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A Guide to the OMAD Diet

OMAD, which stands for ‘‘one meal a day,’’ is a type of intermittent fasting in which you consume all of your daily calories in one meal or in a very short time window. You fast for the rest of the time.

Intermittent fasting (IF) has emerged in popularity as research has unveiled its health and weight management benefits. Simply put, IF is eating in a specific time window and fasting for the remaining time. OMAD is a more strict version of IF that involves fasting for up to 23 hours and consuming all food over a 1–2 hour period. It does not specify when or what you eat.

This article provides an overview of the OMAD diet. It also discusses the benefits and risks of the diet.

What is the OMAD diet? The OMAD diet is a form of IF where you essentially consume all of your calories for the day in one meal or over a 1-2 hour period.

You fast for the remaining time, which is about 22–23 hours, including while you sleep. Many people do this by skipping breakfast and eating their meal in the middle of the day or in the early evening. You can consume noncaloric beverages, such as water, black coffee, unsweetened tea, and apple cider vinegar, during the fasting window. OMAD is a popular dietary approach for weight management. Some people may also do it for mental clarity or various other health reasons. It also simplifies your diet.

How does the OMAD diet work?

Fasting for an extended period and eating one meal a day is a way of influencing how your body uses energy. The OMAD diet forces your body to rely on fat and sugar stores for fuel. It can also help train your body to be more “metabolically flexible,” which means that your body can efficiently alternate between using fat or sugar as fuel, depending on what is available. Some research suggests that OMAD may promote weight loss because you are eating fewer calories overall. A 2021 meta-analysis reviewed 17 randomized clinical trials that investigated the effects of IF versus a calorie-restricted diet on various anthropometric parameters. The researchers concluded that IF had comparable effects to calorie restriction on weight loss. Similarly, a 2021 randomized control trial reported that IF and a calorie-restricted diet had comparable effects on reducing blood pressure, hemoglobin A1C, and blood lipids for participants with obesity. Both groups also experienced reductions in body fat. However, the IF diet was significantly lower in calories than the calorie-restricted diet, providing 500–600 calories a day rather than 1,000–1,200.

What are the benefits of the OMAD diet?

Studies have shown fasting to have numerous health benefits. However, it is worth noting that most of the research on fasting is not specific to the OMAD approach.

  • Autophagy: Research suggests that fasting activates autophagy, your body’s clean-up mechanism for dysfunctional cells, toxins, and waste products. Autophagy also occurs in neurons of your brain, which likely explains why animal studies have shown IF to combat age-related neurological disorders such as Alzheimer’s disease and Parkinson’s disease.

  • Genetics and cellular health: In animal studies, researchers have demonstrated that fasting can turn on genes that slow aging, turn off genes that promote aging, and make your cells more resilient to stressors. It can also activate and regenerate stem cells.

  • Cardiovascular health and inflammation: A 2019 randomized controlled trial reported that alternate day fasting (ADF) improved cardiovascular markers, reduced fat mass and inflammation, and had beneficial effects on several markers involved in aging.

  • Weight loss: A 2021 review concludes that IF appears to be a safe and effective strategy for weight loss while having beneficial effects on several markers of metabolic health in those who have obesity.

What are the risks of the OMAD diet?

The OMAD diet has several risks to consider. People may be able to get the benefits of fasting by adopting a less strict dietary regimen.

  • Lacking nutrients: Consuming only one meal a day or limiting your eating window to 1-2 hours makes it difficult to obtain all of the nutrients you need. In addition, there is only so much nutrition your body can absorb at one time, so this approach to eating may limit your body’s absorption of nutrients from your meal.

  • Blood sugar spike: It can be stressful to the body or cause a major blood sugar spike if you try to pack an excessive amount of food into one sitting rather than spacing it out.

  • Loss of muscle: It can also be easy to lose muscle if you are only eating one meal a day. Your body can absorb a limited amount of protein at once. Spacing your intake of protein out in intervals is more likely to produce the best results for increasing or maintaining lean muscle mass. Losing muscle mass can slow down your metabolism.

Some people should avoid OMAD and other restrictive forms of fasting. These individuals include:

  • children

  • people who are pregnant or lactating

  • people who have a history of an eating disorder

  • older adults

  • people with certain medical conditions, such as hypoglycemia

  • people who take insulin to manage diabetes

  • people who take food-dependent medication

There may be other people for whom OMAD is not safe. It is best to check with a doctor before making any significant changes to your diet. What foods do you eat on the OMAD diet? The OMAD diet plan does not specify what foods to eat. However, it is important to make your one meal count by opting for more nutritious foods. You also need to make sure that you are getting adequate protein and some healthy fats. If you do try the OMAD diet, you can get a well-rounded array of nutrients by:

  • Consuming a variety of colorful vegetables: Try steaming them lightly to help break down the cellulose in the vegetables, which helps you digest them better.

  • Opting for unprocessed meats: Try to avoid fatty cuts of meat or processed meats.

  • Choose healthy fats: Choose foods rich in omega-3 fatty acids, such as salmon, chia seeds, and walnuts.

Additionally, it is best to include some monounsaturated fats, which are in avocados and olives. Fats will also help you absorb the fat-soluble vitamins A, D, E, and K. Visit our hub to read more about food, nutrition, and diet. What foods do you avoid on the OMAD diet? Technically, no foods are off-limits on the OMAD diet. However, you may wish to limit highly processed foods with low nutritional value. You may also want to be mindful of your sugar intake to avoid having a major blood sugar spike. Other types of OMAD diet The OMAD diet is a version of IF. There are also several other forms of IF. Time-restricted eating, which involves limiting food intake to a specific time window, is a popular version. The more common variations are 16:8 and 18:6, where you fast for 16 or 18 hours and eat in an 8- or 6-hour window. Time-restricted eating emphasizes eating during the hours that are optimal for your circadian rhythm. Another IF option is alternate-day fasting, which gives people the flexibility to eat normally for a day and then fast or restrict their calorie intake the next day. Other forms of IF may involve fasting or significant calorie restriction for 1–2 days per week. Summary The OMAD diet is an extreme form of intermittent fasting in which you eat all of your food for the day in a 1–2-hour period. As you are fasting for 22–23 hours, this theoretically forces your body to draw energy from its reserves, such as stored fat and glycogen, for fuel. Although numerous studies have demonstrated several health benefits of fasting, most of them are not specific to the OMAD diet. Therefore, it may not be necessary to undergo such an extreme form of fasting to reap the health benefits. There are also many possible risks involved with following the OMAD diet, especially if you do so for a long time. Another option could be to use the OMAD approach once in a while instead of every day. There is not much research on the safety and benefits of the OMAD diet. It is best to speak with a doctor before trying it or making any other significant changes to your diet. — Written By Jenna Sager, MS, RDN

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