You can look at Dr Filinov’s website which is in Russian using Google translate for an excellent resource on this.
Each cell of the body turns into a tiny furnace and starts burning toxins and fat during a dry fast. They create high quality metabolic water which is the reason one pees roughly twice even on a dry fast per day.
Dry fasting is said to be 3x quicker in its functioning than a water fast: it is also easier tolerated (can attest).