Journal of Nutrition,Fasting and Health

Journal of Nutrition,Fasting and Health

Investigation of the Effects of Eight Weeks of Intermittent Fasting (16:8 Pattern) on Body Composition, Aerobic Capacity, and Hormonal and Metabolic Indices in Competitive Swimmers

Articles in Press

Document Type : Research Paper

Authors
Mostafa Tayebi 1
afsaneh rohany 2
Zohreh Borhani Kakhki 1
1 Department of Physical Education, Farhangian University, Tehran, Iran.
2 PhD in Sport Management; Physical Education Teacher, District 1, Tehran Department of Education, Tehran, Iran
10.22038/jnfh.2026.93964.1616
Abstract
Introduction: Intermittent fasting (IF) has recently received attention as a nutritional strategy to improve athletic performance and body composition. Despite its proposed benefits for enhancing fat oxidation and insulin sensitivity, its effects on mixed-type sports such as swimming remain unclear. This study examined the effects of IF on performance, body composition, and metabolic indices in competitive swimmers. Methods: In a quasi-experimental design with pre-test/post-test and a control group, 24 male swimmers (Tehran Premier League, aged 18–25) were randomly assigned to IF and control groups. The IF group followed a 16:8 schedule for 8 weeks (fasting 23:00–15:00; feeding 15:00–23:00). The control group maintained usual eating. Both groups completed similar swim training (endurance, speed, and technique) three sessions per week. Variables included body fat percentage (%BF; InBody), VO2max (Cooper test in water), 100-m freestyle time, and serum insulin and cortisol. Data were analyzed using independent t-tests and ANCOVA in SPSS-26 (alpha = 0.05). Results: After 8 weeks, the IF group showed a significant reduction in body fat (approximately −15.4%; p = 0.001), a significant increase in VO2max (p = 0.03), improved 100-m freestyle time .p = 0.005), and a significant decrease in serum insulin (p = 0.02), while cortisol exhibited a slight increase (p = 0.04). No significant changes were observed in the control group. Conclusion: A time-restricted IF (16:8) protocol appears to be a low-cost, effective approach to improving body composition, aerobic performance, and insulin levels in competitive swimmers. Although the mild increase in cortisol warrants monitoring, the regimen was evaluated as safe and effective over a short period.
Keywords
Intermittent fasting
Athletic performance
Body composition
Metabolic indices
Competitive swimmers
Subjects
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Journal of Nutrition,Fasting and Health

Articles in Press, Accepted Manuscript
Available Online from 10 November 2026

  • Receive Date 30 December 2025
  • Revise Date 12 March 2026
  • Accept Date 22 June 2026