OMAD diet: What is it?

Find out more about the OMAD diet and why it’s not recommended by our nutritionist.

5:2, 16:8, alternate day fasting, OMAD – we’re seeing more and more diets based on time-restricted eating schedules. All of these intermittent fasting regimes take the focus away from what food you eat and instead concentrate on restricting when you can eat it. The pattern of when you fast and when you feast varies between specific diets, but OMAD is the most extreme. So, what’s the theory and can it work?

What is the OMAD diet?

OMAD stands for one meal a day and is an extreme form of intermittent fasting.  With the OMAD diet, there’s a single one-hour eating window every day. You fast for the other 23 hours. The theory is you can eat what you like as long as it’s consumed during the same one-hour slot every day.  Eating in this way creates a calorie deficit, which can lead to weight loss. The OMAD rules summarised

  • 23 hours of fasting, one hour for eating. There’s one hour per day for eating and the remaining 23 hours are calorie-free.

  • A consistent eating schedule. Eat your one meal in the same one-hour time block every day.

  • Drink whenever (as long as it’s calorie-free.) Drink only calorie-free beverages such as unsweetened tea and black coffee, or water during the 23-hour fast.

  • What you eat is up to you. OMAD doesn’t set a calorie limit or restrict the types of food you eat during your single meal.

OMAD benefits

There are some health benefits associated with longer periods of fasting. For example, improving insulin sensitivity. But it’s unclear whether these advantages extend to the OMAD diet.

But what about OMAD weight loss? If you eat just one meal a day, you’ll probably lose weight because, chances are, you’re taking in less calories than you would eating three meals per day. But there isn’t convincing evidence to suggest the OMAD diet will lead to any more overall weight loss than a conventional calorie cutting regime.

But still, it has many supporters. The main appeal of the OMAD diet is losing weight while eating whatever you please. If you hate calorie counting, this diet doesn’t require you to read labels obsessively. It also doesn’t ask you to consider the nutrient balance of your meals. In short, the upside to this diet for many is the simplicity – the minimal need for meal planning and complete absence of calorie tracking.

And what about the downsides of the OMAD diet?

Hunger is a powerful sensation – quashing it for 23 hours straight takes willpower. Most people will find eating one meal per day difficult to stick to. But is OMAD bad for you? Possibly. The diet isn’t suitable for everyone.

Skipping meals can be particularly unhealthy for people with certain conditions. For example, diabetes, anyone taking medication for heart disease or blood pressure regulation, and if you have an eating disorder. Children, pregnant or breastfeeding women, and older adults should also avoid this extreme form of time-restricted eating.

But for anyone, eating in this way can end up doing more harm than good. This is largely down to it being very difficult to get a full variety of nutrients in OMAD diet meals. Therefore, an unwanted side effect could be nutrient deficiencies. Enduring long hours without eating can also lead to bad eating tendencies. For example, you may find you have increased urge to binge-eat on unhealthy options during the one-hour eating window.

What our nutritionist says

Is OMAD healthy? We asked Emily Rollason, Holland & Barrett nutritionist, to share her thoughts on the OMAD diet:

"Whilst there are studies showing some benefits of fasting, I feel there’s more research to be done to fully understand the full impact of this diet. OMAD does seem extreme. I imagine starving yourself in this way could make you extremely tired, hungry and irritable for most of the day."

"It’s also difficult to consume all the calories you need in a day in a one hour meal sitting. But there are other factors to consider as well as the impact of not eating sufficient calories. Firstly, the quality of the meal. It’s unlikely that you’ll get all the nourishment you need in one meal, so there’s potential to become deficient in certain nutrients. Another big factor for me is whether such tightly restricted eating could feed into a disordered eating pattern."

"Overall, I wouldn’t recommend this diet. If you want to try intermittent fasting, there are other less extreme versions that are more balanced and with less restricted fasting windows. But my advice is always to seek the guidance of a professional dietician or nutritionist before following any time-restricted eating plans."

Summary: Should I try the OMAD diet?

There’s clearly an appeal of a diet which allows you to lose weight while eating whatever you like. But the reality is that for most people the OMAD diet isn’t sustainable. Overall, following a nutritionally balanced, lower-calorie diet is a healthy and more maintainable route to weight loss.

Last updated: 18 August 2020