Can the secret to weight loss be found in a simple ratio?

The 5:2 diet sees followers fast twice a week, but does it really lead to weight loss and other health benefits?

You really can have your cake, eat it, and still lose weight – that’s according to fans of the so-called fasting diet, otherwise known as the 5:2 diet, in which you eat what you like for five days in the week, then consume next to nothing for the other two. Pounds will drop off you like magic, say proponents, who also claim that it could protect you from dementia, cancer and heart disease, and may even make you live longer.

British chef Hugh Fearnley-Whittingstall has just outed himself as a 5:2 convert. Keen to offset the effects of his Christmas gluttony, he has lost eight pounds since the New Year, and found the process left him feeling “lean and sharp” as well as curiously exhilarated. It all makes sense, according to Mr F-W: “Starve yourself once in a while, as our antecedents did for millions of years, by force of circumstance, and your body and digestive system go into recover and repair mode, giving rise to a whole host of physical benefits.”

Michael Mosley, the doctor and broadcaster who brought the 5:2 diet to widespread attention last summer, in a BBC Horizon documentary, is convinced that controlled fasting is the way to a longer and healthier life. Six weeks after starting the 5:2 diet, he underwent a full medical examination, and the results were impressive.

“I had lost well over a stone, down to less than 12st,” he wrote. “My blood glucose, which had been borderline diabetic, was normal and my cholesterol levels, previously high enough to necessitate medication, were also down in the healthy range.”

You can see why people like the idea of the fasting diet: instead of the soul-sapping ordeal of a regular calorie-controlled diet, where every day is mapped out in moments of denial, the 5:2 plan gives you five days of complete freedom where your appetite can roam wild.

Mouse-sized portions

Even those who chow down burgers and lasagne on the “feeding” days have reported weight loss. Okay, so you still have to revert to mouse-sized portions on the fasting days, which should be non-consecutive – restricting yourself to just 600 calories for men, 500 for women – but at least you have a large breakfast to look forward to on the following morning. The beauty is that the denial period never lasts for long.

Some people choose to use intermittent fasting not to shed excess weight but to boost their own performance. Running coach George Anderson, who runs public workshops across the Republic, fasts once or twice a week, for 16 or 24 hours at a time.

“I don’t use it for weight loss, I do it because it makes me feel good. It’s incredibly empowering. At first I was freaked out a little by the idea of not eating for so long. I felt a bit panicky, worried that I would get hungrier and hungrier as the day went on. But what you quickly start to realise is that the hunger comes in waves and it always passes. After a few hours you don’t feel hungry at all. Once you get over that psychological hurdle, fasting can be hugely beneficial. If you’re healthy, there are no downsides that I have come across.”

Intermittent fasting sounds almost too perfect: simple, effective, both mood and health boosting, and without the daily drudge of ordinary diets. But sending your body into starvation mode twice a week is a radical move, with potential risks and side effects. And the truth is that no one knows for sure what the long-term impact will be; there is simply not enough evidence, as yet, to justify the grand claims made for the intermittent fasting plan. Animal research shows certain possible health benefits, but there are important differences between a dieting rat and a dieting human being.

Dublin-based dietitian Paula Mee says that fasting for a day or two probably won’t do much harm to people who are generally healthy, provided they maintain an adequate fluid intake.

Yet Mee is concerned that the system is open to abuse, particularly among younger women who may be tempted to fast for longer, in the hope of heightened results.

“Fasting entirely for long periods of time can be harmful,” she says. “Your body needs a variety of vitamins, minerals and other nutrients from food to stay healthy. Not getting enough of these nutrients during fasting diets can lead to symptoms such as fatigue, dizziness, constipation, dehydration, gallstones, cold intolerance, not to mention vitamin and mineral deficiencies, which may result in osteoporosis or anaemia if continued over a prolonged period.”

Existing deficiencies

What’s more, if your everyday diet is poor, cutting back dramatically could exacerbate existing nutritional deficiencies.

The other question, according to Mee, is how long the weight will stay off? “When you fast, your body is forced to dip into energy stores to get the fuel it needs, so you will lose weight,” she says. “Our bodies have been genetically programmed to deal with the effects of fasting. When you eat less food, your metabolism slows down to conserve energy.

“When you go back to your usual diet, your lowered metabolism may cause you to store more energy, meaning that you will probably gain back the weight you lost and possibly even put on more weight when eating the same calories you did before the fasting diet.”

Psychological effects

And then there are the psychological effects. Rita , who home educates her two sons, tried the 5:2 diet last year, but found it impossible to sustain: “I got the fridge stocked with tasty low-calorie food to eat on my ‘fasting days’ – lean meat, salad, fruit – but what I wasn’t prepared for was the awful sense of emptiness. Not just in my stomach, although that was bad enough, it was gurgling away all day, and I felt quite cold and headachy with it too.

“Without the usual satisfaction of lunch or dinner to look forward to, the day passed very slowly, and I found myself counting down the hours to breakfast the next day. Then, when the next fasting day came round, I couldn’t face doing it all again.”

Some people find that the fasting diet leaves them feeling fragile and a little drained, unable to do much except languish on the sofa, sipping a cup of green tea. And that’s where the plan really falls down. “It’s out of kilter, the opposite of what we want,” says Mee. “We want people to exercise more so they can enjoy their calories, not to restrict their calories so much that they are unable to exercise.”

Mee says it’s better to be slightly overweight and fit, rather than skinny and unfit: welcome news to those who find that the fasting diet, with its extremes of denial and indulgence, leaves a bad taste in the mouth.