How does fasting rebuild muscle?

Fasting can rebuild muscle through a combination of processes involving damage repair, energy reallocation, and cellular autophagy. Here's a summary of the key processes:

1. Damage and Repair: Fasting combined with exercise can initiate muscle damage, which is a trigger for subsequent muscle repair and growth. Regular exercise leads to these repetitive cycles of damage and repair, contributing to muscle building over time 1.

2. IGF-1 Redistribution: During fasting, insulin-like growth factor 1 (IGF-1) is redistributed to the muscle and brain, rather than circulating in the serum. This process is enhanced by exercise, which ensures that IGF-1 is delivered to the muscle tissues where it can aid in growth and recovery 1.

3. Autophagy and Stem Cell Activation: Fasting activates autophagy, which is the process of clearing damaged cells. This cleanup is followed by the activation of stem cells, leading to regeneration and rebuilding of not only muscle tissues but also other bodily systems. This regenerative aspect is especially potent after prolonged periods of fasting, followed by refeeding, which stimulates growth and repair 2.

4. Selective Catabolization: During fasting, energy is reallocated from less vital areas like visceral fat to more critical areas such as muscle. This selective catabolization helps in preserving lean muscle mass, while primarily using the fat stores for energy 1.

Overall, the combination of induced muscle stress (from exercise), hormonal redistribution (IGF-1), and cellular processes (autophagy and stem cell activation) contributes to muscle repair and growth during and after fasting periods.