A 1-year Randomized Trial Comparing Modified Intermittent Fasting to Daily Caloric Restriction

Background: Intermittent fasting (IMF) paradigms have gained attention as an alternative dietary weight loss strategy, but longer-term randomized trials evaluating efficacy are limited. Our objective was to compare changes in weight from modified IMF (mIMF, 80% energy restriction on three nonconsecutive days/week) versus daily caloric restriction (DCR) over 1 year. Methods: 165 adults (mean ± SD; age 42 ± 9 years, BMI 34.2 ± 4.3 kg/m2, 74% female, 86% white, 24% Hispanic), without diabetes mellitus, cardiovascular disease, or chronic kidney disease (stage 4 or 5) were randomized to mIMF (n = 84) or DCR (n = 81) for 1 year. The targeted weekly dietary energy deficit was designed to be similar in mIMF and DCR (34%). Both intervention arms received group-based behavioral support including guidance on the randomized dietary strategy and a recommendation to increase moderate-intensity physical activity to 300 min/week. Intervention arms met separately; group meetings were held weekly for months 0-3 and every other week for months 4-12. The primary outcome was change in body weight (kg, calibrated digital scale) at 1 year. Secondary outcomes included changes in body composition (DXA), self-reported energy intake (El, 7-day diet diaries), total daily energy expenditure (TDEE; doublylabeled water), blood pressure (BP), fasting lipid panel, fasting glucose, and Hbalc. Linear mixed models were used to examine the association between randomized group and change in outcomes over 1 year using an intent-to-treat analysis. Results are mean ± SE, unless otherwise stated. Results: There were no significant differences between groups in baseline characteristics, retention, or group-session attendance. At 1 year, mIMF demonstrated greater reductions in weight (-7.7 ± 1.0 vs -4.8 ± 1.1 kg; p = 0.04), lean mass (-1.8 ± 0.3 vs -0.6 ± 0.4 kg; p = 0.01), and self-reported El (-524 ± 51 vs -221 ± 52 kcal/d; p < 0.01) versus DCR. There were no significant between-group differences in changes in fat mass (mIMF: -5.9 ± 0.8; DCR: -3.8 ± 0.8 kg, p = 0.07), TDEE, systolic BP, diastolic BP, total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides, fasting glucose, or Hbalc at 1 year. Conclusions: Compared to DCR, mIMF was more effective for weight loss over 1 year among healthy adults with overweight or obesity enrolled in group-based behavioral weight loss program.