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Intermittent Fasting and Fat-Free Mass Outcomes in Middle-Aged and Older Adults: A Scoping Review
Sara Santero1, Bojana D Blagojević2, Mohammed Merzah3
1Laboratory of Dietetics and Clinical Nutrition, Department of Public Health, Experimental and Forensic Medicine, University of Pavia, Pavia, Italy.
Advances in Nutrition (Bethesda, Md.)
|July 16, 2026
Summary
Intermittent fasting (IF) shows comparable fat loss to continuous energy restriction but its effect on fat-free mass (FFM) in older adults remains unclear. More long-term studies are needed for definitive conclusions on IF and healthy aging.
Area of Science:
- Gerontology and Nutritional Science
- Metabolic Health and Body Composition Research
Background:
- Aging is associated with natural muscle mass decline.
- Intermittent fasting (IF) is a popular weight-loss strategy.
- Concerns exist regarding IF's impact on fat-free mass (FFM) in aging populations.
Purpose of the Study:
- To review evidence on IF's effects on FFM in adults aged 45 and older.
- To compare IF with habitual diet (HD) and continuous energy restriction (CER).
- To assess IF's impact on other anthropometric, functional, and quality of life outcomes.
Main Methods:
- Systematic review of randomized controlled trials (RCTs) published between 2000-2025.
- Included studies involved adults ≥45 years, IF ≥4 weeks, and validated FFM measures.
- Excluded participants with disease-related muscle loss.
Main Results:
- Twenty RCTs (1653 participants) were included, primarily overweight/obese adults.
- IF resulted in fat mass, body weight, and waist circumference reductions comparable to CER.
- IF consistently reduced body weight and fat mass compared to HD, particularly alternate-day fasting protocols.
Conclusions:
- Current evidence is insufficient to conclude IF's long-term impact on FFM preservation in older adults.
- Most studies had short durations (≤12 weeks) and lacked methodological standardization.
- Further long-term, high-quality trials with standardized muscle and functional outcomes are necessary.
