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Updated: Jul 14, 2026
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Assessment of the Metabolic Effects of Isocaloric 2:1 Intermittent Fasting in Mice
Published on: November 27, 2019
Duration-Dependent Changes in Body Composition During Prolonged Fasting: A Systematic Review and Meta-Analysis.
Süleyman Ulupınar1, Merve Terzi2, Ayşe Çamli3
1Faculty of Sport Sciences, Erzurum Technical University, Erzurum 25050, Türkiye.
Nutrition Reviews
|July 13, 2026
Summary
Prolonged fasting effectively reduces body weight and fat mass but also leads to significant losses in lean body mass and water. These complex body composition changes occur regardless of fasting duration, highlighting the need for careful consideration.
Area of Science:
- Nutrition Science
- Metabolic Health
- Body Composition Analysis
Background:
- Prolonged fasting is a popular non-pharmacological method for weight reduction and metabolic health.
- Understanding the precise impact of fasting on body composition (fat mass, fat-free mass, total body water) is crucial.
- The influence of fasting duration on these compositional changes requires further clarification.
Purpose of the Study:
- To systematically review and meta-analyze the effects of prolonged fasting on various body composition outcomes.
- To quantify the magnitude of changes in body weight, BMI, fat mass, fat-free mass, total body water, and waist circumference.
- To investigate the role of fasting duration, baseline weight status, and assessment methods in modulating these effects.
Main Methods:
- Systematic literature search across PubMed, Web of Science, and Scopus databases.
- Inclusion of studies reporting pre-post body composition changes.
- Meta-analysis using standardized mean changes (Hedges' g) and random-effects models.
- Subgroup analyses and meta-regression to explore effects of fasting duration (≤3 days vs >3 days), weight status, and assessment methods.
Main Results:
- Prolonged fasting significantly reduced body weight (g=-0.38) and BMI (g=-0.42).
- Significant decreases were observed in fat mass (g=-0.25), fat-free mass (g=-0.51), total body water (g=-0.68), and waist circumference (g=-0.55).
- Weight loss was greater in obese individuals and more pronounced with fasting durations exceeding 3 days, though duration-response relationships were not consistently significant across all outcomes.
Conclusions:
- Prolonged fasting leads to reductions in body weight, BMI, fat mass, and waist circumference.
- Fasting-induced weight loss involves substantial losses in both fat-free mass and total body water, not solely fat.
- No clear duration-dependent effects were consistently observed for most body composition changes.
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