What happens to your muscles when you don't eat for a week?
Effects of seven days’ fasting on physical performance and metabolic adaptation during exercise in humans
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Surprising Findings
Maximal muscle strength stayed the same despite losing nearly 5 kg of lean mass.
Most assume muscle loss equals weakness, but the body seems to preserve functional contractile proteins even while breaking down other tissue.
Practical Takeaways
If you're fasting for health or weight loss, don’t expect strength gains, but don’t fear immediate weakness either.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Surprising Findings
Maximal muscle strength stayed the same despite losing nearly 5 kg of lean mass.
Most assume muscle loss equals weakness, but the body seems to preserve functional contractile proteins even while breaking down other tissue.
Practical Takeaways
If you're fasting for health or weight loss, don’t expect strength gains, but don’t fear immediate weakness either.
Publication
Journal
Nature Communications
Year
2025
Authors
Kristoffer J. Kolnes, Emelie T. F. Nilsen, Steffen Brufladt, Allison M. Meadows, P. Jeppesen, Ø. Skattebo, E. Johansen, J. Birk, K. Højlund, J. Hingst, B. S. Skålhegg, R. Kjøbsted, J.L. Griffin, A. Kolnes, S. O’Rahilly, J. Wojtaszewski, J. Jensen
Related Content
Claims (6)
If healthy young people don't eat for a week, their muscles might switch how they burn fuel during exercise—using less sugar—which could make it harder to keep up with endurance activities.
Fasting for a week doesn't seem to change a key energy sensor in young healthy people's muscles, which suggests it might not be what causes muscle breakdown during fasting.
If healthy young people don't eat for a week but stay active, they might lose muscle mass but still keep their leg strength — meaning their muscles might protect the parts that actually make them strong.
If healthy young people stop eating for a week, their ability to perform intense exercise—like running fast or cycling hard—gets worse by about 13%, even though their muscles are still just as strong.
If healthy young people don’t eat for a week, their muscles lose half their stored energy from carbs, but they can still work just as hard during intense exercise.