Examining the 5/2 Alternate Day Fasting Diet

By | February 12, 2013

Gorging yourself on as many burgers, chips and cakes as you like one day then eating fewer calories than you find in a cheese sandwich the next might sound like a worrying eating disorder.

But this regime of chomping away to your heart’s content one day, and virtually starving yourself the next is the latest diet craze. It’s known as ‘intermittent fasting’ or ‘alternate-day dieting’,and devotees insist the pounds just drop off.

The diet soared in popularity after featuring in a BBC2 Horizon documentary a few weeks ago by health journalist Dr Michael Mosley. After a month eating normally five days a week and eating just 600 calories the other two days — known as the 5/2 diet — Mosley lost nearly a stone, reduced his body fat by about 25 per cent and improved his blood sugar and cholesterol levels.

Scientific data seems to show that as well as helping to shift pounds, this alternate-day dieting can help us live longer and reduce the risk of diseases such as cancer, diabetes and even Alzheimer’s.

Now a book on the subject, The Alternate Day Diet, is on Amazon’s list of best-selling diet books, while on internet forums, fans of the plan are swapping tips for the best low-calorie meals for fast days.

However, the regime has drawn criticism from nutritionists who believe that any weight loss on the diet would not be sustainable — and claim that it could even trigger eating disorders.

‘The idea that you have a very restricted diet on your “fast” days and can eat whatever you like on your “feed” days isn’t something I’m very comfortable with,’ says Zoe Harcombe, author of The Obesity Epidemic book.

‘I did this during my late teens and early 20s. It was called bulimia. My biggest concern is that it’s an approach that could encourage disordered eating in people who are prone to that sort of behaviour.’

While every dieter will be used to hunger pangs, the side-effects of such extreme calorie restriction can be even more unpleasant.

‘The body does its best to get us to eat,’ says Zoe.  ‘So if you’re only eating a quarter of the calories you need, you can expect to experience symptoms associated with low blood sugar. Anything from feeling light-headed and having shaky hands to feeling irritable and lacking concentration.’

The diet can also cause digestive problems. Followers are encouraged to up their water consumption on low calorie days.

If they don’t, they can find themselves constipated, with all the associated stomach cramps and bloating. Despite such concerns, many swear by the plan.

Adriana Wheatley, 27, from Solihull in the West Midlands, first tried alternate-day fasting three years ago after reading about it in a magazine. ‘I’d put on quite a lot of weight at the time,’ she says.

‘I’m 5ft 9in tall and normally wear a size 10 to 12, but I’d gone up to 11 stone, my clothes were tight and I was a big size 12, which I’d never been before.

‘I decided to try a day of eating normally alternating with a day of eating just 500 calories a day.

Understandably, her family and friends were concerned.

‘Even after I’d explained all the benefits, they still thought it sounded ridiculously extreme,’ she says.

However, Adriana, who is head of customer relationship management for a retail firm, was undeterred, and stuck with it.

‘I did it for only a couple of weeks but the results were amazing. I lost seven pounds, and I pretty much kept it off until earlier this year, when a lot of holidays and letting my gym routine lapse meant it started to creep back on again.’

Adriana saw the Horizon documentary and was inspired to give another go to a less regimented version of the fasting diet.

‘This time around, having seen the programme, my friends were more encouraging, and my best friend has even started doing the diet herself.’

But like any tough diet regime, it has affected her social life.

‘When I did it the first time, I was doing strictly alternate days.

‘That did make it hard and, in fact, I had to go to a wedding on a fasting day, which meant it was impossible to stick to the 500-calorie limit.

‘But this time, I’m fasting for only three days a week, which makes things much more flexible.

‘I fast on Monday, Wednesday and Friday, leaving the weekend free for me to eat what I want.’

On her fast days, Adriana chooses to skip breakfast and has a 270-calorie supermarket salad for lunch — and uses the rest of her calorie allowance on fruit including bananas and apples.

Two weeks in and eight pounds down, she seems to have avoided unpleasant side-effects. But she admits there are downsides.

‘I avoid exercising on my fast days as I worry it would make me feel faint, but most of the time it’s fine. I do go to bed a bit grumpy and hungry, but the thought of eating whatever I want the next day keeps me going.’


Anything you like

Breakfast: 2 eggs scrambled and a slice of ham (250 cals)
Lunch: Nothing
Dinner: 100g (uncooked weight) skinless chicken breast, grilled, served with 150g new potatoes, boiled, and 100g broccoli, steamed (259 cals)

Anything you like

Breakfast: Kedgeree made from 100g cooked smoked haddock, 50g (uncooked weight) of wholegrain brown rice, boiled, and a spring onion (265 cals)
Lunch: Nothing
Dinner: 100g fillet steak, grilled, served with 100g wild rocket and 100g carrots, boiled (242 cals)

Anything you like

Anything you like

Anything you like

While the idea that you can eat anything on your free days sounds great — especially for dieters who struggle to stick to low-calorie eating plans long-term without falling off the wagon — many nutritionists believe that those on the alternate day diet could end up over-indulging on ‘feast’ days, and actually put on weight.

However Dr Krista Varady of the University of Illinois in Chicago, one of the scientists involved in research into intermittent fasting, insists that this doesn’t happen.

‘Our studies show that people end up losing weight because they can’t fully make up for the lack of food on the fast day on the feed day. And people in our studies didn’t binge. They only ate about 100 per cent to 110 per cent of their calorie needs.’

Her findings fit in with what Adriana Wheatley discovered.

‘I think because, unlike other diets where certain foods are restricted, you know that you can have whatever you want, you’re just a bit more relaxed about things. I don’t go crazy on my feed days, but I might opt for a sandwich rather than having a salad, and have pasta, which in the past I might have avoided if I was trying to lose weight, but I don’t go over the top,’ she says.

Opinion is divided on just exactly what a fast entails — some say you should eat nothing at all for anything from 17 to 24 hours, while others argue that you can have 500 calories, but they should all be consumed in a single midday meal.

Michael Mosley on the Horizon programme ate his 500 calories split over two meals, breakfast (ham and eggs) and dinner (steamed fish and vegetables), as he found that was the best way to avoid feeling hungry or deprived.

Nutritionists do agree that it is vital to eat nutrient-rich foods if you only eat 500 calories a day.

A brunch of kedgeree made from 100g of smoked haddock, 50g of wholegrain brown rice and a spring onion, and then a dinner of 100g of grilled fillet steak with 100g of steamed broccoli would give you a balanced diet and fall within the calorie restrictions.