Introduction
Intermittent fasting (IF) and other fasting strategies are increasingly adopted by athletes seeking to improve their body composition, metabolic health, and performance. Yet, as research shows, the effects of fasting on athletic outcomes are mixed, offering both potential benefits and risks depending on the context and execution.
What the Evidence Reveals
1. Body Composition & Metabolic Adaptations
Intermittent fasting can enhance lean body composition, fat oxidation, and even maximal power output without compromising performance in some settings. A 2023 systematic review of 25 studies found that IF supports improved body composition and maintains lean mass while preserving performance metrics, such as maximal power (PubMed). Another meta-analysis indicates that IF encourages fat oxidation, preserves glycogen, and may benefit endurance athletes through metabolic flexibility MDPI.
2. Endurance vs. High-Intensity Performance
Time-restricted eating (e.g., 16:8 fasting) has helped decrease body fat in endurance athletes without impairing VO₂max or endurance performance—and sometimes even improved power-to-weight ratios, according to MDPI. However, Ramadan-style fasting has been associated with reduced sprint performance, particularly in the morning, while other metrics like aerobic capacity and jump height remain mostly unaffected PubMedMDPI.
3. Strength Training & Power
For strength-focused athletes, the findings are encouraging: IF, combined with resistance training, can produce gains in muscle mass, strength, and endurance comparable to those achieved with non-fasting strategies (MDPI, The Conversation, Health). One study with female CrossFit athletes found that a 24-hour fast did not impair performance, jump distance, grip strength, or heart rate metrics—although it did alter lactate levels.
4. Performance Drawbacks & Risks
Specific athletic capacities, especially anaerobic performance (e.g., sprints, power output), may decline during fasting periods. Repeated sprints and high-intensity efforts demonstrated decreased speed and power, linked to reduced vertical stiffness, following short-term fasting. The Conversation, Reddit. Additionally, risks such as increased fatigue, dehydration, altered sleep patterns, and increased perceived exertion have been noted, especially under prolonged fasting conditions or during Ramadan. Fasting may also carry psychological risks and be unsuitable for athletes prone to disordered eating or those with high energy demands, MDPI, The Conversation.
Best Practices & Practical Considerations
- Meal Timing Matters
- For resistance training and recovery, scheduling workouts within or shortly after the eating window (e.g., 16:8) optimizes muscle protein synthesis and performance.
- Know Your Sport & Individual Response
- Fasting may benefit endurance activities via fat utilization, but repeating sprints or explosive efforts may suffer. Monitor performance trends and adapt accordingly. The Conversation.
- Stay Hydrated & Recover Well
- Especially during Ramadan-style fasts, prioritize hydration, sleep, and nutrient timing to mitigate performance declines. Dove Medical Press, AP News, Verywell Health.
- Use It Strategically
- IF might be used during off-season phases for body composition goals, but avoid during high-stakes competition periods or when training demands are high.
- Consult Professionals
- Work with a sports dietitian or coach to tailor fasting to your schedule, sport, and recovery needs—particularly for female athletes and those with unique health considerations.
Conclusion
Fasting can offer significant benefits for athletes—such as improved body composition, enhanced metabolic flexibility, and even preserved strength—especially when combined with strategic training and nutrition approaches. However, it's not universally advantageous; high-intensity performance, hydration status, and individual variability make tailoring and caution essential. When managed effectively, fasting can be a valuable tool in an athlete’s toolbox—but context and customization are crucial.
References (APA 7th Edition)
- HealthNews. (n.d.). Intermittent fasting for athletes: Is it a way to go? WellnessPulse
- MDPI. (2024). Intermittent fasting: Does it affect sports performance? A systematic review. PubMed
- MDPI. (n.d.). Effects of intermittent fasting and calorie restriction on exercise performance: A systematic review and meta-analysis. MDPI
- MDPI. (2023). Time-restricted eating (16:8) in endurance runners. MDPIReddit
- MDPI. (2023). 24-h fasting in female CrossFit athletes. PMCMDPI
- PubMed. (n.d.). Ramadan Fasting and Physical Performance: A Systematic Review. PubMed
- Health (2025, August). Optimal timing for strength training during fasting. Health
- Verywell Health. (2024, 11 months ago). Working out while fasting: Is it safe? Verywell Health
- The Conversation. (n.d.). How does intermittent fasting affect athletic performance? The Conversation