What is intermittent fasting?

Intermittent fasting is a dietary trend that involves limiting your eating to specific times. If you are intermittent fasting, there are specific times when you eat normally. At other times, you eat little or no food.

With intermittent fasting, there are no foods you should or should not eat. There are only rules around the timing or amount of food you eat. Intermittent fasting is also known as intermittent energy restriction.

How does intermittent fasting work?

When you are intermittent fasting, you have times when you do not eat (fast). 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.

This usually means that you are eating less food in a day or a week overall. By fasting, you are reducing the number of calories that you consume each day.

Intermittent fasting may help the body burn fat by turning fat into ketones. Overall, it can lead to weight loss and is linked to better cholesterol levels and lower blood pressure.

There is research being done into the other ways that intermittent fasting affects your body. It may influence your metabolism and how your body processes energy. There are no conclusive results on this yet.

What are examples of intermittent fasting?

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

• Time restricted eating — a daily pattern of eating and fasting windows. This includes the 16:8 plan, where 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 or alternate day fasting — when you fast for 24 hours 1 or 2 days a week and eat freely the rest of the time.

Is intermittent fasting safe?

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

When you first start intermittent fasting, you will feel hungry. You may also experience headaches. Your body is likely to become used to intermittent fasting over time.

Stop intermittent fasting and speak to your doctor if you are:

• feeling weak, anxious or irritable
• unable to concentrate
• unable to do your usual activities

You may need to increase how much water you drink to make sure you do not become dehydrated. Your body relies not only on water but also on fluids from the food that you normally eat to stay hydrated.

How do I know if intermittent fasting is safe for me?

Intermittent fasting is not safe for everyone. You should not do intermittent fasting if you:

• are underweight
• have, or have previously had, an eating disorder
• are pregnant or breastfeeding
• are a child or teenager
• are an older adult
• take daily medicine that must be taken with food

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

What are the health benefits of intermittent fasting?

More research is needed on the health benefits of intermittent fasting. Many of the benefits that people claim about intermittent fasting have not been confirmed in studies on humans. Most of the original research on intermittent fasting was done on animals. However, 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. The timing of when you eat may not make a difference.

Recent research in humans has found that although you may lose weight with intermittent fasting, you do not get the same health benefits as you do from some other diets. Diets that reduce calories while still making sure that you get the nutrients you need can provide more health benefits. 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 fewer calories. Intermittent fasting may improve your metabolism and in turn reduce your risk of cardiovascular and metabolic diseases.

When should I see a doctor?

If you are considering intermittent fasting, you should see your doctor before you start, to make sure it is right for you. They may also need to adjust your medicine doses if you take regular medicines.

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.

Resources and support

If you are worried about your diet or weight, you should talk to your doctor or dietitian.

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

Diabetes Australia has information about intermittent fasting to help you know if it is right for your situation.

Health WA has a resource for evaluating dietary advice.

To make sure you are eating enough food to get the nutrients you need, check the Australian Dietary Guidelines.

Get Healthy NSW is a free telephone service that is available in NSW. It is staffed by qualified health coaches who support adults to make lifestyle changes regarding healthy eating, physical activity and reaching and/or maintaining a healthy weight.

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