healthHealth and Medicine

What Is The OMAD Diet And Does It Work?

Just another fad or does this one have promise? The answer is, well, you can guess.

Russell is a Science Writer with IFLScience and has a PhD in the History of Science, Medicine and Technology

Dr. Russell Moul

Russell is a Science Writer with IFLScience and has a PhD in the History of Science, Medicine and Technology.

Science Writer

A table of healthy food including salmon, vegetable and grains.

The OMAD diet has gained some popularity, but how does it compare to other intermittent fasting diets?

Image credit: Antonina Vlasova/

It seems there’s a new diet on the scene (another one), which is being touted by various supporters such as Bruce Springsteen, Coldplay’s Chris Martin, and the British Prime Minister, Rishi Sunak. But what is this new fad and how does it work?

Just another intermittent fasting diet?

OMAD stands for One Meal A Day, and is basically what it says on the tin. It is a type of time-restricted diet that relies on intermittent fasting, which can – so its advocates claim – promote fast weight loss, possibly improve health, and even slow aging. Notice the use of conditional language here. As with all new diets, one must take the claims made by supporters with a pinch of salt (unless you’re on a salt-free diet).


There are plenty of intermittent fasting diets out there, each recommending different periods of time (usually between 12 and 24 hours) to go between meals. Generally speaking, these diets advise you to avoid consuming, either through solid food or through beverages, any calories. You are therefore allowed to consume fluids such as coffee or water (or anything else that is calorie free).

Among the more popular intermittent fasting diets are the time-restricted diet, which involves fasting for at least 12 hours every day and only eating during the final hours of this period. This is often referred to as the 16:8 method, in which you fast for 16 hours and then fit in meals within the remaining eight hours.

Another method called the 5:2 diet involves eating “normally” throughout the week, but then fasting and restricting your calorie intake to about 500-600 calories over the remaining two days.

There are plenty of others too, which vary on how many days one should fast and for how long. So what makes OMAD special? Well, not a lot, it’s just a bit stricter.

One meal to rule them all

Essentially, the OMAD diet requires you to fast for 23 hours and then to consume your daily calorie intake in a single meal within that last hour. There are no restrictions on what you consume to achieve this calorie count, only that you do so in the prescribed time. Throughout the day, you’re allowed to drink calorie-free substances like water, black tea, and coffee.

The only other prescription is that you should eat your calorific meal during the same hour each day – consistency is, apparently, key.

As with all the other intermittent fasting diets, the plan is to put the body into a state of ketosis, where it burns stored fat for energy, rather than relying on glucose.

Does it work?

Prepare for an equivocal shrug. At present, the evidence for the effectiveness of this diet is limited. The existing studies have mostly focused on animal subjects and the main study that used humans involved 11 lean, young people who followed the diet for 11 days.


According to a recent Conversation article written by University of Sydney researcher Nick Fuller, the OMAD diet typically relies on research from other intermittent fasting diets, rather than relying on its own method. Although there is some evidence that intermittent fasting can help with weight loss, the studies tend to focus on short periods of time, rather than prolonged periods. The evidence for longer term reliance on fasting does not seem promising.

Fuller continues to explain the potential hazards that come with the OMAD diet. They mostly revolve around the lack of guidance for how to balance all the needed nutrients within a single meal. The food we eat every day needs to include protein, wholegrain carbs, vegetables, fruits, and “good fats” to operate properly and prevent illness. Being able to find a single super meal that captures this complexity is extremely unlikely and so the OMAD diet risks making people unwell.

It is also likely that such a severe fast will leave people feeling uncomfortably hungry for long periods of time, raising the risk of eating the “wrong” types of food when your allotted hour comes around.

Finally, the whole practice is probably extremely unsustainable. It is not fun, it is not enjoyable, and so it is not likely to survive. As with any quick-fix efforts to lose weight, the promises of these diets are fluff and fantasy. In fact, as Fuller points out, once your body starts to lose weight, it will likely switch into a conservation stage where it actually fights to retain fat – this is part of our hunter-gatherer heritage, where the body anticipates a period of deprivation and so tries to store more fat for the hard times.


As boring as it is, Fuller suggests the best way to lose weight is to ensure a healthy lifestyle of regular exercise, sufficient sleep, and a well-balanced diet. Such changes to lifestyle and diet should be implemented in gradual stages so that they remain sustainable.

The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.  

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current. 


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