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.
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.
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 (, , ).
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.
In general, fasting involves the removal of some or all food and drink for a period of time.
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.
Most health authorities recommend the 8x8 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 ().
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.
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.
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.
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.
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 ().
Summary You may feel a little tired or irritable during your fast, but if you start to feel unwell, you should stop fasting immediately.
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).
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.
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.
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.
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 ().
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 ().
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.
Some people find that they are able to maintain their regular exercise regimen while fasting ().
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.
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
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.
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.