Intermittent Fasting
The Warrior Diet (20:4): What It Is and How to Do It
The Warrior Diet is a 20:4 fasting schedule — 20 hours of undereating, a four-hour eating window at night. Here's how it works, how it differs from OMAD, and who it suits.
Photo by Nadia Valko on Unsplash
The Warrior Diet is a 20:4 schedule: roughly twenty hours fasting, then a four-hour eating window, almost always in the evening. It sits between 18:6 and OMAD on the ladder — the last rung most people can hold indefinitely.
Where 20:4 sits
| Schedule | Fasting | Eating | Who it suits |
|---|---|---|---|
| 16:8 | 16 h | 8 h | Beginners; most people, indefinitely |
| 18:6 | 18 h | 6 h | Comfortable at 16:8 for a month or more |
| 20:4 | 20 h | 4 h | Experienced fasters; the Warrior pattern |
| OMAD | ~23 h | ~1 h | Advanced only, after months at 18:6 |
The step from 18:6 to 20:4 is smaller than it looks — two hours — but it's the point where the eating window stops comfortably holding two full meals. Four hours is one large meal plus something, and that changes how you have to plan.
The original version and the practical one
As originally described, the Warrior Diet wasn't a strict fast. The twenty hours were an "undereating" phase allowing small amounts of raw fruit and vegetables, with a large evening "overeating" phase.
In practice, almost everyone now runs it as a clean 20:4 fast: water, black coffee, plain tea and electrolytes during the fasting hours, then a proper eating window at night. That's simpler, easier to track, and it keeps you genuinely fasted rather than hovering in a grey zone.
If you follow the original version with fruit and vegetables during the day, you're not fasting for twenty hours — you're eating a low-calorie diet with a large dinner. That's a legitimate way to eat, but expect the physiology of a much shorter fast. What happens in each phase is covered in The Stages of a Fast.
Why the evening window
Nearly everyone puts the four hours between about 4pm and 8pm, or 5pm and 9pm. The reasons are practical rather than metabolic:
- Dinner is the meal that's hardest to skip socially.
- You sleep after eating rather than fighting hunger at bedtime.
- Daytime hunger is easier to ride out when you're busy.
A morning window is metabolically defensible and socially miserable. If you're going to try one, have a specific reason.
How to run it
Earn it first. A month at 18:6, comfortably, before you go here. Jumping from 16:8 to 20:4 is where most people bounce. 16:8 vs 18:6 covers the progression.
Fit two feedings into four hours. A main meal plus a smaller one at the end of the window is far easier than one enormous plate — better for protein distribution and considerably more comfortable.
Protein first, every time. This is the macro you'll under-eat, and the reason 20:4 costs muscle when it does.
Break the fast deliberately. After twenty hours, what you eat first shapes the whole evening. See How to Break a Fast.
Salt through the afternoon. Hours 14 to 20 are where sodium depletion shows up as fatigue and headache. See Do Electrolytes Break a Fast?
Don't stack hard training on hour 19. Heavy sessions belong near or inside the window — see Working Out While Fasting.
Who it suits
It works well if you're already comfortable at 18:6, you prefer one substantial evening meal, your days are busy enough that daytime hunger is easy to ignore, and you're maintaining rather than chasing a hard training goal.
It's a poor fit if you're building muscle, you train hard most days, you eat lunch socially for work, or you're prone to evening overeating — a four-hour window is short enough that "make up the day's food" can turn into something less controlled.
It is not appropriate if you're pregnant or nursing, managing diabetes, taking medication that must be taken with food, or have any history of disordered eating.
20:4 versus OMAD
The four-hour window is what makes 20:4 sustainable where OMAD often isn't. Two feedings instead of one means better protein distribution, far easier nutrition, and much less digestive discomfort — for a difference in fasting hours that is metabolically minor.
If you're drawn to OMAD, run 20:4 first. Most people who try both end up back here.
Is it better than 16:8?
For fat loss, only if it makes you eat less — and a four-hour window usually does, simply because there's less time to fit food into. That's the honest mechanism: not the extra fasting hours, but the constraint on intake.
Against that, the nutrition gets harder and the social cost is real. 16:8 is a schedule you can keep for years without thinking about it. 20:4 is one you have to plan around.
Before you try this
This article is general information, not medical advice. 20:4 is an advanced schedule and is not suitable for everyone. Speak to a qualified healthcare professional before starting, particularly if you are pregnant or nursing, managing diabetes or another metabolic condition, taking medication that must be taken with food, or have any history of disordered eating.
Questions people actually ask
What can I drink during the 20-hour fast?
Water, black coffee, plain tea and unsweetened electrolytes. Anything with calories ends the fast.
Is the Warrior Diet the same as OMAD?
No. The Warrior Diet gives you a four-hour window; OMAD is roughly one hour. The extra hours make protein intake and digestion considerably easier.
Can I build muscle on 20:4?
It's possible but not ideal — two protein feedings a day is less effective than three or four. If muscle is the priority, 16:8 is the better schedule.
How long does it take to adapt to 20:4?
Usually two to three weeks if you're coming from 18:6. Coming from no fasting at all, considerably longer, and you'd do better stepping up gradually.
Should I eat my window in the morning instead?
You can, and some evidence favours earlier eating. Most people find it socially unworkable, which is why the evening window is standard.
