The One-Meal-A-Day (OMAD) diet is an extreme version of time-restricted eating. In the OMAD protocol, individuals consume all their daily calories within a single, one- to two-hour eating window, followed by a 22-23 hour fast. While colloquially grouped under the umbrella of "intermittent fasting," the scientific community often reserves that term for diets involving more drastic caloric restriction over multiple days. OMAD represents the most advanced form of intermittent fasting, offering benefits like simplified eating, potential weight loss, and improved metabolic health.
Understanding Time-Restricted Eating
It's important to distinguish between "intermittent fasting" and "time-restricted eating." The term “intermittent fasting” to diets that drastically restrict calories for 2-4 days of the week (such as not eating at all for a day, or eating very few calories for a couple days of the week). For daily fasting of set durations, the term “time-restricted eating” is preferred. Time-restricted eating is often described as the ratio of hours spent abstaining from food and the hours where eating is permitted.
The 18:6, 20:4, and one-meal-a-day (OMAD) protocols are types of time-restricted eating where you abstain from eating for 18 to 23 hours, and then eat freely for the rest of the day. Those who follow the OMAD protocol eat all their food at one sitting, which typically lasts an hour or less, while the other protocols typically involve more than one meal or a meal and a snack.
Potential Benefits of OMAD
Proponents of OMAD claim it can bring impressive health benefits, such as:
- Simplified Meal Planning: OMAD eliminates decision fatigue around food choices and meal planning. With OMAD, there is no need to plan multiple meals throughout the day.
- Potential Weight Loss: The naturally restricted eating window makes it difficult to consume excess calories, creating an automatic calorie deficit, which can lead to weight loss. Eating just one meal a day reduces calorie intake compared to consuming three meals, leading to effective and rapid weight loss. Study participants who tried eating one meal a day ended up with less total body fat.
- Improved Metabolic Flexibility: Most of the purported benefits of fasting come from the shift into an energy-scarce state, which upregulates metabolic pathways associated with cell-cycle regulation and energy mobilization. Shorter fasts probably don’t provoke these changes, but fasting for 18 hours or more might. In adult men with prediabetes and obesity, a 6-hour period of eating followed by 18 hours of fasting improved their blood sugar levels.
- Increased concentration and productivity: Since the one-meal-a-day diet does not include lunch, it can eliminate the sluggishness of the body when digesting food for lunch.
- May help you to burn fat.
Risks and Side Effects of OMAD
While OMAD offers potential benefits, it's crucial to acknowledge the risks and potential side effects:
Read also: One Meal a Day Keto
- Nutritional Deficiencies: Meeting all micronutrient needs in a single meal proves extremely difficult. Research shows it carries risks including elevated blood pressure, higher cholesterol levels, and potential nutritional deficiencies. The extreme nature makes it challenging to maintain adequate nutrition and a healthy relationship with food.
- Elevated Blood Pressure and Cholesterol: Eating one meal a day can increase your blood pressure and cholesterol.
- Muscle Loss: Failing to consume adequate protein (100-130g) can lead to muscle loss.
- Hormonal Imbalances: Women's bodies respond differently to fasting due to hormonal differences. Extended fasting can affect reproductive hormones. Hormonal fluctuations during these phases may make OMAD more challenging.
- Menstrual Cycle Changes: Extended fasting can affect reproductive hormones.
- Potential Risks of Fasting: Shakiness or physical weakness, intense hunger or binge eating, fatigue and low energy levels, brain fog or difficulty concentrating.
- High Dropout Rates: Studies have reported high rates of participant dropout, likely due to the challenge of adhering to such a limited eating window on a sustained basis. Intermittent fasting regimens like OMAD have a dropout rate of up to 65%. It’s no easier to follow than other calorie restriction plans.
- May Make You Hungrier: When you eat one meal a day rather than three, your body produces more of a hormone called ghrelin, which makes you feel hungry.
Who Should Avoid OMAD?
OMAD is not suitable for everyone. It is important to consult with a nutritionist for advice.
In general, OMAD is not a sustainable long-term diet and should not be used as a primary method for weight loss.
The OMAD diet can be extremely dangerous for children and young adults who are hypoglycemic, have diabetes, obesity, or metabolic disorders. Moreover, this diet can also increase the risk of binge eating.
Fasting can be contraindicated in some diseases such as type 1 diabetes, pregnancy, and preexisting eating disorders. If you already have concerns in either area, eating just once a day might not be safe.
Fasting of any type increases the risk of extremely low blood sugar, also known as hypoglycemia, in people who have Type 2 diabetes.
Read also: Combining Keto and OMAD
How to Implement OMAD Safely
If you're considering OMAD, here are some guidelines for a safer approach:
- Consult with a Healthcare Professional: Before starting any diet plan, you should consult with a nutrition expert for guidance. If attempting OMAD under medical supervision, start with short trials of 1-2 weeks to assess tolerance and monitor for adverse effects.
- Start Gradually: Jumping directly from three meals per day to OMAD often leads to failure.
- Prioritize Nutrient-Dense Foods: Your single 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. Just because you're eating once doesn't mean food quality doesn't matter. Attempting OMAD without meal planning often results in nutrient-poor choices.
- Ensure Adequate Calorie Intake: Your single meal typically needs to contain 1,500-2,000+ calories depending on your size and activity level.
- Stay Hydrated: Many people forget to drink enough water during fasting hours.
- Supplement Electrolytes: Extended fasting depletes sodium, potassium, and magnesium.
- Eat Mindfully: Take 45-60 minutes to eat your meal.
- Track Your Progress: Use a journal or app to monitor energy levels, hunger patterns, and physical changes.
- Have an Exit Strategy: Know when to modify or discontinue.
- Medical Supervision and Monitoring: If you do attempt OMAD, medical supervision and regular monitoring (including DEXA scans for body composition) are essential.
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.
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.
OMAD Rules
While OMAD doesn't have official "four rules," common guidelines include:
- Consume all daily calories within a 1-2 hour window.
- Fast for 22-23 hours daily with only zero-calorie beverages.
- Focus on nutrient-dense whole foods to maximize nutritional value.
- Stay properly hydrated throughout the fasting period.
What to Drink During the Fasting Window
During your 22-23 hour fasting window, you can drink water, black coffee (no cream or sweeteners), plain tea (green, black, or herbal), sparkling water, and zero-calorie electrolyte supplements. Avoid any beverages with calories, including bulletproof coffee (butter and MCT oil break the fast), protein shakes, juice, smoothies, and bone broth.
Read also: Beginner's Guide to OMAD
Expected Weight Loss on OMAD
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.
Personal Experience with OMAD
Joel Hunter, a lifestyle vlogger on YouTube, shared his experience with OMAD:
"Back in late 2022, I started doing intermittent fasting, where you fast for long periods of the day and only eat within certain hours. Specifically, I tried the OMAD-one meal a day-approach to intermittent fasting.
I'm a father of three and throughout the last decade, I have struggled to find a balance between my family life and responsibilities and my health.
I was always good at working out and fairly active but my problem wasn't the gym. It was the fridge.
At my low point, my weight ballooned out to an unhealthy 206lbs, which for a shorter guy is noticeably portly. I felt I was unhealthy and wanted to improve the situation for myself and to set an example for my family.
So my motivation was high, and I was very disciplined, especially in terms of snacking and what I ate during my eating windows. By the end, I had lost around 35lbs.
Along the way, I've learned a lot about hunger; specifically, how to control it. Much of it is really an emotional response. Often, we eat because we think we're hungry. While there are hormonal responses that trigger hunger and cravings, I believe much of it boils down to our psychology and mental strength.
I've found several methods to avoid hunger while fasting, which is a significant challenge that many fasters face. The key strategies include staying busy and active and ensuring meals are planned in advance. This planning is crucial to prevent constant thoughts about food throughout the day. It's particularly challenging when you're surrounded by food, such as during grocery shopping or in places where food is readily available. These situations can trigger hunger, so being prepared and having a plan is essential. If you're going out, planning your meal helps to avoid surprises that may trigger cravings or temptation.
Another key lesson I've learned during fasting is the necessity of being calorie-conscious and eating healthily. Many practice "dirty OMAD," where they eat fast food or whatever they feel like, and still lose weight. This is because they're achieving a caloric deficit. Fasting periods help in coaching the body to burn stored fat as well.
I'm not suggesting that "dirty OMAD" is inherently problematic. However, the issue with this approach is that it can be challenging to control the upper limit of calorie intake, especially with a longer eating window. The temptation to overeat is greater.
I believe the biggest reason I lost 35 pounds and then stalled at around that is my management of after-meal snacks that added sneaky calories. This is a common issue in many diets that can stall weight loss efforts and impact fasting. These include snacks like chocolate, chips, and others, which I often consumed after my main meal. Despite fasting every day, these snacks, especially during my four to six hour eating window at my laziest times, were significant.
Having those additional snacks contributed to the calories I needed to maintain my weight rather than lose more. So it's crucial to remain mindful of calorie intake even when you're fasting.
Now, I'm significantly lower than my starting point and comfortably at a weight where I don't need to overly focus on my diet or do additional exercise. The idea of having a cheat day or an off day doesn't really enter into my thoughts anymore. I know that I can eat this way and maintain a weight I'm comfortable with.
Would I like to be a little lighter and leaner? Yes, absolutely. But what I've learned from doing intermittent fasting is that it's a remarkably effective tool for further weight loss.
My goal for the next 12 months is to see how far I can take this weight loss and to get really serious about it.
In my early 20s, at what I call my "peak condition", it seemed effortless to sustain a healthy weight and athletic physique. I weighed around 165lbs, which is going to be my target weight, but I'm setting a realistic timeframe.
I plan to get there by losing a further 15 to 20lbs of fat in the next 365 days through my OMAD approach and keeping it off.
To achieve this, I will adopt a stricter approach to fasting this time, particularly in terms of consistency, to achieve greater results. I fasted for over a year, but there were some cheat days with shorter fasts. For example, I had breakfast on about 10 days.
I generally adhered well to the fasting regimen. But, moving forward, I plan to really focus on the quality of what I eat during my eating window, ensuring that my calories are from quality sources, primarily whole foods and protein.
That's how I had started. I initially focused on whole food sources and a high-protein diet, which led to my most significant success. Therefore, I plan to continue with this approach.
Overall, though, I was really satisfied with the weight loss achieved over the year."