Effects of Seven Days of Fasting on Physical Performance and Metabolic Adaptation
Author Information
Author(s): Kolnes Kristoffer J., Nilsen Emelie T. F., Brufladt Steffen, Meadows Allison M., Jeppesen Per B., Skattebo Øyvind, Johansen Egil I., Birk Jesper B., Højlund Kurt, Hingst Janne, Skålhegg Bjørn S., Kjøbsted Rasmus, Griffin Julian L., Kolnes Anders J., O’Rahilly Stephen, Wojtaszewski Jørgen F. P., Jensen Jørgen
Primary Institution: Norwegian School of Sport Sciences, Oslo, Norway
Hypothesis
How does seven days of fasting affect physical performance and metabolic adaptation during exercise in humans?
Conclusion
Maximal leg muscle strength was preserved during fasting, but maximal oxygen uptake and work capacity decreased by about 15%.
Supporting Evidence
- Participants lost an average of 4.6 kg of lean mass and 1.4 kg of fat mass after fasting.
- Maximal isometric and isokinetic strength remained unchanged after fasting.
- Peak oxygen uptake decreased by 13% after fasting.
- Muscle glycogen was halved during the fasting period.
- PDK4 expression increased 13-fold during fasting.
Takeaway
When people fast for a week, they can still be strong, but they might get tired more easily when exercising.
Methodology
Thirteen participants completed a seven-day water-only fasting intervention, with daily evaluations and physical performance tests before and after fasting.
Potential Biases
Participants were all healthy young adults, which may not represent the general population.
Limitations
The study lacked a randomized control group and had a relatively small sample size, limiting generalizability.
Participant Demographics
Thirteen participants (7 males and 6 females), aged approximately 29.7 years.
Statistical Information
P-Value
p<0.00001
Statistical Significance
p<0.05
Digital Object Identifier (DOI)
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