What Is Intermittent Fasting?
Intermittent fasting (IF) is an eating pattern that cycles between periods of eating and periods of fasting on a set schedule. Unlike traditional diets, IF does not specify which foods to eat — it specifies when to eat them. The most common protocols are named after the fasting-to-eating hour split: 16:8 means 16 hours of fasting followed by an 8-hour eating window each day.
IF itself does not directly cause weight loss. It works by making it easier for many people to naturally eat within a calorie deficit, since the eating window is shorter and there are fewer opportunities to snack. If you are using IF for weight loss, pair it with a personalised target from our Calorie Deficit Calculator.
How to Calculate Your Eating Window
Enter the time you plan to eat your first meal of the day, then choose a protocol. The calculator subtracts your fasting hours from 24 to find your eating window length, then adds that to your first meal time to find your last meal time — the point at which your next fasting period begins.
Common Intermittent Fasting Protocols
| Protocol | Fasting / Eating | Notes |
|---|---|---|
| 14:10 | 14h / 10h | Easiest entry point for beginners |
| 16:8 | 16h / 8h | Most researched and widely used protocol |
| 18:6 | 18h / 6h | Tighter window, harder to hit protein goals |
| 20:4 | 20h / 4h | Warrior Diet style, one large meal window |
| OMAD | 23h / 1h | One meal a day — hardest to meet nutrient needs |
Tips for Success With Intermittent Fasting
- Start with 14:10 or 16:8 and extend the window gradually rather than jumping straight to OMAD.
- Water, black coffee, and plain tea do not break a fast for most protocols.
- Hit your protein target within your eating window to preserve muscle mass.
- Shift your window earlier or later gradually if it conflicts with training or social schedules — sudden large shifts disrupt sleep.
- IF is not appropriate during pregnancy, breastfeeding, or with a history of disordered eating — check with a healthcare provider first.
Scientific basis: de Cabo R, Mattson MP. "Effects of Intermittent Fasting on Health, Aging, and Disease." N Engl J Med. 2019;381:2541–2551.
For more on how meal timing fits into your overall calorie and diet strategy, see our Calorie & Diet Planning Guide.