Eating one meal a day — or OMAD as it’s known in fasting circles — has become one of the more extreme trends in the intermittent fasting world. The appeal is understandable. It’s simple, it removes the daily mental load of deciding what to eat, and there are plenty of before-and-after posts online making it look like a shortcut to fast results. But is it actually effective, safe, and something most people can stick with? As a dietitian, here’s my honest take.
What Is the OMAD Diet?
OMAD is exactly what it sounds like: you eat one single meal within roughly a one-hour window and fast for the remaining 23 hours of the day. It sits at the extreme end of intermittent fasting strategies, well beyond the popular 16:8 approach (16 hours fasting, 8 hours eating) or the 5:2 method (two very low-calorie days per week). There is no specific guidance about what to eat during that one meal. The strategy is built entirely around timing and calorie reduction through restriction.
How OMAD May Support Weight Loss
The main way OMAD could lead to weight loss is a simple calorie reduction. When you compress eating into one meal, you may consume fewer calories overall because it isn’t realistic (or enjoyable) to eat a day’s worth of food in a single sitting.
But a theory is all we have to back up this claim. There is no published research that shows this approach actually leads to long-term weight loss or health benefits. The popularity has been seeded by social media influencers and anecdotal claims rather than research. In fact the only research I could find on this topic was a study that surveyed 24,000 adults after over 40 years and found that people who only ate one meal a day were 30% more likely to die from all causes and 80% more likely to die from heart disease compared to people who ate 3 meals a day.
Most studies available are more focused on intermittent fasting more broadly, and a 2022 study published in the New England Journal of Medicine found that time-restricted eating produced similar long-term weight loss to traditional calorie restriction. In other words, the results are comparable, not superior.
Potential Benefits of OMAD
So if isn’t better for weight loss, why would someone consider using this extreme fasting approach? For the right person, OMAD may offer a few advantages such as:
• Simplicity and fewer food decisions through the day, which can reduce decision fatigue and save time.
• Possible reduction in mindless grazing and late-night snacking habits. If having food rules doesn’t bother you, than the one meal rule provides a clear off switch on snacking.
• Short-term appetite awareness, as the fasting window can help some people reconnect with genuine hunger cues. This can also lead to an increase in mindful eating and appreciation of food.
Risks and Limitations to Consider
OMAD is not suitable for most people, and there are some meaningful risks worth understanding before you try it.
Muscle loss is a real concern. The body can only use around 20–25g of protein at a time for muscle maintenance and repair. Eating all your protein in one sitting means much of it gets used for energy rather than used for muscle repair and building. Over time, especially without resistance training, this can lead to a loss of lean muscle mass which slows your metabolism and makes maintaining weight loss harder in the long run.
Nutrient gaps are hard to avoid. Meeting your daily requirements for fibre, calcium, vitamins and minerals in a single meal is genuinely difficult. Chronic under-eating can lead to fatigue, poor immunity, and over time, effects on bone density and hormonal health.
Hunger is intense and persistent. After a 23-hour fast, ghrelin (your hunger hormone) spikes significantly, which makes it harder to eat slowly and mindfully. Many people find themselves eating rapidly and beyond fullness, which works against the appetite regulation benefits they were hoping for.
Sustainability is poor. Research on intermittent fasting shows dropout rates of up to 65%. OMAD is socially isolating and practically challenging as most family dinners, work lunches, and social occasions don’t fit neatly into a one-hour window.
It is not appropriate for everyone. OMAD is not suitable during pregnancy or breastfeeding, for people with a history of disordered eating, for those with diabetes or other conditions requiring regular food intake, or for active individuals with high energy needs.
OMAD vs Other Forms of Intermittent Fasting
When it comes to weight loss outcomes, OMAD does not outperform less extreme fasting approaches. The 16:8 method (eating within an 8-hour window and fasting for 16 hours) has considerably more research behind it and consistently shows comparable results and significantly better adherence and far fewer nutritional risks. You also have three or four eating opportunities throughout the day to spread your protein intake, which is much better for muscle maintenance.
The evidence does not support doing something more extreme to get better results. It just increases the risk of side effects and the chance you’ll give up.
Who Might OMAD Work Best For?
It is difficult to suggest who may benefit from this approach from a health point of view. I can see that there are working and lifestyle patterns where this would be helpful but I’d recommend treating OMAD as a short-term experiment rather than a permanent lifestyle, and checking in with your GP or a dietitian first.
Practical Alternatives to OMAD for Sustainable Weight Loss
If the appeal of OMAD is its simplicity and the removal of constant food decisions, there are gentler options to get that same benefit without the risks:
• Try a structured 12–16 hour eating window (for example, eating between 8am and 6pm), which aligns better with your body’s natural rhythms and has a significant base of evidence to support it.
• Put the focus on what you eat rather then when you eat. Build balanced meals around protein, vegetables, and high-fibre carbohydrates to keep you fuller for longer and reduce snacking.
• Use a meal replacement shake to simplify one or two meals per day while still meeting your nutritional needs. This can help reduce the decision fatigue and time spent preparing and stopping for meals.
• Consider if your food portions could be reduced to gently reduce your overall calorie intake. Start with reducing portions of your meals (except vegetables) and see how that feels and allow yourself some time to get used to each reduction.
• Reduce late-night eating by establishing a consistent kitchen close time in the evening. Cleaning up, turning off the lights and brushing your teeth can help seal the deal.
The Bottom Line
OMAD can produce weight loss for some people, but not because there is anything magical about eating once a day. It works because it reduces calorie intake and that same result can be achieved through far less extreme approaches that are easier to sustain and are better for you in the long-run.
The strongest predictor of successful weight loss isn’t the most restrictive strategy, it’s consistency. A moderate, flexible approach you can stick with will always outperform an extreme plan that lasts three weeks before your body (and social life) demands otherwise.
