The One Meal a Day (OMAD) diet is a form of intermittent fasting (IF) where you consume all your daily calories within a single, short eating window, typically lasting one to two hours, followed by a prolonged fasting period of 22-23 hours. While OMAD is considered an advanced intermittent fasting method, thousands of people successfully use this eating pattern to achieve their health goals, including weight loss and improved metabolic health. It is important to note that the scientific community often considers daily fasting of set durations as "time-restricted eating," with "intermittent fasting" reserved for diets with drastic calorie restriction for 2-4 days a week.
What is the OMAD Diet?
OMAD, or One Meal a Day, is a type of time-restricted eating where you abstain from eating for 18 to 23 hours, and then eat freely for the rest of the day. This means that you are fasting for the majority of the day, with only a short window of time to consume all of your daily calories.
How Does OMAD Work?
OMAD works by significantly extending the fasting period, which can lead to various metabolic changes in the body. The extended fasting period can lead to ketosis, a process where the body burns fat for fuel. Here's a breakdown:
- Fasting Period: For approximately 22-23 hours, you refrain from consuming any calories. During this time, you can drink water, black coffee, plain tea, sparkling water, and zero-calorie electrolyte supplements.
- Feeding Window: During your one to two-hour eating window, you consume your entire daily caloric intake.
Potential Benefits of OMAD
People who follow the OMAD diet believe that it offers numerous benefits, such as:
- Weight Loss: The naturally restricted eating window makes it difficult to consume excess calories, creating an automatic calorie deficit. Studies show variable results, but typical weight loss ranges from 4-10 pounds over 4-6 weeks. However, rapid initial weight loss often includes significant water weight. Sustainable fat loss rates of 1-2 pounds per week are realistic with proper implementation.
- Simplified Eating: OMAD eliminates the need for meal planning and preparation multiple times a day, and decision fatigue around food choices.
- Improved Metabolic Health: Fasting for extended periods can improve insulin sensitivity, reduce inflammation, and enhance metabolic health.
- Enhanced Mental Clarity: Many people report improved mental focus and clarity during fasting periods.
- Time Savings: By shrinking your eating period to 1 hour, you prepare food only once each day. You can spend those extra hours on other activities that help you reach your goals faster.
- Autophagy: Fasting triggers autophagy, a cellular process where the body cleans out damaged cells and regenerates new ones. Without autophagy, our cells would not survive or would grow abnormally, which would lead to various diseases.
- Metabolic Flexibility: OMAD can be used as a tool to improve your metabolic health and allows you to become more metabolically flexible during exercise without affecting your performance.
Potential Risks and Drawbacks of OMAD
The OMAD diet also carries some risks, and the extreme nature makes it challenging to maintain adequate nutrition and a healthy relationship with food. For example, on a daily basis, a person may:
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- Nutrient Deficiency: Meeting all micronutrient needs in a single meal proves extremely difficult and consuming all your nutrients in one meal can be challenging.
- Hunger and Cravings: Adjusting to OMAD can be difficult initially, with intense hunger and cravings during the fasting period.
- Social Implications: Eating only once a day can conflict with social events and family meals.
- Not for Everyone: OMAD may not be suitable for everyone, especially those with specific health conditions, pregnant or breastfeeding women, and individuals with a history of eating disorders.
- Elevated Blood Pressure and Cholesterol: Research shows OMAD carries risks including elevated blood pressure, higher cholesterol levels.
- Difficulty Concentrating: A person may have difficulty concentrating.
- Rebound Weight Gain: Rebound weight gain is a top concern.
- Increased Hunger: Increased hunger is a top concern.
- Nutritional Inadequacy: Nutritional inadequacy is a top concern.
- Disordered Eating: Following a restrictive diet may cause psychological distress, which may lead to disordered eating behaviors, including binge eating. Fasting all day and focusing on just one large meal may lead to binge eating and feeling a loss of control around food.
- Gastrointestinal Issues: This diet requires you to eat a lot of food at one time, which may cause GI discomfort. A possible drawback is diarrhea or loose, watery stools when breaking the fast.
Who Should Avoid OMAD?
Moreover, OMAD may actually be unsafe for certain groups of people. This includes people who are pregnant or nursing, who are younger than 18, and people who have an eating disorder or a history of disordered eating.
Another word of caution: If you take medication that must be consumed with food, reconsider OMAD. Not taking meds as prescribed could negatively affect absorbability and increase your risk of side effects. Examples of food-dependent medications include aspirin, certain NSAIDs, certain steroids, and allopurinol (Zyloprim).
People living with diabetes who are taking insulin should not follow this diet, as OMAD can affect blood sugar levels. In general, people with diabetes need to eat balanced meals regularly throughout the day. “Going prolonged periods of time without eating can lead to harmful blood sugar lows followed by subsequent highs once a larger meal is inevitably consumed,” she explains. “This pattern of inconsistent eating can make it difficult to keep blood sugar levels low and stable.”
Finally, if you often have gastrointestinal (GI) issues like bloating or an upset stomach, OMAD may not be a good fit for you.
How to Start OMAD Safely
Starting OMAD requires a strategic approach. Jumping directly from three meals per day to OMAD often leads to failure. If you are interested in trying OMAD but have not yet tried other types of IF, start slowly. Start with a 12-hour fast and then build up to 14 or 16 hours. Here are some tips for starting OMAD safely:
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- Start Gradually: Transition into OMAD by gradually increasing your fasting window. It’s a good idea to begin with a shorter fast, for example a 12-hour fast, so that your body can adjust. Remember that you do not have to go all in right away.
- Focus on Nutrient-Dense Foods: Ensure your one meal includes a variety of nutrient-dense foods.
- Stay Hydrated: Drink plenty of water throughout the day to stay hydrated and help manage hunger. The good news is that zero-calorie drinks are not off-limits. Hydration is vital for your energy levels and mental performance all day.
- Listen to Your Body: Pay attention to how your body responds to OMAD.
- Plan Your Meal: Plan and prepare your meal ahead of time to ensure it’s balanced and nutritious.
- Pick the Right Time: This depends on your schedule. For example, you can forgo breakfast and lunch, and break your OMAD fast at 6:00 pm if you work a typical 8-hour shift (from 9:00 am to 5:00 pm). It can be in the morning or evening when you can eat without distractions.
- Eat a Healthy Pre-Fast Meal: Consume foods high in vitamins and minerals that do not contain too many carbs. Limiting your carb intake before a fast will prevent filling your glycogen stores. Include proteins, healthy fats, and fiber.
- Keep Your Stress Levels Low: Being stressed out makes you hungry and crave foods that are high in sugar.
What to Eat on the OMAD Diet
An OMAD meal should be balanced and nutrient-dense, including 100-130g lean protein, healthy fats (avocado, nuts, olive oil), fiber-rich vegetables (25-35g fiber target), complex carbohydrates, and diverse whole foods to meet micronutrient needs. Your single meal typically needs to contain 1,500-2,000+ calories depending on your size and activity level.
Ready to try OMAD? Check out these meals to break your OMAD fast that pack nutrients. Feel free to change them (for example, if you would like to add fruit as a dessert) as long as they’re easy to digest and contain substantial amounts of fat and protein.
Here are some nutritionally complete meal ideas that are likely to exceed 1,200 calories if portion sizes are large enough:
- Baked chicken with mashed sweet potatoes topped with butter and roasted broccoli with olive oil, followed by full fat Greek yogurt topped with berries, nuts, seeds, and honey.
- Grilled salmon topped with guacamole, brown rice and black bean salad, and roasted plantains, followed by fruit served with nut butter, hemp seeds, and coconut flakes.
- Egg omelet with goat cheese, avocado, and grilled vegetables cooked in coconut oil, crispy baked potato wedges, followed by a side of fruit dipped in dark chocolate and whipped cream.
As you can see, each meal should account for all food groups and include: carbohydrates, fats, proteins. In a day, eating 1,200 calories is a general minimum. Most adults need much more than that to maintain their weight.
Building Muscle on OMAD
Building muscle on OMAD is challenging but possible with strategic planning. You need adequate protein (100-130g), proper training stimulus (2-3 strength sessions weekly), and timing your workout before your eating window. However, muscle growth will be slower compared to traditional eating patterns.
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For strength training or high-intensity workouts, schedule them 1-2 hours before your eating window to maximize post-workout nutrient absorption. Ensure your single meal contains adequate protein (100-130g) and carbohydrates to support recovery.
Common Mistakes to Avoid on OMAD
Just because you're eating once doesn't mean food quality doesn't matter. Failing to consume adequate protein (100-130g) can lead to muscle loss. Many people forget to drink enough water during fasting hours, and extended fasting depletes sodium, potassium, and magnesium. Attempting OMAD without meal planning often results in nutrient-poor choices.
OMAD and Women's Health
Women's bodies respond differently to fasting due to hormonal differences. Extended fasting can affect reproductive hormones. Hormonal fluctuations during perimenopause and menopause may make OMAD more challenging, and women have higher osteoporosis risk.
How Long Can You Safely Do OMAD?
Extended OMAD for 3 months can lead to both benefits and risks. Potential outcomes include 8-20 pounds of weight loss, improved insulin sensitivity, and metabolic adaptation. However, risks include nutritional deficiencies, metabolic disruptions, elevated blood pressure and cholesterol, and difficulty maintaining social eating patterns. Research on OMAD lasting 8+ weeks is limited, and most studies show high dropout rates.
If attempting OMAD under medical supervision, start with short trials of 1-2 weeks to assess tolerance and monitor for adverse effects. If you tolerate it well, you can extend to 4-6 weeks for specific goals. Extended use beyond 8-12 weeks requires careful medical monitoring due to risks of nutritional deficiencies and metabolic adaptations.
Monitoring Your Progress on OMAD
Ready to track your progress? Use a journal or app to monitor energy levels, hunger patterns, and physical changes. Have an exit strategy and know when to modify or discontinue.
OMAD: Is It Right for You?
OMAD can be healthy for some individuals when done properly with nutrient-dense meals and medical supervision. However, healthcare professionals generally recommend more moderate approaches due to concerns about nutritional deficiencies, blood pressure changes, and poor long-term adherence.
Overall, IF diets (including more extreme versions, like OMAD) are unlikely to cause harm to adults who are a healthy weight, overweight, or who have obesity, notes one review. But OMAD is a restrictive eating approach that won’t necessarily appeal to everyone. If you’re following OMAD, you’ll need to take care not to overeat or overindulge on unhealthy foods during your main meal. You may also struggle to fit an entire day’s caloric intake into one large meal - or find yourself feeling uncomfortably full after eating this much in one sitting. There’s also a lack of research on the long-term effects of OMAD.