group-based behavioral support and a recommendation to increase moderate-intensity physical activity to 300 minutes per week. Measurements: The primary outcome was change in body weight (in kilograms) at 12 months. Results: Of the 165 (4:3 IMF, n = 84; DCR, n = 81) randomly assigned participants (mean age, 42 years [SD, 9]; mean BMI, 34.1 kg/m(2) [SD, 4.4]; 73.9% female), 125 completed the trial. In an intention-to-treat analysis, 4:3 IMF showed greater reductions in weight than DCR at 12 months (mean difference, 2.89 kg [95% CI, 5.65 to 0.14 kg]; P = 0.040). Limitation: Limited generalizability. Conclusion: Compared with DCR, 4:3 IMF resulted in modestly greater weight loss among adults with overweight or obesity enrolled in a 12-month, high-intensity, comprehensive behavioral weight loss program.