Hour 16
The Metabolic Shift
Sixteen hours is the minimum threshold for meaningful metabolic change. What you do now is working.
What's Happening
Ketone levels are measurable and rising. Fat oxidation is the dominant energy source. Insulin is at baseline low. The brain is beginning to run partially on ketones alongside glucose.
How You're Feeling
Energy often steadies here. The dramatic hunger of hours 8-12 tends to subside. Some people feel lighter, more alert. Cravings may shift from food-craving to specific food interest — a different feeling.