OMAD Diet: Is Eating One Meal a Day Safe and Effective for Weight Loss?

If you’re on the search for a diet to help you meet your health goals, it’s likely that someone you know — a cousin, a friend, or a neighbor — has told you that they do intermittent fasting (IF).

There are many ways to do IF, but the general idea is that you’ll set strict periods of time in which you don’t eat, and eat as you normally would while not fasting. You might choose to do alternate-day fasting and eat every other day. You might choose an “eating window” each day, and fast outside of that window. You might fast for two days a week and eat normally for the other five, in an approach called “5:2 fasting.”

Now there’s a new type of fasting gaining steam: the OMAD, or “one meal a day,” diet. Simply put, the idea of the OMAD diet is you consume all of your daily calories and nutrients during one meal each day. It may sound straightforward enough, but registered dietitian nutritionists have some concerns about the approach.

On the OMAD diet, you’ll fast except for when you’re eating that single daily meal.

“Overall, it’s a time-restricted, calorie-restricted diet,” explains Amy Shapiro, a registered dietitian in private practice at Real Nutrition in New York City.

Generally speaking, OMAD is an extreme version of fasting, says Lisa Moskovitz, RDN, CEO of NY Nutrition Group. For that reason, she adds, “some experts may argue that consuming just one meal a day is unnecessary in order to get the benefits of fasting.”

There are a couple of ways people may follow the OMAD diet, Shapiro says: They may eat one meal a day, or choose a short eating window in which they consume one meal and limited snacks per day.

But she adds that it’s not recommended to practice OMAD every day, and so some people will practice a less extreme version of IF the other days of the week. For example, someone may do OMAD one to several days per week, and then follow a 16/8 IF schedule (where they fast for 16 hours and eat for 8 hours) for the rest of the week.

In this sense, doing OMAD combined with another IF approach would be more flexible than, say, the ketogenic diet, a strict high-fat, low-carb plan.

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

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, says Moskovitz.

Shapiro also advises that 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, adds Moskovitz. “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. This diet requires you to eat a lot of food at one time, which may cause GI discomfort.

Still, many people who are not in these categories will decide to move ahead with OMAD — and if you’re one of these individuals, know that careful planning is key. “If you’re going to attempt it, you still have to make sure you’re doing your best to eat balanced and nutritiously and make sure you’re still eating enough calories for the day if you want to stay healthy,” advises Moskovitz. “Fasting alone won’t be beneficial if [you’re] not carefully constructing the meals you’re eating in that time frame.”

Always speak to your doctor before starting a new diet, especially if you’re managing an underlying health condition or taking medication, or if OMAD represents a dramatic change in the way you eat.

If you are interested in trying OMAD but have not yet tried other types of IF, start slowly, suggests Shapiro. “Start with a 12-hour fast and then build up to 14 or 16 hours. Then try OMAD for a few days once you have eased your body into it,” she explains.

The single meal you eat on OMAD may contain anywhere from 1,500 to 2,500 calories or more, depending on your body weight, size, and health goals, says Moskovitz. She cautions that it shouldn’t contain less than 1,200 calories: “Eating this way is not an excuse to undereat.” (At the same time, however, it’s worth noting that it can be difficult and uncomfortable to eat a whole day’s worth of food in one sitting.)

Here are two ways your day might look — one in which you’re following a traditional healthy diet, and one following Moskovitz’s suggestions for a balanced OMAD meal:

Traditional Balanced Diet

Breakfast: Oatmeal with berries and walnuts

Lunch: Leafy greens topped with quinoa, roasted vegetables, avocado, and chickpeas and drizzled with a vinaigrette

Snack:  Baby carrots and red pepper strips and hummus

Dinner: Piece of salmon served with broccolini and farro

Dessert: Dark chocolate

OMAD

One meal, lunch example:

• 1 turkey sandwich with 2 full-sized slices of bread, 4 slices of turkey, 2 slices of cheese, ½ avocado, lettuce, and tomato
• 2 hard-boiled eggs
• 1 banana
• 1/3–½ cup of trail mix
• 1 smoothie with 1 cup of veggies, 1 cup of berries, 2 tablespoons (tbsp) of almond butter, 4 ounces (oz) of yogurt, 1/3rd cup raw oats, and almond milk base
• 1 oz of dark chocolate

One meal, dinner example:

• 6–8 oz of fish, chicken, turkey, or tofu
• 2 cups of cooked whole grain/starch (rice, pasta, or potatoes)
• 2 cups of cooked veggies
• 2 tbsp of olive oil
• 2 oz cheese or ½ avocado
• 1 cup of fresh fruit
• 1 cup of Greek yogurt + 1/3 cup chopped nuts

There’s a lack of research on the health effects of consuming one meal a day specifically. However, emerging research on IF provides some clues about the potential benefits of this type of diet.

However, there are important caveats to these conclusions. The authors point out that there are no large, randomized controlled trials that look at how IF patterns affect cardiovascular disease. They conclude that more research is needed, especially when it comes to what specific IF regimen is best and how long it’s necessary to follow IF for these benefits.

Moskovitz advises that you do not need to fast to garner these types of health benefits. It’s possible to reap these benefits with a traditional healthy eating plan with three meals per day.

Moreover, Shapiro says that some people may actually see the opposite occur: Their blood sugar and cholesterol may instead increase on OMAD if they’re filling their one meal a day with unhealthy foods, such as lots of processed food, fast food, and added sugar. If you are going to start OMAD, she recommends having a blood test taken before starting and then again three months later, which will provide a personalized picture of how your body is responding.

If done correctly, you may lose weight on OMAD. “You’ll see weight loss due to calorie restriction, healthier food choices, and proper energy usage,” says Shapiro.

But losing weight on OMAD isn’t a given. “If you eat the wrong food and eat unhealthy junk food during your eating window instead of nutritious foods, this can be very unhealthy.”

As noted, individuals who are pregnant or nursing, under 18, take insulin to manage diabetes, have a past eating disorder, or who take food-dependent medication should not follow OMAD. If you have diabetes, Moskovitz advises speaking with your doctor before starting OMAD, as one large meal per day may lead to an unhealthy blood sugar spike.

While, anecdotally, some people note that they have better gastrointestinal function on OMAD, others notice the exact opposite. With so much in your stomach at once, it’s likely that not everything will get broken down or digested properly, says Moskovitz. In the time after eating this supersized meal, you may not feel well.

Also, you may find that your hunger level can get out of control as you wait to eat your one daily meal. That, in itself, can lead to overeating and cravings for less healthy foods during your meal. Moreover, you may assume you can eat whatever you want in this one meal or eating window. But that’s not the case, especially if you’re doing OMAD with the goal of promoting your health.

If you’re committed to trying IF, consider allowing yourself a wider eating window. “Many people see great results with time-restricted eating with windows of 12 to 16 hours of fasting because it limits additional calorie intake while allowing your body to burn its own fat for fuel, and allows for balanced meals,” says Shapiro.

During this type of IF, you are still able to eat several times a day, so you’ll have more opportunity to get in the calories and nutrients you need.

Other popular varieties of IF with wider eating windows than OMAD include:

• 5:2 fasting, where you’ll eat normally for five days and then fast (or eat very few calories) for two
• Overnight fasting, where you’ll stop eating after dinner and resume eating at breakfast the next morning (at least 12 hours later)
• Alternate-day fasting, where you’ll alternate fasting and non-fasting days

Learn More About Other Types of IF

Eating an OMAD diet may be an on-trend way to do IF, but it’s not a surefire way to achieve your health goals or improve health problems. What’s more important is that you are listening to your body’s needs. “Find a way of eating that works for you,” says Moskovitz. “Make sure it fits within your lifestyle. If OMAD makes you feel great, keep going, but make sure you’re doing it as healthily as possible.”