Key Takeaways

• The One Meal A Day (OMAD) diet is a form of intermittent fasting that involves consuming just one meal a day, typically within a 2-hour window, and fasting for 22 hours.

• There is limited research on the OMAD diet. As it is extremely restrictive which can lead to nutritional deficiencies and binge eating, it is not a recommended way of eating to manage weight and chronic disease.

Intermittent fasting (IF) has become popular due to the potential benefits of weight loss and improvement in health markers (e.g. blood pressure, blood glucose levels, inflammation) and gut microbiota composition.

During intermittent fasting, calorie counting is not needed as the shortened eating window generally results in lower calorie consumption over the course of the day, making it an attractive way of eating for weight loss.  

Research looking at the effects of intermittent fasting during Ramadan also found improvements in blood cholesterol levels, blood pressure and blood glucose levels.

Time-restricted feeding (TRF) is one form of intermittent fasting where people shorten the eating window to less than 12 hours a day. A popular TRF regime is the 16:8 regime, where you fast for 16 hours and consume all your meals within an 8-hour period.

In a non-fasted state (e.g. after meals), glucose is the main energy source for the body. After about 12 hours of fasting, glucose stores are depleted and the body switches to using fat stores for energy, potentially inducing fat loss which is associated with reduced insulin resistance and other health benefits.

The One Meal a Day (OMAD) diet has a 22:2 regime, which consists of consuming just one meal a day, typically within a 2 hour window, and fasting for 22 hours.

But does a longer fasting period actually lead to increased health benefits?

What does research say about the One Meal a Day (OMAD) diet?

Unlike its other time-restricted feeding counterparts, there is limited data on the health impact of the OMAD diet.

There was a small study with 11 participants below the age of 35, all of whom were healthy lean individuals. For 11 days, participants consumed the calories needed to maintain their body weight in either three meals per day (breakfast, lunch and dinner) or one meal per day (between 5pm and 7pm). This was followed by a 2-week break period before participants went on the other diet (three meals per day or one meal per day) for another 11 days. The study found weight loss and reduction in fat mass in the group that consumed one meal a day, with no impact on their strength or aerobic capacity. Lower blood glucose levels during the later part of the day was also seen in the one meal a day intervention.

Despite the seemingly positive outcomes, it is important to note that the study was done in a small population of young, healthy lean individuals, and over a short period of time.

In another study that ran the intervention over a longer period of 8 weeks, the one day a meal intervention resulted in a worsening of blood pressure and blood cholesterol levels despite reductions in fat mass. Participants on the one meal a day intervention also reported a significant increase in hunger levels. The study was done on healthy, middle-aged adults (40-50 years) who were within the healthy weight range.

Furthermore, a large study of more than 24,000 US adults aged 40 years and older found a higher risk of death, including death specifically from cardiovascular disease, in those consuming one meal a day compared to those consuming three meals a day.

Potential Risks and Considerations

The OMAD diet has not been proven safe and is not recommended as a healthy way of eating. There are risks associated with the OMAD diet which would likely outweigh any benefit you may get from it:

• Nutritional deficiencies: It is unlikely to be able to meet your daily nutritional requirements with only one meal. For example, to meet the daily nutritional requirements of a 70kg male, he would have to consume 3 chicken breasts, 2 cups of cooked vegetables, 2 bowls of rice, and 2 portions of fruit in a single meal. This may be doable but unlikely enjoyable. Having such a large meal in one sitting could also cause bloating and abdominal discomfort. To add to that, we need to include a variety of foods in our meals to get different vitamins and minerals which would not be feasible or practical when having just one meal a day.

• Hunger and cravings: The long fasting period could induce extreme hunger. Some people find themselves constantly thinking about food and their next meal which can significantly affect their quality of life. People with a history of binge eating / preoccupation of food / emotional eating may also have the habit triggered by this extreme form of intermittent fasting.

• Impact on social life: Many of our social activities involve food and eating one meal a day may mean that you miss out on the enjoyment of some of these events because you’re supposed to be fasting.

• Overly restrictive and unsustainable: The extremely restrictive nature of the OMAD diet makes it unsustainable for the long-term.

It is understandable that with different lifestyles, schedules and priorities, meal planning and calorie counting can be difficult. Maybe there are some days where you only have time for one meal. In this case, the 5:2 diet (another form of intermittent fasting) could be an option for you. You can read more about the different types of intermittent fasting here.

There are many ways of healthy eating as everybody is different and circumstances are unique to each person. Some people feel good while intermittent fasting, some don’t. And that is ok. The body thrives on consistency (just like how we feel and perform better on a regular sleep schedule) so finding a way of eating that is sustainable for you is your best bet. Work with your dietitian to formulate a meal plan that works for you.

Unlike intermittent fasting, NOVI Optimum doesn't require a complete overhaul of your dietary habits overnight. Instead, you'll get personalized, step-by-step guidance on how you could make tiny tweaks to your current lifestyle habits—from food choices to exercise regimen—for big, sustainable weight loss results.