The one meal a day diet: Devotees tell how they’ve lost vast amounts of weight and even seen bad skin clear up. But there’s a dark side…

For Catherine Corless, a ­typical weekday supper is roast pork, piles of ­crackling, broccoli and celeriac mash, then Greek yoghurt with berries, a handful of nuts and a few squares of dark chocolate. Her plate full, her appetite sated.

So you might wonder how Catherine, 62, a teacher from Cardiff, managed to lose an astonishing 6st 7lb in a year. In 12 months, she dropped from a size 22 to a slim 12-14.

But there is a – highly controversial – catch. Although Catherine might fill her plate at dinner, that meal is all she eats each day. No breakfast, lunch or snacks at all.

Catherine Corless has lost 6st 7lb in a year thanks to the OMAD diet

Welcome to the One Meal A Day diet, or OMAD, one of the most extreme intermittent-fasting regimes. Devotees say it can not only help you lose weight, but change a ­lifelong unhealthy relationship with food. Experts are quick to highlight potential health issues, but Catherine is a convert.

‘I’ll never return to three meals a day,’ she says. ‘It’s not just that I can bend to paint my toenails now. I’m more ­confident, too.

‘My memory has improved and I’ve stopped equating food with emotion. You find yourself completely changing who you are as a human being. This is a really healthy way to eat.’

These are bold claims but Catherine isn’t alone in believing them. The OMAD eating plan has soared in popularity. An ­Instagram search for #omad yields many thousands of pictures of enormous dinners and ­slimmer figures.

Broadcaster Carol Vorderman has revealed she follows the plan, admitting she has one meal ‘late in the afternoon’ and snacks on raw sprouts when hunger pangs strike.

Coldplay singer Chris Martin took up the diet after realising rocker pal Bruce  Springsteen – a devotee and 28 years his senior – was ‘in better shape’ than him.

Jack Dorsey, the billionaire co-founder of Twitter/X, has claimed eating ‘seven meals every week, just dinner’ gives him a ‘new dimension’. He claims ‘the day feels so much longer when not broken up’ by meals.

Some say OMAD promises a more youthful appearance and better mental health.

Others are attracted by its sheer ­simplicity. TV medic Dr Xand van Tulleken has followed the diet sporadically. He believes OMAD can be ‘surprisingly convenient for many dieters, as it produces weight-loss results without the hassle of excessive meal preparation, juicing or calorie counting’.

Why obsess over what to eat or avoid, when you can simply take food out of the equation for all but an hour a day?

And yet OMAD is not without its critics. Nutritionist Nicola Shubrook says OMAD may contribute to disordered eating, fuel hormone imbalances and disrupt sleep.

In particular, she says, it’s hard to eat enough protein in one meal to sustain and build muscle.

A woman weighing 60kg (9st 6lb) needs a minimum of 80-100g ­protein a day, the equivalent of two steaks or chicken breasts in each of those once-a-day meals. And if this one meal is filled with refined carbohydrates ‘it may affect blood sugar levels, leading to lethargy, mood swings and cravings’.

Shubrook adds that low blood sugar levels or ­dehydration may cause headaches or migraines.

‘The body could produce more of the stress hormone cortisol in an attempt to raise blood sugar levels, which may have a knock-on effect of decreasing progesterone levels, leading to low mood and anxiety,’ she says. She also stresses that nutrient deficiencies could lead to anything from anaemia and fatigue to constipation.

Broadcaster Carol Vorderman is a devotee of OMAD

‘There will always be people who say OMAD suits them, but for the majority of us leading busy lives, I don’t think it’s a healthy approach.’

Catherine Corless insists, though, that OMAD was the key to reversing weight gain from comfort eating as a new mother, undiagnosed hypothyroidism and perimenopausal hormone changes.

Throughout her 40s, her weight ballooned from 13st to 18st. She tried Weight Watchers, the Atkins diet and meal replacement shakes – but then found The Obesity Code book by Dr Jason Fung, a diabetes specialist who believes fasting can regulate hormone levels to control weight.

Other benefits to eating one meal a day, says Dr Fung, include being able to work through lunch and ‘a ­dramatic reduction in your weekly grocery bills’.

‘It made a lot of sense,’ says Catherine. ‘I have a big appetite but can go for long periods without eating and was irritated by diets where you had to divide calories into small meals that don’t satisfy you.’

She decided to follow a low-­carbohydrate version of OMAD, eating at 6pm so she could share dinner with her son James, who’s now 18, and substituting the chips and pasta he ate for vegetables.

Today, Catherine ensures she eats plenty of meat or cheese for ­protein – above the daily requirement – and estimates her daily ­calorie intake is around 1,600.

There is no set limit to the ­number of calories you should ­consume with OMAD.

She admits the first days of her 23-hour-a-day fast were tough, but says the pressure soon eased when her body adapted to burn fat rather than carbohydrate for fuel. The process, known as ketosis, is key to OMAD’s efficacy, ­converts say.

Catherine says she’s suffered few side-effects – but does admit to having three, 90-second episodes of ‘kaleidoscope vision’, or visual migraine, on day ten of the regime.

Nicola Shubrook says this may be due to stress or hormone imbalances, which can be exacerbated by nutrient deficiencies.

‘The physical feeling of hunger only lasts a few days,’ insists ­Catherine. ‘After that, it’s very much a mind game. In the ­losing phase, you’ve got to have a strong enough reason to refuse cake.’

She lost 6lb in her first week. By last July, she’d lost 6st 7lb and weighed 11st 6lb – a weight she maintains today. She hasn’t considered ditching the diet.

She says her social life hasn’t suffered. When invited to restaurants with friends, she moves her meal to later in the evening, and eats a few nuts at 4pm to keep going. ‘I’ll have a coffee with unsweetened almond or coconut milk if I’m invited to a friend’s house for brunch – I’m there for the company, not the food, and they understand. I don’t feel I’m missing out.’

 Lara ­McLarnon gave up on OMAD after putting on 7lb in the first three weeks

Nor does she wake up ravenous: ‘Your body resets overnight. Not eating in the day is soon a habit.’

She drinks wine occasionally. ‘I was a regular drinker, but don’t miss it,’ she says.

Even her memory has improved. ‘I can memorise strings of numbers I need to type out for work. I used to have to go backwards and ­forwards between computer screens.’ She also credits the diet with other physical changes.

‘I’d had a few skin tags, like raised brown freckles, on my neck for years. Within three months they’d dropped off,’ says Catherine. Skin tags can be associated with insulin spikes. Anecdotally, fasting has been linked to a lower risk of them developing.

There is even some ­evidence to back up her claim of improved memory. When the body uses fat stores for energy, fatty acids called ketones are released into the bloodstream in a process shown to protect memory.

Last year, a study on mice carried out at the University of Southern California found fasting could even lower the risk of Alzheimer’s. Clinical trials have also linked it to longer life and a lower risk of heart failure.

Others advise caution, however – especially for women.

The Oxford Longevity Project, which brings together scientists from around the world to discuss ageing, found OMAD’s extreme fasting works better as an anti-ageing strategy in men.

Project co-founder Leslie Kenny says: ‘Women are built for reproduction – so when we eat one meal a day, the body can shut down fertility since it perceives resources as being too scarce to bring a baby into the world.

‘OMAD has lots of benefits, but it is not a one-size-fits-all answer, especially for women.’

Some who’ve tried it have a very different experience to ­Catherine’s. Lara ­McLarnon gave up on OMAD after putting on 7lb in the first three weeks. ‘It was too extreme for me – my body went into starvation mode,’ says Lara, a charity worker from West Dunbartonshire.

Donia Youssef says she feels energised after losing a stone on the diet

Newly single on starting the diet, she had put on more than 2st during a two-year relationship and, at 5ft 7in, weighed 14st.

‘I’d been comfortable in my relationship and ate too many treats,’ she says. ‘I was ­horrified when I weighed myself and discovered I was technically obese.’

She came across OMAD on ­YouTube, thinking it would be as good for her purse as her ­waistline. She ate her single meal at 11am, consuming a variety of ‘substantial’ dishes, from slow-cooked casseroles to rice and sushi.

‘By 7pm I’d feel ravenous and irritable. I’d try to hang on, but would cave by 9pm and ­sometimes eat a crisp sandwich.’

After a fortnight, she’d gained 5lb and despite persevering – ­feeling ‘sluggish and lethargic’ and suffering headaches – for another week, put on two more pounds.

She gave up and went on to lose 9lb with the common sense method of exercise and restraint: three months of regular swimming and cutting back on snacks.

Lara says: ‘I was trying to do something good for myself. But everyone’s body is different and, for me, OMAD didn’t work.’

On the other hand, Donia Youssef, 46, an author and ­filmmaker from Grays, Essex, says following OMAD for nine months has been life-changing.

‘It’s lifted a heaviness. I feel energised. I’ve changed the way I think about food,’ says Donia, who has lost a stone on the diet and now, at 5ft 1in, weighs 9st 1lb and is a dress size 8-10.

Her weight had soared to 13st after going through early menopause aged 40 when doctors removed her ovaries following a breast cancer diagnosis.

‘I was bloated and tired all the time,’ says Donia, who heard about OMAD from a friend. ‘My friend swore by it, and I liked the fact I wouldn’t have to worry about what I ate.’

Donia, a single mother, pictured before she started the OMAD diet. One of her friends said it’s not healthy

A single mother, she had her meal between 4pm and 5pm, when her children returned from school, so she could enjoy the same rice and pasta dishes or roast dinners she made for them.

She lost 7lb in the first fortnight – ‘it was quite drastic, I was ­surprised’ – yet admits that for those first two weeks she was ‘irritable as hell’ and ‘starving’.

‘I felt bouts of dizziness at about 4pm. It took a couple of months for the hunger pangs to go. I’d fill up with fluids to stop them.’

But then, she believes, her stomach shrank – and the cravings stopped. ‘I don’t feel hungry any more. I can’t even finish my meal most nights, as I’m full,’ says Donia. If she fancies pudding, she will enjoy apple pie and custard, or cake, and estimates she ­consumes 1,500 calories a time.

‘My skin is clearer – I used to get spots, but don’t any more – my hair grows quicker, the bloating has gone and I’ve stopped needing to take vitamin ­supplements.’ She hasn’t told her doctor she is on OMAD, though: ‘They’d probably say you need to eat three healthy meals a day. But my BMI was higher when doing that.’

While fasting is not advised for those having cancer treatment, due to the risk of not getting enough nutrients, studies on ­animals show it can lower the risk of cancer, as it may reduce ­glucose levels in the blood.

Donia believes she is a better mother due to her new diet. ‘We’re spending quality time ­eating dinner together earlier, when the kids are not as tired. I’m sharper in the morning, ­getting the kids to school. And I’ve saved around £100 a week.’

She is only tempted to break the diet when the children are eating biscuits: ‘I chew gum.’

Donia admits she’s encountered dissenters: ‘When friends ask how I keep my figure, I say I only eat one meal a day. One said I’m nuts and it’s not healthy.’

Regardless of Donia’s success on the diet, many would agree.