What eating one meal a day does to your body – and what results can you see after a month?

NZ Herald

23-04-2025

'In individuals with no underlying health concerns, consuming fewer calories than you expend leads to weight loss, and people who eat once a day typically will eat far less than they need to maintain their weight,' nutritionist Jenna Hope says.
But there is more to the one meal a day, or Omad, diet than this. Fasting, or leaving time between meals, 'has a number of other health benefits, including reduced inflammation, improved digestion and focus and improved digestion,' says April Morgan, head of nutrition for the supplement brand Artah.
Could cutting your food intake to one meal a day really make you slimmer, healthier and more productive? We asked the experts.
What is the Omad diet?
At its most basic, the Omad diet is exactly what it sounds like: a diet plan that involves eating just one meal a day. But when it comes to how eating this way can change your body, there's a bit more to it than that.
'The Omad diet involves a one-hour eating window a day, meaning that you're fasting for 23 hours in total,' says Morgan. This makes the Omad diet similar to intermittent fasting, where people restrict their eating to a window of eight to 12 hours and fast for the rest of the day and overnight. 'The effects of fasting on each person who does it are very individual,' Morgan adds.
For this reason, most people who follow the diet won't break their fasts with any form of calorie intake, including sweetened drinks or milk in tea and coffee. Black tea, herbal tea and black coffee are all allowed within the diet as they don't contain calories, so long as they aren't sweetened. Water is allowed too, and drinking enough of it — two and a half litres or about four pints — is 'definitely important' to keep yourself going, says Hope.
OMAD diet plan
If you're going to eat one meal a day, you might expect to make it breakfast. 'I'm all about following our natural body clocks, which means eating more in the early part of the day than we do in the evening, as this aligns with all our bodily processes and gives us more energy, better digestion and sleep,' says Morgan. 'But if you were to eat your only meal as soon as you wake up, you would likely be very hungry by bedtime, and going to bed without having eaten can disrupt your sleep as your blood sugar drops in the night.'
Instead, it would be wise to start the day with hydration in the form of water and herbal teas, potentially with added electrolytes, advises Morgan, to help stave off hunger until later in the day. 'Most people find it much more manageable to fast in the daytime and then eat when they're home from work,' she says. The crucial thing is to eat your one meal at the same time each day, 'so that you achieve the full 23-hour fasting window'.
Your one meal, whenever you eat it and whatever it consists of, 'should contain at least 1200 to 1400 calories,' says Hope, 'as this is the minimum you need to consume a good range of micronutrients and fuel your body properly while enabling a safe rate of weight loss'. It's also important not to eat the same meal each day, Morgan adds, 'to get a proper variety of nutrients given your low food intake'.
It is possible to exercise on the Omad diet, 'but I absolutely wouldn't recommend any strenuous exercise like strength training, as you will put strain on your muscles and not be able to recover properly afterwards, meaning you'll do more damage than good,' says Morgan. Gentle exercise such as walking, swimming, yoga and Pilates are all safe to carry out.
While Morgan recommends eating your meal after any exercise, 'to refuel and nourish,' Hope believes it would be better eaten before any exercise 'to give you the energy you need'. In either case, exercising will be tricky, 'as you'll expend more energy, meaning that you really need more food than you otherwise would have,' Hope says. 'This is one reason why I don't recommend this diet — it can inhibit the other factors that make up a healthy lifestyle'.
What kind of results can you see after one month on the diet – and after three months?
'The amount of weight you lose on this diet depends on the weight you're starting at, and how much you're eating in each of your meals,' says Hope. Though there is some evidence to support fasting as a more impactful weight loss method, 'you're unlikely to lose any weight if you eat a meal that contains the amount of calories that you need to eat each day to maintain your weight'.
Losing a kilogram requires a deficit of 7700 calories. To lose this much weight in a week would mean eating 1100 fewer calories than you need each day. The average British woman — at 73kg and 162cm — could therefore expect to lose half a kilogram each week by eating one meal a day, containing no less than 1200 calories. The average British man, meanwhile, weighing 85kg and 175cm, might expect to lose about a kilogram.
Over a month, this means the average woman could lose 2kg, while the average man might lose 4kg. After three months, each might have lost 6kg and 12kg, respectively.
Advertise with NZME.
A smaller meal would result in more rapid weight loss, but with the safe rate of weight loss being 0.5-1kg a week, according to Britain's NHS. 'It's important not to cut your calories dramatically,' says Hope.
While fasting can prompt your body to burn fat, eating in such a restricted way can also lead to lean muscle mass loss. This might not affect someone who is overweight to begin with, but someone who eats one meal a day at a healthy weight could notice the loss of muscle mass. Research into the likelihood of this while doing the Omad diet is lacking, but one study has found several months of intermittent fasting can cause people to lose 1kg to 2kg of muscle.
It might not sound like much, but this kind of change in your body composition can lead to a less toned look, even after losing fat. Eating an extremely small meal once a day would likely lead to more muscle loss than this.
What are the benefits of the Omad diet?
Some of the benefits of the Omad diet include:
Increased fat loss
Better focus
Increased energy
More time
Improved gut health
'When you fast for between 12 and 17 hours, the body starts burning fat as fuel rather than sugar. After the 17-hour mark, your body goes into autophagy, a process in which old cells get 'cleaned out' of the body and new cells are produced,' says Morgan. This can make Omad more powerful than intermittent fasting, which has longer eating windows of six to eight hours and typically involves skipping breakfast and eating your last meal of the day before 8pm.
Then there are the impacts of fasting on our brains. 'Lots of people report that they can think more clearly and more efficiently while fasting,' Morgan says, an experience also well-represented in scientific studies. Some research indicates that fasting improves cognitive function, boosts neuroplasticity (the brain's ability to adapt) and even protects the brain against injury and disease.
Advertise with NZME.
'Fasting can also improve your gut health, as it gives your gut time to rest and repair. When your gut lining is compromised, this can lead to bloating, gas, burping and irregular bowel movements,' Morgan adds. 'I often recommend eating one meal a day a few times a month to clients who have gastrointestinal problems, as it can help to relieve pain and bloating and promote healing.'
Some people benefit more from the Omad diet than others. 'Middle-aged men might find this diet helpful, as they can often struggle the most to lose weight,' says Hope.
Some people who are put on highly restricted diets by their doctors might prefer to eat only once a day. 'Patients who are prediabetic or in the early stages of diabetes might eat once a day, because doing so reduces the frequency of insulin spikes, making their blood glucose levels easier to keep under control, although these individuals should always seek personalised professional advice when changing their diet,' explains Hope.
What are the risks?
These are some of the risks associated with the Omad diet:
Nutrient deficiency
Loss of lean muscle mass
Fatigue
Disordered eating
Change in metabolism
'If you're eating just once a day, it's very difficult to consume all the nutrients you need,' says Hope. 'This can lead to nutrient deficiencies and symptoms like muscle weakness, irritability, brittle nails and hair and fatigue.'
While fasting can promote rapid fat loss, it can also lead to the loss of lean muscle mass if carried out too frequently. This can have detrimental effects on your health, as 'your muscle mass is really the metabolic organ for your whole body, and dictates a lot of your hormonal activity,' Morgan explains. Muscle mass naturally decreases with age, making this particularly troublesome for older people. A lack of muscle mass causes frailty, falls and increased risk of an earlier death.
Advertise with NZME.
'Fasting for long periods can also be very disruptive to women's endocrine systems, which can increase stress and actually lead to weight gain in the long term,' says Hope. 'For this reason, I'd be especially cautious about recommending the Omad diet to perimenopausal or menopausal women.'
What's more, 'your body will adapt to the plan over time and start to conserve more energy, meaning that you likely won't lose as much weight and you might find it hard to lose weight in the future, as your metabolism won't work in the same way,' Hope says.
One study, involving 32 people split into two groups, found that the metabolisms of those who ate 1114 calories a day slowed over twice as much as those in the other group, who ate 1462 calories each day — yet both experienced similar weight loss. Such an effect 'is one reason why I suggest that people 'cycle' on the Omad diet, following it for only a few days a month,' says Morgan.
What should you eat if you only have one meal a day?
'If you're going to eat one meal a day, at least a quarter of your plate should be made up of lean protein like chicken, salmon or tofu,' says Hope. 'Another quarter should be complex carbohydrates such as quinoa, sweet potatoes or brown rice. A quarter should be non-starchy vegetables like broccoli or cauliflower, and the last quarter should be a healthy fat, like nut butter, avocado, hummus or cream cheese. Focusing on whole foods is crucial, as this will give you the highest possible amount of nutrients.'
FAQs
What are the rules of the Omad diet?
'The only rules are to eat once a day and avoid breaking your fast,' says Morgan, 'but, personally, I'd add to this that you should also drink plenty of water, consciously curate your only meal around protein, fat, and fibre, with four handfuls of different coloured vegetables, and some complex carbohydrates.'
Can you do an Omad carnivore diet?
Yes, says Morgan. 'The protein involved in an all-meat Omad should keep you full, but as a nutritionist, I would prefer to see someone having some leafy vegetables along with that, too.'