10 things you should know before you try intermittent fasting

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There are some important things to know before trying intermittent fasting.

Intermittent fasting is something you’ve probably heard an earful about this year. And its newfound popularity is proving that the buzzy fasting approach is going to hang around for a while, as it already has tons of celebrity enthusiasts and a very active subreddit with up to 137k subscribers.

But if you are curious as to what intermittent fasting actually is, registered dietitian Abbey Sharpe explained to INSIDER some of the ins and outs. Basically, it involves eating only during certain parts of the day, while abstaining from anything but water and coffee for the rest of the time. 

However, to give you the full breakdown on everything intermittent fasting, we spoke to Sharpe and registered dietitian Sylvia North about some of the advantages (and disadvantages) to consider if you are planning on giving intermittent fasting a try. Below are some expert tips on the subject to totally keep in mind.

Intermittent fasting can promote weight loss, but it might be short-term.

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It may not last.

"I don’t really like seeing weight loss as a benefit across the board, but I know this is the number one reason why people are trying intermittent fasting," Sharpe told INSIDER.

However, she suggested that several human studies have found that intermittent fasting has been associated with a significant decrease in body weight, body fat, and waist circumference in the short term, making it something to consider if you are giving intermittent fasting a try.

Fasting can be pretty simple and can fit easily into your routine.

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It can work well with some people's routines.

"This eating pattern is easily implemented and great for people who like routine," Sharpe said. It also means you don’t have to cut out specific types of foods that you may enjoy, she suggested.

Intermittent fasting can have a positive impact on your cholesterol levels.

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It may decrease your blood pressure.
Lucy Nicholson/Reuters

Sharpe suggested that intermittent fasting may also lead to significant decreases in total cholesterol, LDL (bad cholesterol), blood pressure, and triglyceride levels. Reducing these markers may help reduce the risk of cardiovascular disease, she explained.

Intermittent fasting can improve your blood sugar levels.

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It depends on the individual.
Flickr/Andrey Filippov

Sharpe explained that some research has suggested that intermittent fasting improves insulin sensitivity in some individuals. A 2017 review found that intermittent fasting reduced a percentage of body fat (and HbA1C) compared to a continuous energy restriction diet, she said.

Intermittent fasting can have some negative side effects worth looking into.

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It may cause headaches.
Patrick Denker / Flickr

"A few studies have found that intermittent fasting can result in some undesirable side effects like lack of energy, bad temper, headaches, constipation, and lack of concentration," Sharpe said. She also suggested that people with digestion problems may experience cramping, abdominal pain, and bloating when larger portioned meals are consumed in a short amount of time.

You’ll want to avoid intermittent fasting if you are diabetic or have struggled with an eating disorder.

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It can have a negative impact on your health or eating patterns.

"You’ll want to avoid intermittent fasting if you have diabetes (or high blood sugar) and need a steady stream of energy throughout the day to balance blood sugar levels," Sharpe said. Also, if you have ever had a history of disordered eating, she explained that intermittent fasting may exacerbate potential eating patterns such as a binge-eating mentality or a restrictive mindset.

It’s important to eat a balanced diet when fasting.

A balanced diet is still important.
Flickr/Marco Verch

"Remember that during your feasting periods you need to eat a balanced diet," Sharpe recommended. It doesn’t just matter how many calories you are consuming, she said, but also where those calories are coming from. If you decide to try intermittent fasting, she advised speaking with a registered dietitian for personalized advice and supervision.

There are several types of fasting to try.

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There are a few types to try.
Chris Urie

North suggested that there are many different forms and styles of intermittent fasting to try. Short fasting, she explained, may last from anywhere from 14-24 hours, and can be followed regularly (weekly to daily) by people who are accustomed to a low-carb, healthy fat, or ketogenic lifestyle.

Long fasting, she suggested, usually lasts three to five days, and is not done as frequently as shorter fasts. This kind of fast, she said, may usually only be considered for specific medical or health goals under the guidance of a professional.

Older adults and pregnant women shouldn’t try intermittent fasting.

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It may not be safe.

"Fasting is not recommended for pregnant, breastfeeding women, or children under the age of 18, as this isn’t the right life stage to be fasting," North said. Older adults (or people with diagnosed medical conditions) she added, also should not fast, as she explained this often suggests a risk of malnutrition, unintentional weight loss, poor oral intake, or low body weight.


Start off slow if you are new to intermittent fasting.

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Start gradually.

"I generally recommend people wanting to experiment with fasting to start having a later breakfast on two to three mornings a week," North advised. This is very natural for many people, she said and is very easy for them to get their heads around.

You’ll want to watch your stress levels when you are fasting.

There are plenty of ways to do this.
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"Watch your overall stress levels when you are fasting," North suggested. Sometimes, adding the pressure of fasting while there are other external stressors to be concerned about can lead things to go sideways, she advised.

Add plenty of water and diet to your diet while fasting.

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Hydration is important.

North also advised drinking plenty of water and adding salt to your diet with fasting. Sucking on pieces of flaky salt can help if you get a headache, she recommended.

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SEE ALSO: Here's what you need to know about the different types of 'intermittent fasting' and their benefits

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