Certain practices may help support a safe fast. This includes staying hydrated and including enough protein in your meals on the days you eat.

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There are many different ways to fast.

Intermittent fasting is an increasingly popular eating pattern that 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 in 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 (5):

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

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 (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.

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.

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 (9).

Most health authorities recommend the 8×8 rule — eight 8-ounce glasses, or just under 2 liters (L) in total, of fluid every day — to stay hydrated (10).

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 (11).

During a fast, many people aim to drink more than 8 cups (2 L) 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.

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.

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. (12).

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 (13).

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

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 (7).

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 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 may help increase feelings of fullness (16).

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

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

Many 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.

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).

Some research also shows that many commercial diet plans are lacking in other important nutrients, including zinc, selenium, and vitamin E (21).

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 (22).

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 (6).

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 find it hard to exercise while fasting.

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
• individuals who are trying to conceive
• those who are pregnant or nursing
• people with underweight
• individuals who have experienced an eating disorder
• those who have problems with blood sugar regulation
• people with low blood pressure
• individuals taking prescription medications
• those with a history of amenorrhea
• older adults
• adolescents

While fasting can be healthy for many people, you should speak to a doctor first if you have certain medical conditions or are pregnant, breastfeeding or chestfeeding, 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.