How to fast correctly

How to Fast Safely: 10 Helpful Tips

By Helen West, RD on January 2, 2019

There are many different ways to fast.

Intermittent fasting is an increasingly popular eating pattern which involves not eating or sharply restricting your food intake for certain periods of time.

This fasting method has been linked to a range of potential health benefits, including short-term increases in human growth hormone (HGH) and changes to gene expression (1, 2, 3, 4).

Such effects are linked to longevity and a lower risk of disease. Thus, people who fast regularly often hope to lose weight or live a healthier, longer life.

However, fasting can be dangerous if not done properly.

Here are 10 tips to help you fast safely.

1. Keep Fasting Periods Short

There is no single way to fast, meaning that the duration of your fast is up to you.

Popular regimens include:

• The 5:2 Pattern: Restrict your calorie intake for two days per week (500 calories per day for women and 600 for men).
• The 6:1 Pattern: This pattern is similar to the 5:2, but there’s only one day of reduced calorie intake instead of two.
• “Eat Stop Eat”: A 24-hour complete fast 1–2 times per week.
• The 16:8 Pattern: This pattern involves only consuming food in an eight-hour window and fasting for 16 hours a day, every day of the week.

Most of these regimens advise short fast periods of 8–24 hours. However, some people choose to undertake much longer fasts of 48 and even up to 72 hours.

Longer fast periods increase your risk of problems associated with fasting. This includes dehydration, irritability, mood changes, fainting, hunger, a lack of energy and being unable to focus (5, 6, 7).

The best way to avoid these side effects is to stick to shorter fasting periods of up to 24 hours — especially when you’re just starting out.

If you want to increase your fasting period to more than 72 hours, you should seek medical supervision.

Summary Longer periods of fasting increase your risk of side effects, such as dehydration, dizziness and fainting. To reduce your risk, keep your fasting periods short.

2. Eat a Small Amount on Fast Days

In general, fasting involves the removal of some or all food and drink for a period of time.

Although you can remove food altogether on fast days, some fasting patterns like the 5:2 diet allow you to consume up to around 25% of your calorie requirements in a day (8).

If you want to try fasting, restricting your calories so that you still eat small amounts on your fast days may be a safer option than doing a full-blown fast.

This approach may help reduce some of the risks associated with fasting, such as feeling faint, hungry and unfocused.

It may also make fasting more sustainable since you likely won’t feel as hungry (9).

Summary Eating a small amount on fast days rather than cutting out all food may reduce your risk of side effects and help keep hunger at bay.

3. Stay Hydrated

Mild dehydration can result in fatigue, dry mouth, thirst and headaches — so it’s vital to drink enough fluid on a fast (10).

Most health authorities recommend the 8×8 rule — eight 8-ounce glasses (just under 2 liters in total) of fluid every day — to stay hydrated (11).

However, the actual amount of fluid you need — although likely in this range — is quite individual.

Because you get around 20–30% of the fluid your body needs from food, it’s quite easy to get dehydrated while on a fast (12).

During a fast, many people aim to drink 8.5–13 cups (2–3 liters) of water over the course of the day. However, your thirst should tell you when you need to drink more, so listen to your body (13).

Summary As you meet some of your daily fluid needs through food, you can get dehydrated while fasting. To prevent this, listen to your body and drink when thirsty.

4. Go for Walks or Meditate

Avoiding eating on fast days can be difficult, especially if you are feeling bored and hungry.

One way to avoid unintentionally breaking your fast is to keep busy.

Activities that may distract you from hunger — but don’t use up too much energy — include walking and meditating.

However, any activity that’s calming and not too strenuous would keep your mind engaged. You could take a bath, read a book or listen to a podcast.

Summary Keeping busy with low-intensity activities, such as walking or meditating, may make your fast days easier.

5. Don’t Break Fasts With a Feast

It can be tempting after a period of restriction to celebrate by eating a huge meal.

However, breaking your fast with a feast could leave you feeling bloated and tired.

Additionally, if you want to lose weight, feasting may harm your long-term goals by slowing down or halting your weight loss.

Because your overall calorie quota impacts your weight, consuming excessive calories after a fast will reduce your calorie deficit.

The best way to break a fast is to continue eating normally and get back into your regular eating routine.

Summary If you eat an unusually large meal after your fast day, you may end up feeling tired and bloated. Try easing gently back into your normal food routine instead.

6. Stop Fasting If You Feel Unwell

During a fast, you may feel a little tired, hungry and irritable — but you should never feel unwell.

To keep yourself safe, especially if you are new to fasting, consider limiting your fast periods to 24 hours or fewer and keeping a snack on hand in case you start to feel faint or ill.

If you do become ill or are concerned about your health, make sure you stop fasting straight away.

Some signs that you should stop your fast and seek medical help include tiredness or weakness that prevents you from carrying out daily tasks, as well as unexpected feelings of sickness and discomfort (6).

Summary You may feel a little tired or irritable during your fast, but if you start to feel unwell, you should stop fasting immediately.

7. Eat Enough Protein

Many people start fasting as a way to try to lose weight.

However, being in a calorie deficit can cause you to lose muscle in addition to fat (14).

One way to minimize your muscle loss while fasting is to ensure you are eating enough protein on the days you eat (14, 15).

Additionally, if you are eating small amounts on fast days, including some protein could offer other benefits, including managing your hunger.

Some studies suggest that consuming around 30% of a meal’s calories from protein can significantly reduce your appetite (16).

Therefore, eating some protein on fast days could help offset some of fasting’s side effects.

Summary Having enough protein during your fast may help minimize muscle loss and keep your appetite in check.

8. Eat Plenty of Whole Foods on Non-Fasting Days

Most people who fast are trying to improve their health.

Even though fasting involves abstaining from food, it’s still important to maintain a healthy lifestyle on days when you are not fasting.

Healthy diets based on whole foods are linked to a wide range of health benefits, including a reduced risk of cancer, heart disease and other chronic illnesses (17, 18, 19).

You can make sure your diet remains healthy by choosing whole foods like meat, fish, eggs, vegetables, fruits and legumes when you eat.

Summary Eating whole foods when you aren’t fasting may improve your health and keep you well during a fast.

9. Consider Supplements

If you fast regularly, you may miss out on essential nutrients.

This is because regularly eating fewer calories makes it harder to meet your nutritional needs.

In fact, people following weight loss diets are more likely to be deficient in a number of essential nutrients like iron, calcium and vitamin B12 (20).

As such, those who fast regularly should consider taking a multivitamin for peace of mind and to help prevent deficiencies.

That said, it’s always best to get your nutrients from whole foods (21).

Summary Regular fasting may increase your risk of nutritional deficiencies, especially if you are in a calorie deficit. For this reason, some people choose to take a multivitamin.

10. Keep Exercise Mild

Some people find that they are able to maintain their regular exercise regimen while fasting (5).

However, if you’re new to fasting, it’s best to keep any exercise to a low intensity — especially at first — so you can see how you manage.

Low-intensity exercises could include walking, mild yoga, gentle stretching and housework.

Most importantly, listen to your body and rest if you struggle to exercise while fasting.

Summary Many people manage to participate in their regular exercise routine on fast days. However, when you’re new to fasting, it’s recommended to only do mild exercise to see how you feel.

Fasting Isn’t for Everyone

Although fasting for short periods is generally considered safe, the following populations shouldn’t attempt to fast without consulting a medical professional:

• People with a medical condition like heart disease or type 2 diabetes
• Women who are trying to conceive
• Women who are pregnant or breastfeeding
• People who are underweight
• Those who have experienced an eating disorder
• People who have problems with blood sugar regulation
• People with low blood pressure
• Those who are taking prescription medications
• Woman with a history of amenorrhea
• Older adults
• Adolescents

Summary While fasting can be healthy for many people, you should speak to your doctor first if you have certain medical conditions or are pregnant, breastfeeding or trying to conceive. Fasting is not recommended for people who have had an eating disorder.

The Bottom Line

Fasting is the practice of abstaining from food and beverages for extended periods. Depending on how it’s done, it may boost your health.

People may choose to fast for dietary, political or religious purposes. One popular method is intermittent fasting, in which you cycle between periods of eating and fasting.

To stay healthy while fasting, it’s best to keep fast periods short, avoid intensive exercise and stay hydrated.

Eating enough protein and keeping a balanced diet when you’re not fasting can also maintain overall health and ensure successful fasts.

5 Tips to Do It Safely – Cleveland Clinic

Just the thought of fasting may make you hungry. But going without food for a time — whether for health or religious reasons — can be good for you, says hepatologist Nizar Zein, MD. 

“There’s actually a range of ways to fast,” he says. “Sometimes, fasting means avoiding certain types of food, like carbohydrates or fats. Other times, it just means reducing calories overall. Then, there’s the type of fasting when you don’t eat (or sometimes drink) at all for a day or more.” 

Many religions promote some form of fasting as a spiritual exercise. And medical literature indicates fasting, in general, can: 

• Support weight loss. 
• Decrease inflammation from chronic conditions like arthritis. 
• Lower your blood pressure. 
• Lower your cholesterol. 

“There also are theories that periodic fasting may help you live longer, boost brain function and prevent neurodegenerative disease,” Dr. Zein notes. 

If you’re planning a fast in which you don’t eat at all, Dr. Zein recommends these five tips for maintaining your health and energy level. 

Cut back on food and drink gradually for several days — or even weeks — before your fast. Otherwise, abruptly beginning a fast will be a shock to your body.  

“Don’t eat three full meals a day with between-meal snacks and then suddenly stop eating one day,” Dr. Zein says. “If your body is used to regular refueling, you may have a hard time maintaining energy levels during a fast.” 

And keep your sugar intake low as you’re heading into a fast. Loading up on cookies and sweet tea before your fast isn’t a good idea. You may feel full and satisfied at first, but when your blood sugar plummets an hour or two later, you may become extremely hungry and weak. To have enough energy for the long haul, fill up on complex carbohydrates (like pasta, rice and potatoes) and protein (like meat and beans). 

Some religious fasts restrict all food and beverages, including water, as part of the observation. If, however, the guidelines for your fast allow for consumption of water, staying hydrated will help you avoid dehydration, maintain your energy levels and lessen side effects like headaches, cramps and irritability.   

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“It’s not a good idea to do intense exercise when you’re not eating or drinking,” says Dr. Zein. “If you’re not planning to replenish nutrients for a while, preserve your energy for vital daily activities.” 

Before fasting, talk to your doctor about how to take your medications. Some medications — such as for seizure disorders — are essential, and you shouldn’t stop taking them while fasting. Other medications should be taken with food. “When people have adverse outcomes from fasting, it’s often because they didn’t take their medications correctly,” states Dr. Zein. 

At the end of your fast, replenish your calories gradually. Rather than going on an eating binge right away, spread those calories over your next two meals. This is better because it will help you avoid rapid changes in blood sugar and the fatigue associated with consuming a large amount of food. 

“Overall, fasting can be a healthy practice that I recommend for many people,” says Dr. Zein. 

Even when following these tips, too much fasting can be dangerous, though, and fasting for too long may cause dehydration, mental stress and disrupted sleep. Also, there are different health benefits and risks associated with various kinds of fasts, based on what restrictions you’re following and for how long. 

It’s customary in some religions to fast entirely for a day, for a portion of certain days or to abstain from certain foods for an extended period of time.

Is it safe? Research shows that religious fasting has potential benefits for improving cholesterol, reducing oxidative stress and balancing energy. 

Some diets recommend eliminating certain foods or restricting eating at certain times, both of which can be done in a healthy way, Dr. Zein says. 

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Intermittent fasting, for example, encourages people to only eat during certain times of the day or to restrict eating on certain days. It’s an eating pattern that focuses on consciously cutting back on calories for certain time periods. 

Certain restrictive diets, like the ketogenic diet (keto), approach fasting differently. Rather than fasting for a period of time, people who follow keto cut all carbs and sugars from their diets.   

Is it safe? Studies have shown intermittent fasting and certain restrictive diets can be good for your heart health, help with weight loss and improve your cholesterol. However, researchers also caution that fasting diets can be difficult to maintain as a long-term lifestyle.   

While fasting can be done safely for some people, it can cause problems for people with certain health conditions. 

Many religions indicate certain groups of people may not be required to participate in fasting based on certain criteria. From a health perspective, Dr. Zein suggests those who shouldn’t fast from all food and drink include people who: 

• Have diabetes and struggle with keeping blood sugar stable.  
• Have chronic kidney disease. 
• Are breastfeeding (chestfeeding). 
• Are underweight. 
• Are recovering from surgery or illness. 
• Live with or are at high risk for an eating disorder. 

Fasting may provide psychological and physical benefits when done in a healthy way. If you plan to make fasting a part of your routine, talk with a healthcare provider about any risks. 

Benefits, methods and rules of one-day fasting.

Table of contents

• Benefits of a hunger strike
• Varieties
• How to get into fasting
• Secrets of fasting
• Way out of a hunger strike

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