What are the benefits and risks of intermittent fasting (IF) for athletes?

Intermittent Fasting for Athletes: Benefits and Risks

Intermittent fasting (IF) may provide benefits for athletes including improved body composition without reducing physical performance, but should be implemented cautiously as it can increase risk of disordered eating and negatively impact training adaptations.

Benefits of Intermittent Fasting for Athletes

Time-restricted eating (TRE), a form of intermittent fasting, has shown several potential benefits for athletes:

• Body Composition Improvements:

  • Reduces body weight (approximately 2%) and fat mass percentage (1.1%) while preserving fat-free mass 1
  • May improve power-to-weight ratio in endurance athletes 1

• Performance Maintenance:

  • Most studies indicate that IF doesn't significantly reduce physical performance when properly implemented 2
  • Can maintain strength, power, and aerobic capacity when energy intake is adequate 2

• Metabolic Benefits:

  • Promotes metabolic shifts in energy production
  • Optimizes peripheral circadian clocks
  • May improve physiological markers of metabolic health 3

• Reduced Inflammation:

  • Can decrease the neutrophils-to-lymphocytes ratio (NLR), suggesting reduced inflammation 1
  • May have a protective effect on some components of the immune system 1

Risks and Considerations

Despite potential benefits, several important risks must be considered:

• Disordered Eating Risk:

  • IF can potentially progress to disordered eating (DE) behaviors in susceptible athletes 4
  • Athletes are already at higher risk for DE compared to non-athletes (0-19% in men, 6-45% in women) 4

• Energy Availability Concerns:

  • Low energy availability (LEA) may occur with improper IF implementation
  • LEA can lead to relative energy deficiency in sport (RED-S) with multiple health consequences 4

• Training Adaptations:

  • Prolonged training in the fasted state may not allow optimal adaptation of muscles and tissues 5
  • May compromise recovery between training sessions

• Hormone Disruption:

  • Can decrease anabolic hormones like free testosterone and IGF-1 1
  • May affect reproductive hormones, especially in female athletes 4

Implementation Guidelines

For athletes considering intermittent fasting:

1. Maintain Total Energy Intake:

   • Ensure 100% of estimated daily energy needs are consumed within the feeding window 1
   • Protein intake should be at least 1.2 g/kg body mass/day for optimal immune function 4

2. Choose Appropriate IF Protocol:

   • Time-restricted eating with an 8-hour feeding window (e.g., 10:00 a.m. to 6:00 p.m.) has shown benefits 1
   • Consider overnight fasting as a less extreme approach 2

3. Monitor Performance and Recovery:

   • Track training performance, recovery, and subjective feelings of fatigue
   • Be prepared to adjust or discontinue IF if performance declines

4. Periodize Nutrition Approach:

   • Consider using IF during specific training phases rather than year-round
   • Avoid IF during competition periods or high-intensity training blocks

5. Screen for Risk Factors:

   • Athletes with history of disordered eating should avoid IF 4
   • Female athletes should monitor menstrual function as an indicator of energy availability 4

Special Considerations

• Individual Variability: Response to IF varies significantly between individuals 6
• Training Schedule: Align feeding windows with training sessions when possible
• Hydration: Maintain adequate hydration even during fasting periods
• Sleep Quality: Monitor and maintain sleep quality, as IF may affect sleep patterns

Conclusion

While intermittent fasting shows promise for improving body composition without compromising performance in athletes, it must be implemented carefully with attention to total energy intake, nutrient timing, and individual response. The risk of developing disordered eating behaviors means that IF should be avoided in athletes with a history of eating disorders or those at high risk. For healthy athletes, IF may be considered as part of a periodized nutrition approach rather than a constant dietary strategy.