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Intermittent fasting

6-minute read

Key facts

  • Intermittent fasting is a dietary trend that includes blocks of time when you eat normally and blocks of time when you don’t eat anything.
  • Types of intermittent fasting include when you only eat for a certain number of hours each day or when you eat small amounts of food for a few days a week and eat normally on other days.
  • Most people can try intermittent fasting, but it is not recommended for children, adolescents, people with an eating disorder, if you are pregnant or breastfeeding or if you have certain medical conditions.
  • While intermittent fasting can lead to weight loss, more research about other health benefits is needed.
  • It’s important to speak to your doctor before you start intermittent fasting, as your doctor will assess your general health and advise if it is a good option for you.

What is intermittent fasting?

Intermittent fasting is a dietary trend which involves you eating normally at specific times, while at other times you have low or no food intake. With intermittent fasting, there are no foods you should or shouldn’t eat, just rules around the timing or amount of eating. Intermittent fasting is also known as intermittent energy restriction.

How does intermittent fasting work?

When you are intermittent fasting, you have times where you don’t eat anything, which means that you are eating less food in a day or a week overall. During the times that you are eating, you should eat normally, with a focus on nutritious foods. You can drink water at any time, including when you are fasting.

Research into the other ways that intermittent fasting works, such as if it affects how your body processes energy while you are fasting, is being done. There are no conclusive results released on this yet.

What are examples of intermittent fasting?

There are many different ways you can do intermittent fasting. Different types include:

  • time restricted eating, such as the 16:8 plan when you eat for an 8-hour window in a day and then fast for the remaining 16 hours of the day
  • 5:2 diet, when you choose 2 days each week to have only a small amount of food, usually between 2000 and 3000 kilojoules, but eat normally the other 5 days
  • eat-stop-eat when you fast for 24 hours 1 or 2 days a week

Is intermittent fasting safe?

Intermittent fasting can be safe for some people, but it is not suitable for everyone.

Usually, you will feel hungry when you first start intermittent fasting and you may also experience headaches. Your body should become used to the intermittent fasting.

If you are feeling weak, anxious, irritable, unable to concentrate or unable to do you usual activities, stop intermittent fasting and speak to your doctor.

You may need to increase how much water you drink to make sure you don’t become dehydrated, as your body relies not only on water but also fluid from the food that you normally eat to keep hydrated.

If you fall into any of these groups you should not do intermittent fasting:

If you are having treatment for cancer or taking diabetes medicines, you should speak to your doctor to see if intermittent fasting is safe for you.

ASK YOUR DOCTOR — Preparing for an appointment? Use the Question Builder for general tips on what to ask your GP or specialist.

Are there any health benefits of intermittent fasting?

Most of the original research on intermittent fasting was done on animals, and many of the benefits that people claim have not been confirmed in humans. While more research is needed on the benefits of intermittent fasting, it seems that having regular meals and avoiding late night food or lots of snacks is good for your health.

Some research has shown that the benefits of intermittent fasting on your health and weight are due to eating fewer calories and that the timing of when you eat doesn’t make a difference.

Recent research in humans has found that while you may lose weight with intermittent fasting, you don’t get the same health benefits as other diets that reduce calories while still making sure that you get the nutrients you need. This may be because you are not getting enough of the right nutrients in your diet with intermittent fasting.

Other research has shown that only eating at certain times of the day can help with how your body processes sugar and your blood pressure, even if you are not eating less calories.

When should I see a doctor?

If you are considering intermittent fasting, you should see your doctor before you start, to make sure it’s right for you. They also may need to adjust your medicine doses if you have any.

If you are intermittent fasting, a dietitian can advise you about what foods you should eat to make sure that you are still getting all the nutrients you need.

To find a dietitian near you, use the healthdirect Service Finder tool.

FIND A HEALTH SERVICE — The Service Finder can help you find doctors, pharmacies, hospitals and other health services.

Resources and support

Dietitians Australia has advice about intermittent fasting as well as information on health benefits.

Diabetes Australia has information about intermittent fasting and if is right for your situation.

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available 24 hours a day, 7 days a week.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: February 2024

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