Fasting isn’t going to get you “in shape”, you need some sort of exercise for that.

Peter Attia who has done extensive self-experimentation with fasting for health and uses it in his medical practice noted that without strength training during fasts his body fat really increased.

https://www.menshealth.com/fitness/a37508857/intermittent-fa...

I'm a Christian. One of the key points of fasting is to humble yourself; it is a way of saying "food is less important than my relationship with God".