The main methods
16:8: fast for 16 hours, eat within an 8-hour window (most commonly skipping breakfast and eating between midday and 8pm). The most popular approach for daily practice. 18:6: more restrictive, 18 hours fasting. 5:2: eat normally five days, restrict to 500–600 calories on two non-consecutive days. Both produce similar metabolic benefits over time.
What happens in your body
After 12–14 hours without food, glycogen (stored glucose) depletes and the body switches to burning fat. Insulin levels drop significantly. Some research shows cellular repair (autophagy) increases. The subjective experience: hunger peaks around the 10–12 hour mark and often disappears — many people find they are genuinely not hungry at their usual breakfast time after 2–3 weeks.
Who it works for — and who should be cautious
IF is well-suited to people who prefer not eating breakfast, who find calorie counting tedious, and who want a simple rule rather than a complex diet. It is not appropriate for: pregnant or breastfeeding women, those with a history of disordered eating, people with type 1 diabetes or on insulin, or anyone underweight. Always check with a GP before starting if you have any health conditions.
Our picks compared
| Pick | Product | Best for | |
|---|---|---|---|
| Top pick | Dr Michael Mosley 5:2 fasting guide | 5:2 method | Check price → |
| Bottle | 1.5 litre water bottle time markings | Fasting hydration | Check price → |
| Tea | Herbal tea selection fasting friendly | Fasting drinks | Check price → |
| App | Fasting tracker app guide | Auto tracking | Check price → |
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