The Biology Starts Within Hours, Not Days
Twelve hours after your last meal, your liver glycogen is nearly depleted. At that point, the body shifts fuel sources: free fatty acids rise, and the liver begins producing ketone bodies. This is not a dramatic event, it happens quietly, every time a fast crosses the overnight threshold. What makes religious fasting metabolically significant is that it forces this shift repeatedly, on a fixed calendar, across weeks and months of the year.
