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Fasting: everything you need to know

Research shows that restricting calories and giving your body a break from food can boost health, protect against disease and help you lose weight. Read our complete guide to fasting....

Image: Maya Smend
Image: Maya Smend

When the concept of intermittent fasting went mainstream back in 2012 with the 5:2 diet, it was a spectacular overnight success. Who wouldn’t be seduced by the idea of boosting your health, slowing the ageing process, and losing weight while feasting on unlimited quantities of food and drink? The only caveat: you’d have to eat virtually nothing for two days each week. Millions figured two days of hunger were a just-about-tolerable sacrifice worth making in return for slender longevity.

Since then, study after study has proven the benefits of giving your body a break from food. Fasting is something we evolved to do: in ancient times food would be scarce and occasional hunger would be the norm. But in today’s world, where opportunities to eat present themselves continuously, you have to be pretty determined to endure sustained hunger for very long. That’s why intermittent fasting has been so successful – research increasingly shows it offers the same health benefits as full fasting, while allowing you to eat plenty of real food on non-fast days.

Dr Michael Mosley is often credited as being the ‘father of fasting’ because of the runaway success of his bestselling 5:2 diet book. But before he’d typed his first draft, there were other intermittent fasting plans already on the table. Back in 2009 Dr Krista Varady, a US nutritionist at the University of Illinois, published a study extolling the weight loss and heart-protecting benefits of ‘alternate day fasting’ where you eat 25% of your energy needs (500 cals for women, 600 for men) on your ‘fast’ day, then eat normally the next day. And closer to home, at Manchester University, a research dietitian called Dr Michelle Harvie found that intermittent fasting (specifically two days on 500 calories and five days on a strict Mediterranean diet) could reduce the risk and recurrence of breast cancer, and improve the chance of recovery.

Image: Maya Smend
Image: Maya Smend

How it works

At the cutting edge of research is Professor Valter Longo, a gerontologist at the University of Southern California. He regards fasting as ‘one of the most powerful interventions we can make to promote beneficial changes to our health’. ‘Fasting appears to awaken a highly coordinated response that is already built into the body but that has fallen dormant by generations that never seem to stop eating,’ he says. ‘It helps minimise disease and maximise a healthy lifespan because it acts on the ability of the body to regenerate and rejuvenate itself.’ By stopping eating, you give your body a break from food and allow it to switch priorities away from digestion and on to other important, disease-preventing functions, such as ‘autophagy’ (the process of clearing away old cells to make way for new ones).

This has a wide-reaching impact on many different areas of the body and brain. Studies show fasting improves the body’s ability to fight inflammation; it improves heart health (by lowering blood pressure, blood fats and cholesterol levels) and boosts brain function (improving memory and processing powers, and protecting against disorders like Parkinson’s and Alzheimer’s disease) and immunity (helping fight off cancers). It also increases levels of growth hormones (which aid repair of damaged tissues), reduces insulin resistance (the metabolic phenomenon which puts us at risk of type 2 diabetes) and generally extends our life expectancy. Oh and it can also be a useful way to shift excess weight if you need to.

Maintaining a healthy weight and a slim(ish) waist (ideally your waist measurement should be no more than half your height) is a scientifically proven way to reduce your cancer risk. That’s because obesity – and particularly tummy fat – is linked to many forms of cancer. The ‘visceral fat’ which builds in your abdomen appears to trigger the rapid dividing of cells making cancer of the breast, bowel, pancreas, oesophagus and gallbladder more likely. The good news is intermittent fasting appears to be a particularly effective way to lose abdominal fat. One study showed that the combination of weight loss and improved insulin sensitivity reduced breast cancer risk in pre-menopausal women. Another has shown that extending a nightly ‘fast’ for more than 13 hours could reduce the risk of breast cancer recurring by as much as 36 percent.

Image: Maya Smend
Image: Maya Smend

Is it right for you?

If, despite all the evidence, you are still put off by the thought of being hungry, it might be good to know that the latest incarnations of intermittent fasting claim to offer the same health benefits at 800 calories a day for two days a week, and trials have also shown how a more aggressive approach, 12-weeks at 800 calories a day, is effective enough to put type 2 diabetes into remission. Fasting isn’t for everyone, and it is certainly not suitable if you’re under 18, pregnant, unwell or underweight; fasting regimes can also feel restrictive and difficut to stick to.

But according to Dr Xand van Tulleken of Channel 4’s How To Lose Weight Well: ‘If you can manage to endure a fast, then they do seem to be an effective way to prevent weight gain and they are likely to have other health benefits as well.’ ‘All forms of fasting require reserves of willpower and this can be affected by stress and personality characteristics,’ says Dr Meg Arroll, co-author of The Shrinkology Solution (Quadrille, £9.99). ‘If you choose a fasting plan that suits your personality and lifestyle, this will improve your chance of sticking with it, and seeing health benefits.’

Which fast?

The 5:2: Eat no more than 500 cals a day, twice a week. Simple and flexible, you choose your own fast days. But 500 cals can feel restrictive and difficult to stick to.

Fast 800: Michael Mosley’s updated version of 5:2 advocating two days on 800 calories, and five on a lower carbohydrate regime. A more aggressive plan involves 800 calories a day for 12 weeks, for which you’ll need iron willpower.

Alternative Day Fasting: Eat 500 cals on one day, then eat normally the next. Restrictive, but simple and effective, for people who love consistency.

Time Restictive Eating: Eat within a strict window, thereby extending your nightly fast (12:12, 10:14, 8:16 or even 20:4). A gentle starter to intermittent fasting that can be as easy as skipping breakfast, and yields impressive results.

Fasting Mimicking Diet: Dr Valter Longo’s plan, which involves five days of fasting two or three times a year on a diet of 400 cals of veg and 400 cals of nuts/oil/seeds every day for five days. Research-backed, and effective in boosting health.

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