OMAD (One Meal a Day) — Schedule, Risks, and Safer Alternatives
What OMAD involves, why it is not a beginner protocol, who should avoid it, and how to step down from shorter fasting windows.
Published: 2026-06-21
OMAD — One Meal a Day — means taking all daily calories in one meal, usually inside a one-hour window. On the timer this is closest to 23:1: 23 hours fasting, 1 hour eating. OMAD-specific research is thinner than the research on shorter protocols such as 16:8, so this page treats it as an advanced schedule, not a default goal.
The short version: do not use OMAD as your first fast. Test a shorter window first and stop if the schedule pushes you toward rushed eating, dizziness, or obsessive restriction.
What an OMAD schedule typically looks like
On an OMAD schedule, you pick a one-hour eating window — common choices are a lunchtime window (e.g., noon–1 PM) or an evening window (e.g., 6–7 PM). Outside that window, only zero-calorie drinks are consumed: water, black coffee, and plain tea. The remaining 23 hours constitute the fast. Some practitioners allow the window to extend to two hours, making it a 22:2 fast in practice. Use the fasting calculator to plan your OMAD schedule and eating window times.
A safer step-down path
- Start with 16:8 until the fasting window feels routine rather than forced.
- Try 18:6 if two meals in a 6-hour window still lets you eat calmly and adequately.
- Only then consider 20:4, where meal planning starts to matter much more.
- Treat OMAD/23:1 as optional. If it makes meals rushed or social life brittle, a wider window is the better fit.
Who OMAD may suit
- Experienced intermittent fasters who have consistently practised 16:8 or 18:6 and want to extend their fasting window further.
- People who naturally prefer eating one large meal and find multiple smaller meals less satisfying or convenient.
- Those without the medical contraindications listed below and who have discussed extended fasting with a clinician.
Who should approach OMAD with extra caution
OMAD is not appropriate for beginners to fasting, and is contraindicated for many groups. In particular, the following groups should consult a clinician before attempting OMAD or avoid it entirely:
- People new to fasting — 16:8 or 18:6 is a more appropriate starting point.
- People with a history of disordered eating. Severe restriction can exacerbate unhealthy patterns and OMAD has been flagged in the literature as potentially problematic in this context.
- People with type 1 or type 2 diabetes, or who take insulin or glucose-lowering medication. A 23-hour fast creates substantial blood sugar management challenges that require medical oversight.
- People who are pregnant, breastfeeding, or trying to conceive.
- Children and adolescents under 18.
- People who are underweight or who have recently recovered from an eating disorder.
Practical tips for OMAD
- Prioritise nutrient density. Fitting all daily nutrients into one meal requires careful planning. Aim for protein (to support muscle), fibre (to support digestion and satiety), healthy fats, and micronutrient-rich vegetables. A dietitian consultation may be helpful.
- Hydrate and manage electrolytes. With a 23-hour fasting window, sodium, potassium, and magnesium losses may be more pronounced. Water with electrolytes (zero-calorie formulations) throughout the day can help.
- Don't begin OMAD abruptly. Stepping down through 16:8, then 18:6, then 20:4 before trying OMAD is typically more sustainable and reduces the severity of adjustment symptoms.
- Monitor how you feel. Persistent fatigue, poor concentration, dizziness, or mood changes that do not improve after two weeks are signs that OMAD may not be the right approach for you.
- Consider sustainability. Research suggests that adherence over time is one of the strongest predictors of outcomes with any dietary pattern. A protocol you can maintain comfortably for months is typically more beneficial than a more extreme one maintained for days.