Most people think a fast is a fast. It is not. Water fasting drives autophagy one way, by suppressing the nutrient sensor mTOR. Dry fasting adds a second route, hyperosmotic stress, that forces a deeper cleanup near the nucleus. Here is why that depth is the whole difference.
Water fasting is gentler and easier to sustain but shallower. Dry fasting is far more powerful per day but aggressive and demanding. Here is how I decide which one a chronically ill person should actually do, and who should not lead with a dry fast.
Dry fasting is not water fasting with the water turned off. It activates a second, independent autophagy pathway that water fasting cannot reach, which is why one day of dry fasting produces roughly the same depth of cellular cleanup as three days of water fasting. This article explains the real difference.