The OMAD diet: benefits and risks

You may have heard that intermittent fasting comes with some health benefits, but what about eating just one meal per day? Here’s what you need to know about the OMAD diet and its potential benefits and risks.

The one meal a day diet (OMAD) is a type of intermittent fasting. Intermittent fasting is a way of eating that switches between periods of fasting and times you’re allowed to eat. With OMAD, you restrict all of your eating to one meal within one hour each day. 

The most common pattern used in intermittent fasting is a 16-hour window of fasting followed by an 8-hour “feeding” window (when you can eat). Another common type of intermittent fasting is alternating one complete day of fasting with one day of normal eating. 

OMAD is a stricter version, where you eat all of your daily calories within one meal in one hour, followed by 23 hours of fasting.

This diet recommends you have your one-hour meal period after the most active part of your day. 

OMAD, like most other forms of intermittent fasting, doesn’t restrict the types of food or drinks you can consume during your eating window. Even though there are no “off-limits” foods, most OMAD diet proponents encourage nutritious food choices like veggies, lean proteins, and whole grains. 

During the 23 hours of fasting, the diet allows water, coffee, and tea without any added cream or sugar. 

There are no daily calorie recommendations on the OMAD diet, likely because the time window limits how much food you can actually eat. However, if you follow this diet, you should still try to meet your body’s basic metabolic and caloric needs, accounting for the amount of caloric energy your body needs to function each day. 

Research shows the average woman needs around 2,000 calories per day to maintain her weight. The average man needs about 2,500 calories to maintain his body weight (Osilla, 2020). The number of calories you need will vary based on your height, weight, metabolism, and activity level.

Some people who follow an intermittent fasting diet plan combine it with other diets to guide food and calorie limits. It’s commonly paired with low-calorie, low-carb, and keto diets. 

There is very little research about following an OMAD diet, so it’s difficult to understand the benefits and risks of a 23-hour fasting eating pattern. Still, some research about the benefits of intermittent fasting in general may apply to the one meal a day diet plan. 

Here are some of the potential benefits of intermittent fasting:

Fat loss

Intermittent fasting may promote body fat loss and weight loss, so if that’s one of your goals, this may be a benefit (if however, you’re trying to maintain your current weight or gain weight, the OMAD diet may make it difficult to achieve those goals). 

After you eat, your body releases insulin to help bring glucose from your blood into your cells to either use as energy or store. When fasting, your blood sugar levels will slowly drop, and your body will switch to releasing hormones that bring energy out of storage. 

With intermittent fasting, some people claim the diet helps burn fat more than other eating patterns and helps reduce some of the risks associated with having obesity. 

Research shows people following intermittent fasting can lose between 1–13% of baseline weight. However, intermittent fasting appears no more effective than following other forms of caloric restriction (Welton, 2020). 

Better cholesterol levels

High-density lipoprotein (HDL) is called "good" cholesterol because it helps clean up "bad" cholesterols and triglycerides from the bloodstream, reducing the risk of cardiovascular disease. 

Some research shows intermittent fasting may increase HDL levels and lower LDL levels (Santos, 2018). However, other studies show that intermittent fasting produces no changes in HDL levels but does lower LDL and triglyceride levels (Meng, 2020). Whether or not HDL is increased, intermittent fasting may help lower your risk for heart disease by lowering LDL levels in your body.

Decreased inflammation

Chronic inflammation adds stress to your body and increases your risk for chronic diseases such as heart disease, atherosclerosis, and diabetes. Some research suggests regular fasting helps reduce systemic inflammation and stress resistance. This could help lower your risk of chronic illnesses (Paoli, 2019). 

Better blood sugar control

Following an intermittent fasting plan could help improve insulin sensitivity and blood sugar levels. When you spend less time eating throughout the day, your insulin levels have time to come down, and your body starts to bring energy out of storage. 

If you snack throughout the whole day, your cells are exposed to more sustained periods of raised insulin as it works to bring glucose into cells from the bloodstream. Some believe this could contribute to insulin resistance and that fasting could help prevent this. 

Research shows intermittent fasting can help reduce fasting glucose and fasting insulin levels. If you have diabetes, you'll want to work closely with your healthcare provider before starting an intermittent fasting diet. The changes in glucose and insulin that result might require close monitoring of your meal and medication plan (Albosta, 2021).

Few studies look at a 23 hour fast and 1-hour eating window, so the short and long-term risks are poorly understood. Some potential risks of following the OMAD diet include:

Increased blood pressure

One study found participants consuming just one meal per day had significant increases in their blood pressure levels (Stote, 2007). High blood pressure increases your risk for other conditions such as heart disease, stroke, and kidney disease. 

If you choose to follow the OMAD diet, have your blood pressure levels checked regularly for monitoring. 

Increased hunger

Only eating one large meal per day may leave you feeling hungrier and uncomfortable throughout the other 23 hours. In one study, when people ate one meal per day, they experienced more hunger and desire to eat, and feelings of fullness were significantly decreased (Stote, 2007). 

Low blood sugar

Fasting could lead to low blood sugar levels (hypoglycemia), especially in people with type 1 or type 2 diabetes who take medications to help lower blood sugar. Research shows any fasting increases the risk for hypoglycemic episodes in people taking diabetes medications for diabetes (Corley, 2018).

Symptoms of low blood sugar include:

• Fatigue

• Pale skin

• Shakiness

• Anxiety

• Sweating

• Irritability, confusion, or loss of consciousness

Digestive discomfort

Eating all of your calories in one meal may leave you feeling extremely full and uncomfortable. In one study where participants followed a one meal per day diet plan, participants reported extreme fullness, discomfort, and difficulty finishing their food in the allotted time (Stote, 2007). You may frequently go from feeling uncomfortably hungry to overfull following intermittent fasting.

Trouble meeting nutrition needs

It may be challenging to meet your calorie, protein, vitamin, and mineral needs when only eating for one hour of the day. Over time, not eating enough food can lead to muscle loss, nutrient deficiencies, and malnutrition. May promote disordered eating

Eating just one meal per day could promote eating disorder behaviors. Binge eating disorder is one such disorder, classified as eating excessive calories within a short window (Iqbal, 2021).

People who have a history of eating disorders should avoid an OMAD diet and talk with their healthcare provider or a dietitian to develop a healthy eating plan.

The best meal plan for you will depend on how you respond to food, and no one meal plan will work for everyone. Talk with your healthcare provider or a registered dietitian about any dietary changes you are considering to learn how they may affect your health. 

Overall, there is not enough research about eating just one meal per day for it to be recommended. There are both benefits and risks to following an intermittent fasting diet. The long-term effects of an OMAD diet are unknown, and it likely won’t be a sustainable way to eat for many people.

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Current version

July 19, 2021

Written by

Ashley Braun, RD, MPH

Fact checked by

Steve Silvestro, MD

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About the medical reviewer

Steve Silvestro, MD, Ro

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.