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The one meal a day diet — or OMAD diet — involves eating your daily calories in a single meal.
Proponents of the diet claim it can promote fat loss, reduce inflammation, and improve other markers of health, similar to other forms of time-restricted eating.
However, the OMAD diet carries several downsides and is not appropriate for some people.
This article explains the benefits and downsides of the OMAD diet and provides sample meals.
What is the OMAD diet?
The OMAD diet is a strict form of intermittent fasting that involves fasting for 23 hours and eating for about one hour — for this reason, it’s also known as the 23/1 diet.
However, the time frame isn’t that important, only that you have one meal during the day.
Most people choose to have their one meal at the same time each day, usually for dinner.
No food is off limit and only calorie-free drinks like water, black coffee, or unsweetened tea are allowed outside of the meal or during the fast.
How long you follow the OMAD diet is up to you — some people follow it several days a week, cycling it with a typical three-meal-a-day routine, whereas others have fully adapted the diet.
Some people set daily calorie goals but most people don’t count calories when following the OMAD diet.
Weight loss as a potential benefit
The benefits of intermittent fasting related to things like autophagy and inflammation tend to be exaggerated and extrapolated to humans from animal studies.
However, the most consistent benefit associated with intermittent fasting regimes like the OMAD diet is weight loss.
In one study, healthy participants ate their calories in one meal daily for eight weeks. After an 11 week washout period, the same participants then ate their calories across three meals each day (1).
Despite the participants consuming about the same number of calories, the participants lost significantly more body fat than when they ate their calories in one meal per day instead of three.
However, the loss in weight was not significant compared with their starting weights.
A different study, this time a review of 22 randomized control trials, ranked the OMAD diet as the best meal frequency for reducing body weight, but with low certainty (2).
Based on the current research, there is no strong evidence of a metabolic benefit to the OMAD diet that promotes weight loss, but it can promote weight loss in some people by helping them create and maintain a calorie deficit (3).
But of course, not everyone will eat fewer calories with the OMAD diet.
Although the OMAD diet may help some people lose weight by eating fewer calories, there are several downsides to the diet.
Potential side effects
The OMAD diet — like other forms of intermittent fasting — may cause unwanted side effects.
While these side effects are relatively minor and don’t occur in everyone, they are important to be aware of.
Common side effects of the OMAD diet include (x):
- low energy
- feeling cold
Likely unsustainable and impracticable
As you can imagine, trying to eat a day’s worth of calories in one meal can be a challenge.
It can also be difficult to incorporate eating OMAD into your daily life if you frequently travel, take clients out to dinner, or have other responsibilities that could interfere.
Consequently, the OMAD diet can be very difficult to follow long-term and therefore experience any sustainable weight loss benefits.
Likely nutritionally inadequate
Even when carefully planned, it can be difficult to get the nutrients you need in adequate amounts by eating OMAD.
Especially considering that nutrient-dense foods like fruits, vegetables, whole grains, and lean meats are very filling due to their high fiber and protein content.
As such, taking a basic multivitamin/mineral supplement like this one is a good idea to ensure you’re getting enough nutrients.
Not appropriate for people with certain conditions
The OMAD diet is not for everyone, especially if you have diabetes.
In one study, healthy participants experienced higher fasting blood sugar and insulin resistance when they consumed their daily calorie needs in one but not three meals for eight weeks (3).
Compared with three meals, eating OMAD has also been shown to raise blood pressure and elevate liver enzymes, something to consider if you have high blood pressure or a condition that affects the liver like fatty liver or liver cirrhosis (1).
Foods to eat and avoid
The OMAD diet is intended to reduce your daily calorie intake since it can be difficult to meet your daily calorie needs in one meal.
However, your meal should contain at least 1,200 calories and be as nutrient-dense as possible.
Here are some nutrient-dense foods to eat:
- fruits, such as apples, berries, and oranges
- vegetables, such as arugula, broccoli, mushrooms, and zucchini
- starchy vegetables, such as acorn squash, green peas, potatoes
- whole grains, such as brown rice, oatmeal, and quinoa
- proteins, such as beans, nuts, meats, poultry, seafood, and seeds
- dairy, such as Greek yogurt, cottage cheese, and milk
- healthy oils, such as olive and avocado oil
Limit highly processed foods like:
- chocolate and candies
- ice cream and frozen desserts
- frozen entrees like pasta dishes and pizza
- baked goods like muffins, cakes, and pastries
- processed meats like bacon, sausages, and deli meats
- sugary drinks like soda or specialty coffee drinks
You will likely have to eat to the point of mild discomfort to ensure you’re getting enough calories.
Here are some nutritional complete meal ideas:
- No dietary restrictions: burrito made with rice, black beans, ground beef, guacamole, shredded lettuce and cheese, and salsa, followed by a quinoa salad.
- Lacto-ovo vegetarian: stir-fry made with fresh ramen noodles mushrooms, scallions, bok choy, carrot, an egg, and a ginger garlic sauce, followed by Greek yogurt topped with berries and slivered almonds.
- Vegan: tofu bowl made with tofu, rice, garlic, radishes, kale, chard, and an almond butter sauce, followed by a garbanzo bean salad.
With large enough portions, these meals easily exceed 1,200 calories.
The bottom line
The OMAD diet is a strict form of intermittent fasting that involves eating one meal a day.
The OMAD diet can help you lose weight, but only if it helps you create and maintain a calorie deficit.
Unfortunately, the diet is associated with some side effects like bloating and hunger, can be nutritionally inadequate, and be difficult to follow long-term.
Certain conditions like diabetes, high blood pressure, or gastroparesis also don’t lend themselves well to the diet.
In either case, if you wish to try the OMAD diet, make sure your meal contains at least 1,200 calories and consists primarily of nutrient-dense foods.