20:4 Fasting Schedule (Warrior Diet): Plan, Sample Day, Risks
20:4 — sometimes called the Warrior Diet — fasts for 20 hours and concentrates eating into 4. It's an advanced protocol best attempted after weeks of 18:6. The metabolic benefits are real, but so is the difficulty of meeting protein and energy needs in such a tight window.
How 20:4 works
A 4-hour eating window typically runs 16:00–20:00 or 17:00–21:00. Most people eat one main meal at the open of the window and a second smaller meal before close. Hydration matters more here — aim for 3 L of water spread through the fasting hours, plus electrolytes.
A sample day
- 07:00Wake up. Water + sea-salt pinch.
- 10:00Black coffee. More water.
- 13:00Hunger peak — push through with water and a brisk walk.
- 16:00Break fast: large protein + vegetables + carbs + fat.
- 19:30Second meal: lighter protein + fruit + nuts.
- 20:00Close window.
- 20:00–16:00Fasting window. Water and tea only.
What happens in your body
Physiological milestones reached during a 20-hour fast.
- h4
Blood sugar normalizes
Insulin drops back to baseline as your last meal finishes digesting.
- h8
Glycogen burning begins
Your liver starts releasing stored glycogen to keep blood glucose steady.
- h12
Glycogen depletion
Liver glycogen runs low; the body shifts toward fat for fuel.
- h14
Fat burning accelerates
Lipolysis ramps up — stored triglycerides break down into free fatty acids.
- h16
Mild ketosis starts
The liver begins producing ketones from fatty acids. Mental clarity often improves here.
- h18
Growth hormone rises
HGH increases up to 5×, supporting muscle preservation and tissue repair.
What to eat
You only have 4 hours so maximize density — two palms of protein at the first meal, vegetables to fullness, a thumb of healthy fat, and a cupped hand of starchy carbs around training. The second meal can be lighter but still hit ~25 g protein.
How to break the fast
- Salmon with roasted potatoes and a big salad
- Steak fajita bowl with rice, beans, and avocado
- Lamb curry with lentils and steamed greens
- Roasted chicken thighs with quinoa and grilled vegetables
Who it's for
- • Experienced intermittent fasters
- • People who eat well in fewer, larger meals
- • Those targeting deeper ketosis without committing to extended fasting
Benefits
- • Reliable ketosis by hour 16–18
- • Strong growth-hormone response
- • Simpler day — one big meal plus a smaller second
Risks & cautions
- • Easy to under-eat protein and calories — track for the first 2 weeks
- • Hunger and irritability are common until adapted
- • Not appropriate for people with eating-disorder history
- • Athletes with high training volume may need a longer window on heavy days
Frequently asked questions
Is 20:4 sustainable long-term?
How is 20:4 different from OMAD?
Will I lose muscle on 20:4?
Can I do 20:4 every day?
Related schedules
Track your 20:4 fast in QoFast
Live timer, milestone tracking, water and electrolyte logging — free on iOS & Android.
