A fast isn't one long feeling — your body moves through distinct stages, and knowing which one you're in makes the hard hours make sense.
| Hours (approx.) | Stage | What's happening |
|---|---|---|
| 0 – 4 | Anabolic (digesting) | Your body is still processing the last meal; insulin is high |
| 4 – 8 | Settling | Insulin falls; glycogen stores start being drawn down |
| 8 – 12 | The switch | Glycogen runs low; fat becomes the main fuel |
| 12 – 18 | Fat burning & early ketosis | Ketone production rises — this is where 16:8 fasters spend their final hours |
| 18+ | Deeper ketosis | Longer fasts deepen ketosis; autophagy is discussed in research — mostly animal studies, and human timing isn't settled |
The numbers are approximate and shift with your last meal, activity, and body. The practical part is simply knowing where you are right now — which is exactly what Orbo draws on the ring while you fast. New to this? Start with the 16:8 guide.
Typically between hours 12 and 16, once glycogen runs low — earlier or later depending on your last meal and activity.
Human research hasn't pinned an exact hour; most cited findings come from animal studies and fasts longer than 16 hours.
As ketones rise your brain uses them for fuel, which many people experience as late-fast clarity.
Watch your stages live on the ringOrbo shows your current stage and the countdown to the next one