About half of adults in the U.S. have attempted weight loss in the past year. The One Meal a Day (OMAD) trend, also called the 23:1 intermittent fast, is a form of fasting that has gained attention in the health and fitness communities and has risen in popularity among social media platforms.
But is this diet healthy and effective, particularly in the long term? This article explores the effects, benefits, and drawbacks of eating just one meal daily as part of the OMAD diet plan.
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What Is One Meal a Day (OMAD)?
As the name implies, the OMAD (one meal a day) diet consists of eating one meal daily (within one hour) and fasting the remainder of the day, which means you’ll fast for 23 hours. You must consume the food on a standard dinner plate, and your food pile must not rise above 3 inches from the plate. However, you can eat whatever you want during the one-hour window.
You can drink water, black coffee, unsweetened tea, or other calorie-free beverages for the remainder of the day.
Different approaches and variations in meal timing and diet composition exist when following the OMAD diet. However, the general approach remains the same. Many people following this diet eat dinner as their one meal and fast the rest of the day.
Other forms of intermittent fasting are less restrictive than the OMAD diet plan. For example, some fasters eat a healthy diet five days weekly and consume very few calories the remaining two days. Others eat only during a four-hour or eight-hour window instead of a one-hour window — or they fast every other day.
The Science Behind OMAD
OMAD dieting fits into a broader category of intermittent fasting. Studies demonstrate the benefits (and drawbacks) of this type of fasting.
Researchers found that intermittent fasting can improve overall health and well-being by promoting:
- Calorie reduction
- Reduced body fat
- Weight loss
- Improved insulin sensitivity and metabolic flexibility
- Reduced heart disease risk factors
- Lower systemic inflammation
- Reduced blood sugar
- Improvements in lipid profiles
- Healthier blood pressure
However, the researchers suggest that study subjects also experienced reduced bone density and less lean body mass due to intermittent fasting.
Intermittent fasting may also affect hormones, including ghrelin, leptin, growth hormone, and sex hormones. For example, studies show it could decrease testosterone levels but may improve symptoms of polycystic ovary syndrome (PCOS) in women.
Researchers found that fasting increased ghrelin (the hunger hormone) decreased energy expenditure, reduced leptin (the fullness hormone), and led to a 5-fold increase in growth hormone.
Potential Benefits of OMAD
The potential benefits of following the OMAD diet include:
Weight Loss and Fat Reduction
The OMAD typically reduces total calorie intake because it’s difficult to consume a lot of daily calories when eating just one meal. Reducing your calorie intake to create a deficit is one of the best ways to lose weight and increase fat burning.
Improved Insulin Sensitivity
Weight loss can improve insulin sensitivity in overweight and obese individuals. Studies show that intermittent fasting decreases body mass index (BMI), body weight, waist circumference, total cholesterol, low-density lipoprotein (LDL), triglycerides, insulin resistance, and blood sugar.
Enhanced Mental Clarity and Focus
Fasting also appears to affect brain functioning. Researchers suggest that metabolic changes associated with fasting may enhance brain function, improve cognitive performance, increase adaptability, and increase resistance to injury and disease.
Simplified Meal Planning
Another potential perk of the OMAD diet is that it’s convenient. It reduces the time needed for meal preparation. You only need to cook once a day, which is advantageous if you don’t love food prep.
Autophagy and Cellular Repair
Fasting also plays a role in cellular maintenance and longevity. Researchers found that intermittent fasting and calorie restriction increase cell longevity, extend the cell lifespan, and support anti-aging. However, the same study suggests that prolonged excessive calorie restriction may harm cells, increasing the risk of cellular death.
Potential Drawbacks and Risks
Despite the numerous potential benefits of the OMAD diet, it’s not for everybody. Examples of drawbacks and risks include:
Nutrient Deficiencies
Severely restricting calories during the OMAD diet makes it difficult to meet daily nutritional needs, including protein, carbohydrates, fat, fiber, vitamin, and mineral requirements. Consuming too few calories can cause nutrient deficiencies that negatively affect your energy levels, hair, skin, nails, bone health, and lean body mass.
Overeating and Digestive Issues
Fasting for 23 hours before mealtime increases the risk of consuming excessive food in one sitting (overeating). This can cause bloating or other digestive issues.
Impact on Energy Levels and Physical Performance
Highly restrictive diets, including the OMAD, can lead to reduced physical stamina, diminished athletic performance, and fatigue.
Social and Lifestyle Constraints
Following the OMAD diet means you may have to fast during social gatherings and not eat at dinner parties, restaurant meet-ups, weddings, work outings, and other social events. For this reason, the OMAD diet can be socially difficult to adhere to.
Physical and Mental Health Considerations
The OMAD diet is challenging for many people to maintain, particularly in the long term. It may increase your risk of developing an unhealthy relationship with food. Fasting for long periods also increases the risk of irritability, anxiety, headaches, lightheadedness, hunger, weakness, insomnia, loss of lean muscle, and nausea.
Who Can Benefit from OMAD?
Suitable candidates for the OMAD include those desiring weight loss and metabolic health improvements, such as lower cholesterol, blood sugar, and blood pressure. However, caution should be used when adopting the OMAD diet indefinitely because of the potential negative effects of long-term use, including nutrient deficiencies.
Individuals who should avoid OMAD include pregnant and nursing women, babies, children, teenagers, athletes, people with diabetes or other chronic conditions, and individuals taking medications affected by food — such as insulin.
It’s highly important to consult with a healthcare professional before beginning the OMAD plan or other weight loss diets to determine if they’re safe and effective.
How to Implement OMAD Safely
Ways to complement the OMAD diet in the safest manner possible include:
Gradual Transition
Rather than beginning the OMAD diet in its entirety, gradually ease into this eating pattern to help your body become accustomed to it. Doing so may lessen the severity of potential side effects.
Meal Composition and Nutrient Density
When eating just one meal daily, it’s vital to ensure balance by choosing nutrient-dense foods. Choose an array of heart-healthy fats, protein, fiber-rich plant foods, and vitamin and mineral supplements as directed by a healthcare provider.
Drink plenty of water and avoid highly processed junk foods (sweets, sugary drinks, processed meats, refined grains, added sugar, etc.) with a low nutritional value.
Hydration and Electrolyte Balance
Dehydration and electrolyte imbalance are concerns when fasting for long periods. Drink water often throughout the day (urine should be light yellow or clear). Hydration needs are about 16 cups of fluids daily for men and about 12 cups per day for women.
Consume plenty of electrolytes to avoid imbalances. Consider adding electrolyte powders to your water or use electrolyte tablets. However, avoid electrolyte drinks or other products containing artificial sweeteners (aspartame, saccharin, sucralose, etc.) that may negatively affect the fasted state.
Listening to Your Body
It’s critical to listen to your body during intermittent fasting and recognize signs of overconsumption or nutrient deficiencies. See a healthcare provider to undergo nutrient testing to detect and correct any deficiencies. If the OMAD diet is too restrictive, consider other types of fasts or simply adopt a well-balanced meal plan like the Mediterranean diet or plant-based diet.
Comparing OMAD to Other Fasting Methods
In addition to OMAD, other forms of intermittent fasting include:
16/8 Method
The 16/8 fast involves eating during an eight-hour window each day and fasting the remaining 16 hours. It’s typical to eat only between 10:00 a.m. and 6:00 p.m. Studies suggest this diet is the most common intermittent fast and is linked to reductions in body weight, fat mass, and calorie intake with improvements in insulin resistance.
The 16/8 diet produces similar health benefits as the OMAD plan, but it’s often easier to adhere to because it’s less restrictive.
5:2 Diet
The 5:2 diet is another type of fasting that's similar to OMAD. However, this meal plan allows you to eat a typical healthy diet five days a week and fast by eating just 200-600 calories daily the other two days. However, ensure your two fasting days are non-consecutive (avoid fasting more than 24 hours in a row).
This type of fast is less restrictive than the OMAD. However, studies demonstrate that adherence to the 5:2 eating pattern is initially high but declines over time. It did enhance weight loss and received favorable ratings from study subjects who followed the diet for one year.
Alternate-Day Fasting
As the name implies, alternate-day fasting involves fasting every other day. Limit your calories to 500 or about 25% of your typical daily intake during fasting days. You can eat whatever you’d like during non-fasting days, but choosing a well-balanced meal plan is highly beneficial.
Studies suggest that alternate-day fasting for 6 months (followed by a 6-month maintenance phase) led to weight loss and increased HDL cholesterol. However, LDL cholesterol also increased, participant dropout rates were high, and this diet wasn’t more effective than non-fasted, reduced-calorie eating patterns.
Eat: Stop: Eat
The eat:stop:eat fasting method involves complete fasting (not eating at all) for 24 hours once or twice each week. While this type of fast might help you shed pounds, it can also cause more extreme side effects, such as headaches, hunger, irritability, and fatigue.
Practical Tips for Success with OMAD
Practical tips for success when following the OMAD diet for weight loss or health improvements include:
Meal Planning and Preparation
Strategies for creating balanced meals include:
- Fill your plate half full of fruits and non-starchy vegetables.
- Fill the other half of the plate with lean protein foods (fish, chicken, eggs, etc.) plus whole grains, legumes, or starchy vegetables.
- Add olive oil or other plant oils, avocados, nuts, seeds, nut butter, and additional heart-healthy (plant) fats.
- Add in dairy foods or calcium-rich plant-based alternatives.
Drink water, black coffee, or unsweet tea throughout the day and mix in electrolytes as needed to maintain balance while fasting.
Managing Hunger and Cravings
Drinking water, black coffee, unsweetened tea, or unsweetened sparkling water can help manage hunger and cravings during OMAD fasting periods. If necessary, consume a less-restrictive form of the OMAD diet or gradually ease into this meal plan to minimize hunger, fatigue, nausea, and other potential side effects.
Staying Motivated and Consistent
Making lifestyle adjustments is key to staying motivated and consistent when following the OMAD diet. If the diet isn't right for you, keep a journal, establish a routine, stay in contact with a healthcare provider, and consider other healthy meal plans.
Common Myths and Misconceptions
There are common myths and misconceptions associated with the OMAD diet, including unrealistic fears and exaggerated benefits. While the OMAD diet offers benefits for weight loss and chronic disease risks, it’s not a magic weight loss or health bullet.
OMAD is difficult to adhere to for many individuals, particularly long-term. However, it can be beneficial to eat well-balanced meals and take multivitamins or other dietary supplements to prevent nutritional deficiencies.
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Key Takeaways
- The OMAD diet consists of fasting for 23 hours daily and eating one large meal within one hour, often at dinner.
- OMAD dieting offers potential benefits, including weight loss, fat loss, smaller waist, longevity, enhanced mental clarity, and improvements in insulin resistance, cholesterol, blood pressure, triglycerides, and other disease risk factors.
- However, OMAD can be difficult to adhere to, and it may cause fatigue, decreased sports performance, nutrient deficiencies, irritability, lightheadedness, anxiety, hunger, headaches, muscle loss, nausea, bloating, weakness, or overeating at mealtime. OMAD can also alter hormone levels.
- Children, teenagers, pregnant and nursing women, athletes, people with chronic diseases, and those taking certain medications should not follow the OMAD diet.
- There are less restrictive forms of intermittent fasting available to choose from. Examples include eating only during an 8-hour period (16:8 method) and following a typical diet five days per week while consuming very few calories for two (5:2 fast).
- It’s vital to make informed decisions when choosing a weight loss diet, including the OMAD fast, and consult with a healthcare professional before trying it — particularly if you have a medical condition or take medications or supplements.
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