They are part of an ever-growing group of public figures touting the benefits of eating just one meal a day.
As a result, the one meal a day diet (OMAD) is the latest exciting weight loss trend. Proponents say it leads to rapid, long-term weight loss and better health, including delaying the aging process.
Like most weight loss programs, the OMAD diet makes big, bold promises. Here’s what you need to know about eating one meal a day and what it means for weight loss.
The OMAD diet explained
Essentially, the OMAD diet is a type of intermittent fasting, in which you fast for 23 hours and consume all of your daily calories in a single meal eaten within an hour.
The rules of the OMAD diet are presented as simple and easy to follow:
You can eat whatever you want, as long as it fits on a standard plate, with no calorie restrictions or nutritional guidelines to follow.
You can drink calorie-free drinks throughout the day (water, black tea and coffee).
You should follow a consistent eating schedule, eating your meal around the same time each day.
In addition to creating a calorie deficit, leading to weight loss, advocates believe that the OMAD diet’s extended fasting period causes physiological changes in the body that promote better health, including boosting your metabolism by triggering a process called ketosis, in which your body burns stored fat for energy instead of glucose.
What does the evidence say?
Unfortunately, research on the OMAD diet is limited. Most studies have examined its impact on animalsand the primary study with humans involved, 11 lean youngsters following the OMAD diet for just 11 days.
Claims about the OMAD diet are generally based on research on intermittent fasting, rather than the OMAD diet itself. There is evidence support the effectiveness of intermittent fasting to achieve weight loss. However, most studies have focused only on short-term results, typically considering results achieved over 12 weeks or less.
A longer-term study from 2022 139 obese patients were randomly assigned to either a low-calorie diet with time-restricted meals between 8:00 a.m. and 4:00 p.m. or a diet with daily calorie restriction only for 12 months.
After 12 months, both groups had lost about the same amount of weight and experienced similar changes in body fat, blood sugar, cholesterol and blood pressure. This indicates that the long-term weight loss achieved with intermittent fasting is not superior and comparable to that achieved by traditional dietary approaches (daily calorie restriction).
So, what are the problems with the OMAD diet?
1. It can lead to nutritional deficiencies and health problems
The OMAD diet’s lack of nutritional guidance on what to eat for one meal a day raises many red flags.
The meals we eat each day should include a balanced protein source with whole carbohydrates, vegetables, fruits, protein and good fats to support optimal health, disease prevention and weight management.
Not eating a balanced diet will lead to nutritional deficiencies which can lead to poor immune function, fatigue and decreased bone density, leading to osteoporosis.
Fasting 23 hours a day is also likely to lead to extreme hunger and uncontrollable cravings, which can mean you consistently eat foods that aren’t good for you at the time of eating.
2. It is unlikely to be sustainable
You may be able to stick with the OMAD diet at first, but it will ease off over time.
Extreme diets, especially those that prescribe prolonged periods of fasting, are not enjoyable, leading to feelings of deprivation and social isolation during meals. It’s hard enough to turn down a piece of birthday cake at the office, best case scenario, imagine how you’d feel when you haven’t eaten in 11 p.m.!
Restrictive eating can also lead to an unhealthy relationship with food, making it even more difficult to achieve and maintain a healthy weight.
3. Quick fixes don’t work
Like other popular intermittent fasting methods, the OMAD diet appeals because it is easy to digest and results appear quickly.
But the OMAD diet is just another fancy way to cut calories to get a quick drop on the scale.
As your weight decreases, things will quickly deteriorate when your the body activates its defense mechanisms to defend your weight loss. In fact, it will gain weight again – a response that stems from our hunter-gatherer ancestors’ need to survive periods of deprivation when food was scarce.
Despite the hype, the OMAD diet is not sustainable and does not lead to better weight loss results than its predecessors. Our old habits resurface and we find ourselves battling a cascade of physiological changes to ensure we gain back the weight we lost.
Successfully losing weight in the long term comes down to:
lose weight in small, manageable increments that you can maintain, especially periods of weight loss, followed by periods of weight maintenance, and so on, until you reach your goal weight
Make gradual changes to your lifestyle to ensure you’re forming habits that will last a lifetime.
At the Boden Group, Charles Perkins Center, we study the science of obesity and conduct clinical trials for weight loss. You can register here to express your interest.
Nick Fuller is Research Program Manager at the Charles Perkins Center at the University of Sydney. This piece first appeared on The conversation.