Comparing the main protocols
The 16:8 protocol (16 hours fasting, 8 hours eating) has the largest evidence base and the highest adherence rates. It is well-suited to people who skip breakfast or eat dinner early. The 18:6 and 20:4 protocols increase the fasting duration, which some research associates with greater metabolic benefits but also reduced adherence over time. The 20:4 protocol — sometimes called OMAD (one meal a day) — requires careful meal planning to meet micronutrient needs within a single eating window.
The 5:2 protocol involves two non-consecutive fast days per week with 500–600 kcal (rather than zero), with normal eating on the remaining five days. It is appealing for people who find daily time restriction difficult. Alternate-day fasting has the broadest evidence base for metabolic outcomes but is the most demanding to maintain long-term.