What is the OMAD Diet Plan? Exploring One Meal a Day Fasting

December 8, 2025 •

4 min read

According to a 2022 study, individuals eating within a two-hour window in the evening experienced significant fat and total weight loss compared to a standard eating pattern. The One Meal a Day (OMAD) diet leverages this principle of extreme time-restricted eating, but its strict nature comes with specific benefits and considerations.

Quick Summary

The OMAD diet is an extreme intermittent fasting method involving a 23-hour fast and a single daily meal within a brief window, used for potential weight loss and metabolic health benefits, though risks exist.

Key Points

What it is: OMAD, or One Meal a Day, involves fasting for 23 hours and consuming all daily calories in a single, one-hour eating window.
Weight Loss: The diet creates a significant calorie deficit, forcing the body to burn stored fat for energy, leading to weight loss.
Risks: Major concerns include nutrient deficiencies, potential muscle loss, extreme hunger, fatigue, and unsustainable long-term adherence.
Getting Started: It is recommended to transition gradually from less extreme fasting schedules, like 16:8 or 20:4, to help your body adapt.
Nutrient Focus: The single meal must be nutrient-dense, containing a balance of proteins, healthy fats, and carbohydrates to avoid deficiencies.
Medical Caution: The diet is not suitable for everyone and requires consultation with a healthcare provider, especially for those with pre-existing conditions.

What is the OMAD Diet Plan?

The One Meal a Day (OMAD) diet is a highly restrictive form of intermittent fasting where you consume all your daily calories and nutrients within a single, condensed eating window, typically lasting around one hour. This leaves the remaining 23 hours of the day for fasting, during which only zero-calorie beverages like water, black coffee, and unsweetened tea are permitted. The core premise is that by drastically limiting the eating period, you naturally reduce your overall caloric intake, forcing the body to burn stored fat for energy.

How does OMAD work?

The mechanism behind OMAD is rooted in metabolic changes that occur during extended fasting periods.

Metabolic Switching: After roughly 12 to 17 hours of fasting, your body depletes its readily available glucose stores and switches to burning stored body fat for energy. This process is often referred to as entering a state of ketosis.
Hormonal Changes: Fasting leads to a significant drop in insulin levels. Lower insulin facilitates the burning of fat for fuel. Fasting can also increase the production of human growth hormone (HGH), which helps preserve lean muscle mass during weight loss.
Calorie Deficit: By eating only one meal, it can be challenging to consume enough calories to prevent a deficit. This makes weight loss a more passive process, as calorie counting is often unnecessary to achieve a lower overall intake.

Potential benefits of the OMAD diet

For some individuals, OMAD offers distinct advantages:

Simplifies Eating: With only one meal to plan, prepare, and clean up, OMAD can save a significant amount of time and effort.
Enhanced Focus: Many adherents report experiencing improved mental clarity and increased focus during their fasted state, potentially due to the release of certain hormones like norepinephrine.
Improved Insulin Sensitivity: Extended fasting periods give the body a break from constantly processing glucose, which can improve insulin sensitivity and help regulate blood sugar levels.
Autophagy: Longer fasting windows may stimulate autophagy, a process where the body cleans out old, damaged cells, promoting cellular repair and renewal.

Risks and considerations of the OMAD diet

Despite its potential benefits, the OMAD diet is not without significant drawbacks and risks. As an extreme form of fasting, it is not suitable for everyone and requires careful consideration and medical supervision.

Nutrient Deficiencies: Consuming all nutritional requirements in one meal is extremely difficult, potentially leading to deficiencies in essential vitamins, minerals, and fiber over time.
Fatigue and Irritability: Especially during the initial adjustment phase, many people experience fatigue, dizziness, headaches, and low energy levels as their body adapts to burning fat instead of glucose.
Binge Eating Risk: The intense hunger from a 23-hour fast can lead to overeating or unhealthy food choices during the single meal, potentially negating the benefits or leading to binge-eating patterns.
Sustainability: The restrictive nature of OMAD means it is not a sustainable long-term solution for most people. Many studies show high dropout rates.
Impact on Blood Pressure and Cholesterol: Some studies have linked eating only one meal a day to higher LDL ("bad") cholesterol and increased blood pressure in some individuals.
Muscle Loss: Inadequate protein intake combined with infrequent eating can lead to a loss of lean muscle mass, which can negatively impact metabolism.

How to safely start the OMAD diet

If you decide to try OMAD, a gradual approach is key to help your body adapt and minimize side effects.

Start Gradually: Do not jump directly into OMAD. Begin with a less extreme form of intermittent fasting, such as the 16:8 method (fasting for 16 hours, eating for 8) or 20:4, to build your fasting tolerance.
Plan a Nutrient-Dense Meal: Make your single meal as nutritionally complete as possible. It should be rich in lean protein, healthy fats, complex carbohydrates, and plenty of vegetables to ensure you meet your daily needs.
Stay Hydrated: Drink plenty of water throughout the fasting period. You can also have black coffee or herbal tea.
Consider Electrolytes: Extended fasting can deplete electrolytes. Adding a pinch of sea salt to your water or using a zero-calorie electrolyte supplement can help prevent symptoms like headaches and fatigue.
Listen to Your Body: Pay close attention to how you feel. If you experience severe fatigue, mood swings, or other negative symptoms, OMAD may not be right for you.

Comparison of OMAD with other fasting methods


Feature	OMAD (23:1)	16:8 Method	5:2 Diet
Eating Window	One hour	Eight hours	Five days with normal eating; two days of calorie restriction
Fasting Period	23 hours	16 hours	24 hours on fasting days
Flexibility	Highly rigid; social challenges	Moderately flexible; fits most lifestyles	High flexibility; choose any two non-consecutive days
Intensity	Extreme	Beginner-friendly	Moderate
Meal Frequency	One large meal daily	Multiple meals within 8-hour window	Normal meals 5 days; restricted meals 2 days
Adaptation	Requires significant adaptation period	Easier to adapt to for beginners	Simple to start for many individuals

Conclusion

The OMAD diet plan is a highly restrictive and intense form of intermittent fasting that can offer benefits like weight loss and simplified meal planning due to a built-in calorie deficit. However, the extreme nature of eating all your food within a single hour comes with significant risks, including nutrient deficiencies, muscle loss, and a high potential for unsustainability. For most people, less restrictive forms of fasting, like the 16:8 method, offer similar metabolic benefits with fewer downsides. Anyone considering the OMAD diet should approach it with caution, start slowly, and ensure their single meal is packed with nutrient-dense foods. As with any major dietary change, consulting a healthcare professional is strongly recommended to determine if OMAD is safe and appropriate for your individual needs. For more information on intermittent fasting and its various approaches, see this resource from the Cleveland Clinic.

Frequently Asked Questions

No, OMAD is not safe for everyone. It is not recommended for pregnant or breastfeeding women, children, teenagers, older adults, or individuals with a history of disordered eating or underlying medical conditions like diabetes.

Yes, it is possible to lose weight on the OMAD diet. The restrictive eating window naturally creates a calorie deficit for many people, which is the primary mechanism for weight loss.

Your one meal should be as nutritionally complete as possible, including a balance of lean protein, healthy fats, complex carbohydrates, and plenty of fiber from fruits and vegetables to prevent nutrient deficiencies.

During the fasting window, you can drink calorie-free beverages such as water, black coffee, and unsweetened tea. Avoiding drinks with calories or artificial sweeteners helps maintain the fasted state.

Common side effects include extreme hunger, fatigue, low energy, dizziness, headaches, and irritability, particularly during the initial adjustment phase.

There is not enough research to confirm the long-term safety of OMAD, and most health professionals do not recommend it as a sustainable long-term strategy. Many practitioners use it for short periods, such as a few weeks or months, or cycle on and off.

You can exercise, but timing and intensity matter. Many people find it beneficial to work out 1-2 hours before their eating window to optimize nutrient absorption. It is important to listen to your body and adjust intensity based on energy levels.

OMAD is the most extreme version of intermittent fasting with a very short eating window. Other methods like 16:8 or 5:2 are less restrictive and may be more sustainable for most people.