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What is intermittent fasting? - Intermittent fasting is a broad term encompassing various eating schedules, all cycling between a period of fasting and non-fasting over a defined period. It commonly involves daily 16-hour fasts and 8 hours of eating, called 16/8.

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There are a few variations - There is also the 5:2 diet, in which you consume only 500-600 calories two days of the week, and eat normally the other five days.

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Weight loss - IF initially became popular for weight loss. One of the guiding theories is that, along with a calorie reduction, IF can help decrease appetite by slowing the body's metabolism.

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Other benefits - Many also argue that research suggests IF reduces inflammation, balances blood sugar, enhances cell repair, and could increase longevity.

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No strong evidence - A paper in Harvard Health Publishing says that though it's true shedding excess fat will improve a person's metabolic profile and lower cardiovascular risk, there's still no strong evidence.

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You don’t have to count calories - This diet is so attractive because it’s seen as saving both money and time, and it also doesn’t specify which foods you should eat but rather when you should eat them.

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Controversial takes - Some people believe that IF was just made up by millennials who wanted to make themselves feel better about having to skip meals, while others believe it's just a cleverly disguised and socially acceptable form of anorexia.

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Research isn’t as extensive as people think - Many sources claim research “suggests” various benefits, but Harvard Health Publishing stated in 2019 that the studies have been short and limited, and IF has not shown drastically different results compared to normal daily restricting of calories.

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Kourtney Kardashian - In 2018, Kourtney Kardashian said she's a fan of IF on her app, explaining she wouldn't eat after 7 pm, and would eat breakfast after her workout, around 10:30 am.

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Justin Theroux - The actor's trainer reportedly had him eating only between 7 am and 7 pm for a few weeks. 

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Halle Berry - In 2018, Halle Berry revealed her love for IF on Instagram. Speaking with her personal trainer, she said that she usually eats breakfast around 2 pm, but that she's supplementing her vitamins and nutrients.

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Hugh Jackman - The actor has reportedly long been doing a 16-hour fasting period, followed by eight hours where he'll eat.

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Scarlett Johansson - For her role as Black Widow, the actress' trainer told Harper's Bazaar that she fasted for around 12 hours each day, and pushed it to 14 or 15 hours depending on her work schedule.

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Reese Witherspoon - Witherspoon told Radio Times in 2019 that, like her 'Morning Show' co-star Jennifer Aniston, she only consumes coffee and green juice in the mornings.

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Terry Crews - The fit actor has long been a supporter of IF. He reportedly starts his day at 4:45 am, works out at 6 am, and doesn't eat until 2 pm, explaining that he drinks four to five bottles of water with amino acids in that time period.

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Vanessa Hudgens - In 2019, actress Vanessa Hudgens revealed that she's a fan of the 16/8 variation, telling Popsugar that she felt clearer and more energized when she stared, but also adding, "It's rough, it's no joke. I'm not gonna lie and say it's easy."

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Benedict Cumberbatch - The actor follows the 5:2 diet, meaning two days a week he eats only about 500-600 calories.

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Mindy Kaling - The hilarious actress has apparently tried IF, tweeting in 2018: "16:8 more like 16 hate."

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Jack Dorsey - The Twitter CEO took things too far for many people, only eating one very basic meal a day between 6:30 and 9:30 pm, and fasting the whole weekend. Many said this wasn’t wellness, but rather an eating disorder.

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Not sustainable long-term - Many people find they feel great at first, but struggle after a little while. IF is not recommended as a long-term diet, and it has the potential to mess up your fitness journey.

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Celeb nutritionists have weighed in - "Intermittent fasting supports metabolic markers," celebrity nutritionist Kelly LeVeque told E! News, "it lowers glucose, insulin, triglycerides and increases insulin sensitivity."

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Why celebrities love it but you probably won’t - Unless you're trying IF with professional assistance (a personal chef, nutritionist, etc.) to plan well-balanced meals, you're unlikely to hit your daily nutritional needs.

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If you want to try it, you have to start slow - First and foremost, consult a doctor to make sure this is a viable option for you. Then, start by eating your dinners earlier, or delaying breakfast a few days of the week.

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You can’t actually eat whatever you want - To get the benefits of IF, it’s even more important to eat nutritious food. Breaking a fast with unhealthy, high glycemic foods causes a higher increase in inflammatory markers and blood sugar, AKA the opposite of what IF boasts.

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You risk losing touch with hunger/fullness cues - According to Shape, many people who try IF start to lose touch with their hunger and fullness cues, making it difficult to establish an overall healthy diet in the long-term.

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You risk going overboard - When you starve yourself, many turn to rewards. So, on the 5-2 plan, people eat more than normal on non-fasting days. Many also turn to binge-eating, since appetite hormones in your brain reportedly go into overdrive when you're deprived of food.

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Consider your schedule - If you go to bed late every night, fasting starting at 6 pm isn’t a good idea. Consider when you get hungry, when you work out, your social life, work schedule, etc.

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Have an exit strategy - Nutritionists recommend that if you're serious about trying IF in a healthy way, have a plan, perhaps drawn up with a dietitian, so you have something to guide you.

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It’s just not for everyone -

Celeb nutritionist LeVeque warns, "It is not for everybody and you don't want it to get out of hand," adding that extreme IF can create eating disorders, food anxiety, and binge eating.

See also: Get in shape in 30 days with these 7-minute workouts.

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