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Mind & Body

Everything you need to know about intermittent fasting

Can intermittent periods of running on empty have positive, long-lasting effects on our health? FIORELLA VALDESOLO asks the experts and breaks down the different methods


In 2018, Time magazine put together its first-ever list of the 50 most influential people in healthcare. On it, under the title “fasting evangelist”, was Dr Valter Longo. The ascribed label was apt: as the director of the University of Southern California’s Longevity Institute, Longo has spent decades researching the impact of calorie restriction on our overall health and is passionate about regular fasting as a means of activating the body’s metabolism, protecting against chronic diseases, lowering blood pressure and prolonging life span.

While fasting has been an integral part of certain cultures for centuries, mostly in a religious context as a form of cleansing, it has experienced a resurgence in recent years, thanks to a swell in scientific research around its benefits, proselytizing by public figures like Twitter’s Jack Dorsey, and the popularity of books by experts such as Longo, Dr. Jason Fung and Dr. Michael Mosley. Here are some rules of engagement to consider before you embark on a fast…

How does fasting impact the body?

What fasting does to the body is put it under a mild form of stress, forcing our cells to adapt by enhancing their ability to cope, says medical herbalist and nutrition coach Daniela Turley. “When we fast, the lack of glucose causes the body to make its own glucose,” explains Turley. “Because our bodies conserve energy during fasting, our basal metabolic rate becomes more efficient.” Further on in a fast cycle, a process called ketosis happens, when the body burns its primary power source of stored fat. While the effect of a fast on the body depends on the type of fast and the individual compliancy, there are a number of potential benefits, says Dr. Dana Cohen, a New York-based functional and integrative physician. It can spawn weight loss, decrease the production of free radicals and lessen the damage incurred from them, lower inflammatory markers and blood pressure, improve blood-sugar regulation and, with prolonged fasting, promote stem-cell regulation, says Cohen.

What are some of the different fasting approaches?

While adhering to a certain diet when intermittent fasting (wherein you fast for a specific stretch of time) isn’t often a hard-and-fast rule, it is more optimal if the food choices you’re making during your eating windows are healthy ones. Turley also advises having a doctor keep an eye on your bloodwork while fasting, as it can result in reduced thyroid hormones, low protein and low minerals. Here’s a quick primer on the various approaches…

The 12-hour method

This, says Cohen, is a great starting point for novice intermittent fasters, because it’s easy to adopt. People are required to limit their caloric intake to a 12-hour window, then fast for the remaining 12 hours. So, if you stop eating by 8pm, then you would wait until 8am to have breakfast. And, Cohen adds, for both this and the 16:8 method, you can drink non-caloric beverages (black coffee, black or herbal teas and water) during your fasting hours.

The 16:8 method

This popular approach requires that you eat your three daily meals within an 8-to-10-hour window, and fast for the remaining 14 to 16 hours. It’s most easily achieved by finishing your evening meal no later than 8pm and not eating again until noon the next day.

The 5:2 method

Five days of normal eating (and a reminder that this should ideally be a healthy diet) are bisected by two days of caloric restriction (usually 500 calories for women and 600 for men). Whether the two days of restrictive eating come one after the other is up to you, but, says Cohen, there may be more benefit, from a metabolic standpoint, to taking them consecutively.

The eat-stop-eat method

A far more extreme version of 5:2, in this approach your two days are not just caloric restriction, but total 24-hour fasts (save for water, black coffee and any other beverages without calories), which can be hard on your ability to function at an optimal level.

The alternate-day method

Another intense option, this fast requires people to restrict calories (to 500 total) every other day.

The spontaneous method

As the name implies, this approach – akin to increasingly popular Intuitive Eating methodology – suggests people simply skip a few meals a week when they’re not feeling hungry.

The ‘warrior’ method

The so-called Warrior Diet mimics many of the Paleo food choices and requires that you only eat small quantities of raw fruits and vegetables during the day, and then one larger meal in the evening.

Who shouldn’t fast?

Medical professionals agree that anyone who is considering embarking on a fast should consult their doctor first. Do not fast if you are pregnant or breastfeeding, have diabetes or a history of an eating disorder, and always seek professional medical guidance before making changes to your diet. Research has shown that daylight fasting can sometimes have a negative effect, particularly on decision-making abilities. “Brain inflammation is linked to poor memory and there is some evidence that fasting reduces cytokinesis. But, on the whole, fasts reduce cognitive function and working memory due to low glucose,” says Daniela Turley.

Always consult your physician or a medical professional before doing a fast or making any other changes to your diet

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