…and exercise yourself toward godliness. For bodily exercise profits a little, but godliness is profitable for all things, having promise of the life that now is and of that which is to come. This is a faithful saying and worthy of all acceptance. (1Tim 4:7-9)
An important part of God's exercise program is... fasting.
02 Fasting - Spiritual Strengthening- Podcast
Fasting (Teaching notes pdf)