Is 16:8 actually effective?

16:8 is the most studied and most sustainable intermittent-fasting pattern, mainly because people stick with it. It is effective for the thing it is for: a repeatable daily structure. It is not magic, and results depend on what you eat in the window and your overall energy balance.

Does 16:8 get me into ketosis?

Usually not deeply. A 16-hour fast ends right around the time ketone production typically starts climbing (~16–18h), so most people only touch the edge of ketosis on 16:8. If reaching ketosis is your goal, an 18:6 or longer protocol spends more time there. See the phase timeline for the hour-by-hour detail.

Can I drink coffee during the fast?

Black coffee, plain tea, and water are fine and do not meaningfully break a fast. Anything with calories — milk, sugar, sweeteners that trigger an insulin response — moves you out of the fasted state.

Is 16:8 free in FastHQ?

Yes. 16:8 is the free default protocol, with no time limit and no ads. Pro ($3.99/month) unlocks 18:6, OMAD, 24h, custom windows, phase tracking, and a year of history.

16:8 intermittent fasting: the daily default, timed to the second

16:8 is intermittent fasting’s default setting: fast for 16 hours, eat within an 8-hour window, repeat daily. It is popular for a boring, good reason — it fits around normal life. You skip breakfast, eat lunch and dinner, and the fast mostly happens while you sleep.

This page is the precise version: how to run it, what each hour does, and where the honest limits are.

How to run a 16:8 fast

Pick an 8-hour eating window that fits your day — a common one is 12:00–20:00.
Log your last meal. FastHQ starts the clock at the exact second you finish, not at a rounded hour.
Fast for 16 hours. Water, black coffee, and plain tea are fine.
Open the window, press stop, and log it — complete or broken, recorded to the second.

That is the entire protocol. There is no auto-detection guessing whether you ate, and no streak nagging you to keep a chain alive.

What happens during a 16-hour fast

A 16-hour fast walks you through the first part of the fasted-state phase timeline:

0–4h — digesting. You are still absorbing your last meal.
4–12h — fasting. Meal glucose is used up; your body draws on stored liver glycogen.
12–16h — gluconeogenesis begins. Glycogen runs low, the liver starts making glucose from other sources, and fat-burning rises.

A 16-hour fast typically ends right as ketone production starts to climb — which is why 16:8 brushes the edge of ketosis without spending real time there. If that is your goal, 18:6 or OMAD go further.

Who 16:8 is for

16:8 suits almost anyone starting a sustainable daily routine, and anyone who wants the structure without thinking about it. It is gentle enough to run every day and flexible enough to shift your window earlier or later.

It is not the right tool if you are chasing deep autophagy or extended-fast benefits — those need longer windows. And like any fasting pattern, it is not for everyone: talk to a doctor first if you are pregnant or breastfeeding, diabetic, underweight, or have a history of disordered eating.

Common mistakes

Treating the window as a free-for-all. 16:8 structures when you eat, not what. A window of junk is still junk.
Rounding the clock. “About 16 hours” drifts. FastHQ times the real interval so your log means something.
Chasing ketosis on a 16-hour fast. The math rarely works — step up the protocol instead.

Want the hour-by-hour metabolic detail? Read the fasted-state phase timeline. Ready to start? Get notified when FastHQ ships.