When you consume nothing but water for several days, you get tired. It’s natural to interpret this fatigue as a sign that the fast is harming your health, but I believe that this subjective sensation of fatigue is just the body’s way of asking you to rest. While eating a meal and then drinking a cup of coffee is like an upshift, a meditative water fast is like a downshift. Coffee is a great tool if used in moderation, but overdoing it can lead to burning the candle at both ends. A rested water fast, on the other hand, is like burning the candle at neither end. It’s the opposite of a stimulant. Your body gets a chance to put all its effort into recovery.
If you’re living life as normal, your body will try to heal any damaged joints, but the autophagy will remain minimal. You can’t break something down too much if you’re going to use it again soon! But when you’re out of commission during a fast, your body can go much deeper with the autophagy. And then during the recovery from the fast, your body can build things back up like new.
As an analogy, imagine that you’re in charge of a supermarket that’s open from 9 AM to midnight every day. You can have your employees do a bit of restocking, cleaning, and repair throughout the day, but you can’t get in the way of the customers too much, as that would defeat the purpose of the business. And you can have a night crew do some deeper projects. But what if you want to do something so radical that your store is rendered unusable for a whole week? You’d need to close to renovations.
That I believe is a good illustration of the difference between normal life and a water fast. During normal life, your body can do light projects, but anything too disruptive is out of the question. During a water fast, however, you body can go as far as knocking down walls, removing old floorboards, and spilling paint all over old carpets you’re about to throw away. You’re closed for renovations!