Key Takeaway
Meta-analysis of long-term IF studies (12+ weeks) shows sustained reductions in body weight, fat mass, and cardiometabolic markers in overweight/obese adults without excessive muscle loss.
Summary
This systematic review and meta-analysis specifically examined longer-term studies of intermittent fasting (12 weeks or more) in adults with overweight or obesity. The focus on extended duration addresses a key gap in the IF literature, where most studies are short-term.
The analysis found that IF protocols maintained over 12+ weeks produced meaningful and sustained improvements in body composition. Weight loss averaged 3-5 kg, with significant reductions in fat mass. Importantly, lean mass was largely preserved, addressing concerns that fasting might accelerate muscle loss. Cardiometabolic markers including fasting glucose, insulin, blood pressure, and some lipid parameters also improved.
The findings support IF as a sustainable long-term dietary strategy for metabolic health. The preservation of lean mass is particularly notable, suggesting that when combined with adequate protein intake during eating windows, IF does not compromise muscle mass any more than traditional caloric restriction.
Methods
- Systematic review following PRISMA 2020 guidelines
- Searched PubMed, Scopus, Web of Science, Cochrane Library
- Included RCTs with IF interventions lasting ≥12 weeks
- Participants: Adults with overweight (BMI ≥25) or obesity (BMI ≥30)
- IF protocols: Time-restricted eating, alternate day fasting, 5:2 diet
- Primary outcomes: Body weight, fat mass, lean mass
- Secondary outcomes: Fasting glucose, insulin, lipids, blood pressure
- Meta-analysis using random effects models
Key Results
- Body weight: Significant reduction (MD: -3.2 to -5.1 kg vs. control)
- Fat mass: Significant reduction with preserved lean mass
- Lean mass: Minimal loss, not significantly different from control/caloric restriction
- Fasting glucose: Modest but significant reduction
- Fasting insulin: Significant improvement
- HOMA-IR: Improved insulin sensitivity
- Blood pressure: Reductions in both systolic and diastolic BP
- LDL cholesterol: Mixed results; some improvement in subset analyses
- Triglycerides: Significant reduction in most analyses
- Adherence: Generally high in longer-term studies
Limitations
- Heterogeneity in IF protocols and fasting durations
- Most studies still 12-24 weeks; very few beyond 6 months
- Self-reported dietary adherence in most studies
- Limited data on very long fasts (48-72+ hours)
- Predominantly female participants in many studies
- Cannot determine optimal eating window or fasting schedule
- Few studies measured muscle strength or physical performance
- Publication bias possible
- Most studies conducted in Western populations