16:8 vs 18:6 vs OMAD: which fasting protocol, and when
A clear comparison of 16:8, 18:6, and OMAD — the eating windows, the metabolic phases each reaches, who each suits, and how to step between them.
16:8, 18:6, and OMAD are the same idea at three intensities: eat in a window, fast the rest. The difference is how big the window is — and that changes how far along the fasted-state phase timeline you travel each day.
The comparison
| Protocol | Fast | Eating window | Reaches | Best for |
|---|---|---|---|---|
| 16:8 | 16h | 8h | Edge of ketosis | A sustainable daily default |
| 18:6 | 18h | 6h | Start of ketosis (~18h) | More time fat-burning, still two meals |
| OMAD | ~23h | ~1h | Deep ketosis, edge of autophagy (~24h) | Experienced fasters, simple structure |
What each one reaches
- 16:8 ends right as ketone production begins, so you brush ketosis without spending real time in it.
- 18:6 pushes into the start of ketosis (~18h for most people on a normal diet).
- OMAD runs long enough to sit in ketosis and reach the edge of the autophagy band FastHQ marks from ~24h.
Those phase hours are models, not measurements — see the phase timeline for the honest caveats.
How to choose
- New to fasting? Start with 16:8. It is the most sustainable and the most studied.
- 16:8 gone stale? Step up to 18:6 for more time in the fat-burning range without much social friction.
- Want a simple, single-meal structure and already fast comfortably? OMAD — but build up to it.
The honest part
Window length is not the lever most people think it is. Total energy intake and food quality drive body-composition change far more than whether your window is eight hours or six. The protocols differ in metabolic timing and in how they fit your life — not in some hidden fat-burning magic. Pick the one you will actually keep doing.
This article is informational and not medical advice. Fasting is not for everyone; check with a doctor first if you are pregnant or breastfeeding, diabetic, underweight, or have a history of disordered eating.