OMAD, aka the OMAD diet or the “one-meal-a-day diet”—is a dieting strategy that involves eating one meal a day.

Some people believe that eating once a day is capable of improving your metabolic health, helping you avoid disease and dysfunction, and even making you live longer, and they provide all manner of sciency-sounding rationes for how this works.

Others, however, are less convinced, and question the OMAD diet’s efficacy, safety, and practicality.

If you want to know exactly what OMAD fasting is and whether or not you should try it, this article is for you.

In it, you’ll learn everything you need to know about OMAD, including answers to questions like . . .

  • What is OMAD?
  • What are OMAD benefits?
  • What are OMAD downsides?
  • Who should follow the OMAD diet?
  • What are some examples of OMAD meals?

What Is the OMAD Diet?

OMAD is an initialism for “one meal a day,” and it refers to a diet in which you consume all of your daily calories within one hour (normally in one large meal) and spend the other 23 hours of the day fasting.

There are no calorie targets or macronutrient guidelines—you can eat as many calories as you want, from whichever foods you like—the only stipulation is you must eat your meal at roughly the same time each day. 

For most people, eating once a day is easiest if they eat in the evening, so they choose to have their one-hour eating window at some point between the hours of 6 p.m. and 10 p.m.

However, if you prefer to eat a large breakfast, you could choose to have your eating window earlier in the day—between the hours of 7 a.m. and 11 a.m., for example.

In addition to eating one meal a day, some versions of the OMAD diet allow you to eat a small snack or two during your OMAD fasting window. 

OMAD purists would advise against this, however, and instead only allow themselves to consume water and zero-calorie drinks like black coffee or tea during their fasts. 

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OMAD Benefits

The most common OMAD benefits you hear bandied around the Internet include . . .

However, when you take a closer look at the studies used to support these claims, you quickly realize they’re a little hard to swallow.

For example, there’s no research that looks at the OMAD diet specifically. The studies that OMAD adherents use to bolster their claims all involved different kinds of fasting protocols, and there’s no way to know if the benefits associated with one can be applied to the other.

What’s more, much of the research on fasting is done on animals, and we can’t assume humans would experience the same benefits as rats do when they go for extended periods without eating.

One thing eating one meal a day has been shown to be effective for, however, is weight loss . . .

OMAD and Weight Loss

The only way to lose weight is to eat fewer calories than you burn, also referred to as eating in a calorie deficit. 

Several studies show that diets that involve fasting are effective at helping you lose weight. The main reason for this is it’s easier to eat in a calorie deficit when you eat fewer meals each day.

Research shows that the “one meal a day diet” is no different.

In one study conducted by scientists at the Beltsville Human Nutrition Research Center, participants who could only eat one meal per day couldn’t consume enough calories in a single sitting to meet their daily calorie needs.

As you’d expect, they lost an average of around four pounds (two kilograms) of fat over the course of the eight-week study.

This isn’t to say that fasting diets are inherently better than more traditional forms of dieting, though.

In fact, a large review conducted by scientists at The University of Sydney analyzed 40 studies on intermittent fasting (with 12 comparing it directly to traditional dieting methods), and found no significant benefits related to body composition, fat loss, insulin sensitivity, or hormones.

OMAD Downsides

Just because eating one meal a day will help you lose weight doesn’t mean it’s good for your health.

Let’s take a look at some of the downsides associated with the OMAD diet and why you might want to think twice about using it to lose weight.

1. It probably isn’t optimal for building muscle.

If you want to build muscle, you need to maintain a mild calorie surplus.

That is, you need to eat about 110% of your total daily energy expenditure (TDEE) every day. The reason for this is a calorie surplus optimizes your body’s “muscle-building machinery,” so to speak, greatly enhancing your body’s ability to recover from and positively adapt to resistance training.

(And if you’d like specific advice about how many calories, how much of each macronutrient, and which foods you should eat to build muscle, take the Legion Diet Quiz.)

However, as we’ve already seen, when you eat just 1 meal a day it can be difficult to consume enough calories to maintain your weight, let alone build muscle. 

That’s not all, though. 

If you want to build muscle, you also have to eat enough protein—around 0.8-to-1 gram of protein per pound of body weight per day, to be precise.

Not only is it difficult to eat that amount of protein in a single meal, it’s probably not optimal for muscle growth, either.

The best available research shows that splitting up your daily protein intake across 3-to-6 meals is superior to eating the same amount of protein in fewer sittings, as this is more effective for keeping muscle protein synthesis elevated throughout the day.

By fasting for most of the day, you’re missing out on several opportunities to boost muscle growth, and you’ll likely gain less muscle over time as a result. 

2. It can lead to extreme hunger.

An obvious problem with eating less is increased hunger.

Studies shows that many people who limit themselves to eating fewer meals each day experience an extreme level of hunger that carries with it numerous unwanted side effects such as:

  • Dizziness 
  • Nausea
  • Anger
  • Lethargy
  • Constipation

Not only does extreme hunger make the process of dieting miserable in the short term, it makes it less likely that you’ll adhere to the protocol long term (which is perhaps why studies that involve fasting have higher drop-out rates than other human-feeding studies).

3. It probably isn’t optimal for health.

Eating one meal a day probably isn’t optimal for your health because . . .

  • It’s difficult to eat enough of the vitamins and minerals your body needs to stay healthy when you severely restrict the amount of food you eat. (This is particularly true if you eat fewer fruits and vegetables, which is often the case with people who follow the OMAD diet).
  • Research shows that eating just once a day is linked to increased blood pressure and cholesterol.
  • You can become so hungry during your fasting periods that when it comes time to eat you binge on high-calorie, unhealthy foods.
  • Alternating between long fasts and binge eating may promote disordered eating in susceptible people.
  • Restricting calories while also eating inadequate protein causes muscle loss.
  • Research shows that eating 2-to-3 meals per day provides several health benefits over eating one meal a day.
  • If you stuff yourself in the evening, you may be uncomfortably full when it’s time to go to bed, thus interfering with your sleep.

Who Should Follow the OMAD Diet?

There’s little evidence that the OMAD diet offers any health or weight loss benefits over more conservative dieting approaches such as flexible dieting, IIFYM, or intermittent fasting.

It also tends to be harder to stick to than most other diets, so if you’re looking for a long-term dieting solution, OMAD probably isn’t for you.

Whether or not you should follow the OMAD diet largely boils down to your personal preferences and whether or not eating fewer meals throughout the day fits better with your lifestyle.

If you currently follow a fasting diet such as the Warrior Diet, Leangains, or Eat Stop Eat, and want to see how you’d fare eating even fewer meals each day, you may want to give OMAD a try.

Likewise, if you’re the type of person who enjoys tinkering with different dieting strategies, it won’t hurt to give OMAD a go for a week or two. 

Lastly, the OMAD diet might work well if you have a particularly busy schedule and struggle to find time during the day to sit down and enjoy a meal. 

For instance, if you’re a shift worker that never eats at “conventional” meal times, or if you’re a college professor that tends not to break for a meal during the working day, the OMAD diet might be a more enjoyable way to consume your daily calories. 

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Examples of OMAD Meals

When you only eat one meal a day, it’s difficult to provide your body with enough of the nutrients it needs to thrive unless you plan everything ahead of time.

That’s why it’s important to put together an OMAD meal plan before you commit to this style of dieting.

Some OMAD pendants say your entire meal should fit on one plate, but to them I say poppycock.

In my opinion you should aim to eat meals that . . .

  • Contain at least 1,200 calories
  • Are as nutrient-dense as possible
  • Are as high-protein as possible
  • Include a side dish and a dessert

Here are some sample OMAD meals that you can try:

OMAD Meal #1:

Main: Lamb of Gains

Side: Bacon-Wrapped Maple-Glazed Carrots

Dessert: Healthy Raspberry Ice Cream

OMAD Meal #2:

Main: Beef, Bean & Cheese Burritos

Side: Broccoli & Cheese Twice-Baked Potatoes

Dessert: Cookies & Cream Protein Bars

OMAD Meal #3:

Main: Creamy Chicken Marsala Pasta

Side: Saucy Green Beans & Sausage

Dessert: Mini Chocolate Cream Cakes

+ Scientific References