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Last updated: February 21, 2026
Intermittent fasting structures when you eat, not what you eat. By compressing your eating into a defined window, most people naturally consume fewer calories without tracking every meal. This guide covers all nine major IF protocols, their expected results, and how to choose the right one for your lifestyle.
| Protocol | Window | Difficulty | Est. Weekly Deficit |
|---|---|---|---|
| 12:12 Fast | 12h fast / 12h eating | beginner | 400 cal |
| 14:10 Fast | 14h fast / 10h eating | beginner | 600 cal |
| 16:8 Fast | 16h fast / 8h eating | intermediate | 850 cal |
| 18:6 Fast | 18h fast / 6h eating | intermediate | 1,050 cal |
| 20:4 Fast (Warrior Diet) | 20h fast / 4h eating | advanced | 1,200 cal |
| OMAD | 23h fast / 1h eating | advanced | 1,350 cal |
| 5:2 Diet | 2 restricted days / 5 normal days | intermediate | 1,100 cal |
| 24-Hour Fast | 24h fast 1-2x per week | advanced | 2,200 cal |
| Alternate Day Fasting | 2 restricted days / 5 normal days | advanced | 2,000 cal |
The easiest entry point to intermittent fasting. Matches your natural sleep cycle.
A gentle step up from 12:12. Easier to maintain than 16:8 but more effective.
The most popular IF protocol in the world. Fast 16 hours, eat in an 8-hour window.
A step beyond 16:8. More aggressive fat loss with a tighter eating window.
One large meal per day in a 4-hour window. The Warrior Diet approach.
One meal a day. The most extreme daily fasting protocol.
Eat normally five days a week. Restrict to 500 calories on two non-consecutive days.
One or two full 24-hour fasts per week. Maximum periodic calorie reduction.
Fast every other day. The most aggressive structured fasting protocol.
One large meal per day in a 4-hour window. The Warrior Diet approach.
One meal a day. The most extreme daily fasting protocol.
One or two full 24-hour fasts per week. Maximum periodic calorie reduction.
Fast every other day. The most aggressive structured fasting protocol.
Intermittent fasting works primarily through calorie reduction. Compressing your eating into a defined window makes it harder to overeat. Most people eat 10 to 20 percent fewer calories when following a structured fasting protocol compared to unstructured eating, without consciously tracking anything.
Secondary mechanisms include improvements in insulin sensitivity (lower fasting insulin), increased fat oxidation during fasting periods, and reduced exposure to the hormones that drive hunger throughout the day (ghrelin adapts to new meal timing within two to three weeks). These mechanisms are real but smaller than the direct calorie reduction effect.
The most important variable for IF success is adherence. The best protocol is the one you can sustain. For most people, starting with 14:10 or 16:8 and staying consistent for four to eight weeks produces better results than attempting OMAD or alternate day fasting and burning out in two weeks.
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