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Updated: Mar 15, 2026

Assessment of the Metabolic Effects of Isocaloric 2:1 Intermittent Fasting in Mice
Published on: November 27, 2019
A randomized pilot study comparing zero-calorie alternate-day fasting to daily caloric restriction in adults with
Victoria A Catenacci1,2, Zhaoxing Pan3, Danielle Ostendorf2,4
1Department of Medicine, Division of Endocrinology, Metabolism, and Diabetes, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.
Objective:
To evaluate the safety and tolerability of alternate-day fasting (ADF) and to compare changes in weight, body composition, lipids, and insulin sensitivity index (Si) with those produced by a standard weight loss diet, moderate daily caloric restriction (CR).
Methods:
Adults with obesity (BMI ≥30 kg/m(2) , age 18-55) were randomized to either zero-calorie ADF (n = 14) or CR (-400 kcal/day, n = 12) for 8 weeks. Outcomes were measured at the end of the 8-week intervention and after 24 weeks of unsupervised follow-up.
Results:
No adverse effects were attributed to ADF, and 93% completed the 8-week ADF protocol. At 8 weeks, ADF achieved a 376 kcal/day greater energy deficit; however, there were no significant between-group differences in change in weight (mean ± SE; ADF -8.2 ± 0.9 kg, CR -7.1 ± 1.0 kg), body composition, lipids, or Si. After 24 weeks of unsupervised follow-up, there were no significant differences in weight regain; however, changes from baseline in % fat mass and lean mass were more favorable in ADF.
Conclusions:
ADF is a safe and tolerable approach to weight loss. ADF produced similar changes in weight, body composition, lipids, and Si at 8 weeks and did not appear to increase risk for weight regain 24 weeks after completing the intervention.
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