The 5:2 diet works — but the side effects are pain, misery and bad breath

    2 February 2016

    The body is a temple. In January, for the most part, it is a rather large and overfed temple. This year, under the pressure of constant lifestyle and dietary advice, I decided on a remedy: the intermittent fasting diet.

    The regime, which instructs dieters to feast for five days a week and fast for the remaining two, originally took the States by storm in 2013. It has gradually crept over the pond, with numerous bestselling books (The Fast Diet: Lose Weight, Stay Healthy, Live Longer and The Fast Diet Recipe Book) and celebrity adherents (Benedict Cumberbatch). In fact, it’s not just contemporary ‘celebs’ who are singing its praises: Plato once said ‘I fast for greater physical and mental efficiency’; Aristotle was said to be a faster, too. Martin Luther announced: ‘It is right to fast frequently in order to subdue and control the body.’

    So what is it? The diet — more commonly known as the 5:2 diet — dictates that you only need acknowledge it twice a week. On these ‘fasting days’, dieters are advised to consume 25 per cent of the recommended daily calorie intake (that’s 500 calories a day for women, and 600 for men). The 5:2 was originally championed by TV medic Dr Michael Mosley and journalist Mimi Spencer.

    There are, famously, two golden rules of dieting: never crash diet and never skip meals. Yet the 5:2 seemingly encourages the former, and, it would seem, does not reject the latter. A website claims that ‘it’s easy to comply with a regime that only asks you to restrict your calorie intake occasionally. It recalibrates the diet equation, and stacks the odds in your favour’. So far, so easy.

    Five hundred calories a day seems shockingly restrictive, yet Mosley and Spencer’s book suggests it is easily possible to divide such a meagre allowance into three meals. Combinations include a breakfast of two Ryvitas spread with two teaspoons of Marmite, a ready-made vegetable soup for lunch, and a supper of a small steak or fish fillet with mixed leaves. Dieters are encouraged to split their ‘fast days’; black coffee, Diet Coke, green tea and water (go crazy) are all allowed.

    Little is known about the long-term effects of intermittent fasting (IF). The NHS guidelines state that ‘despite its increasing popularity, there is a great deal of uncertainty about IF with significant gaps in the evidence,’ and that possible side effects include difficulty sleeping (it’s true — I woke up regularly with severe hunger pains), bad breath (quite likely), irritability (the most prominent), anxiety, dehydration (thank goodness for the water allowance) and daytime sleepiness.

    So far, so unappealing. Yet there is evidence to support intermittent fasting — we don’t have to take Plato’s word for it. A study in 2010 found that intermittent fasters experienced reductions in a number of biological indicators that suggest a diminished risk of developing chronic diseases such as type-2 diabetes. Two years later, a similar investigation produced evidence that the 5:2 diet may help lower the risk of certain obesity-related cancers such as breast cancer.

    The science behind intermittent fasting is simple: if you don’t consume enough energy, your body burns off your fat reserves. The more complex explanation is that regular intermittent fasting activates a gene called SIRT1, more commonly known as the ‘skinny gene’, which repairs cells during times of scarcity of nutrients. The average intermittent faster loses one pound a week.

    The 5:2 diet does, in truth, totally enervate its disciples. Restricting oneself to 500 calories a day is not easy — despite promises of three meals, it was preferable to stick to sushi for lunch and a bowl of baked beans for supper, washed down with endless glasses of tap water. I found myself eschewing all humans, all conversation, and any thought process that didn’t involve food, so obsessed did I become with the following day when I could eat normally again. Counting calories leaves one morose and forlorn. Life’s great pleasures are suddenly stripped away. But, lo, the weight fell off. Two days of pain began to seem like a reasonable sacrifice — particularly when one considers alternative restrictive options that dominate every day of the week.

    I’m not quite in Plato’s league yet — but I certainly felt better after the Christmas slump.

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