Keto Diet App - Free Download Keto Diet App - Free Download
Take the guesswork out of following a low-carb diet, lose body fat & feel great!
KetoDiet app is FREE to download!

Practical Guide to Fasting

4.7 stars, average of 70 ratings

This post may contain affiliate links, see our disclaimer.
Expert ArticleEvidence Based

Practical Guide to FastingShareFollow us 261.1k

Quick Summary tl;dr

The benefits of fasting to both the body and the brain are becoming more apparent in both anecdotal and clinical data. There are various ways in which someone can incorporate fasting into their diet. The important point with this is to choose an approach that works for you and your body. It is also important to point out that not everyone needs to fast as well. Simply following intuitive eating of when you are and aren’t hungry is of great benefit to your body.

Become mindful of the way that you are eating to work out if it is true hunger or not.

Before starting any type of extended fast, you should always consult with your doctor, especially if you are on medication.

To really see the added benefits of fasting I would also recommend that your feeding days are based on real foods in their whole form as much as possible.

Table of Contents

The benefits of fasting to both the body and the mind are becoming more and more apparent. Who should and should not fast and what type of fasting should be done will vary depending on the individual.

What are the Main Forms of Fasting?

With the increase in popularity in fasting, there have been several different variations of the diet presented. The key to working out which will be best for you is to listen to your body.

1. The 16/8 Approach

This approach is something that people will follow daily. It focuses on having an eating window of 8 hours followed by 16 hours of a fasting window. This can look like people eating between the hours of 12-8pm or 11am-7pm and then not eating for the remaining hours. The major emphasis with this type of fasting is to make sure that there is a consistent window of not eating.

Many find it easier and more natural to simply skip breakfast and have their dinner as their last food intake. There have been some studies that have shown that eating later at night can cause a higher insulin response which can then promote greater fat storage ( 1). The link is believed to be due to the body’s circadian rhythm and so eating your last meal no later than 8pm (essentially before sun down) may be a good strategy if you’re struggling with weight loss.

Practical Guide to Fasting

With this type of fasting, it is important to eat a healthy diet during your eating window. Many find that eating a low carbohydrate way provides the optimal results.

During the fasting window, you can consume beverages including water, tea and coffee. Bone broth is also allowed and is often encouraged in longer fasts due to its mineral content.

For those that may find fasting for a longer period too difficult, this approach would work a lot better for them. Often females can find it a little difficult to fast beyond the 16 hours mainly due to hormonal factors.

The 16/8 window can also be adjusted to include longer periods of fasting and a shorted feeding window such as 18/6 or 20/4.

Suitable For

  • Those just starting out or new to fasting
  • People who are following a low carb or ketogenic diet already
  • Those with previous histories of eating disorders
  • Those that find fasting for longer than 16 hours too difficult

2. The 5:2 Fasting Diet

This form of fasting was developed by British doctor and journalist, Dr Michael Mosley. The ethos of the diet is looking to eat normally for 5 days and then fasting for the other 2 within the week.

One of the major differences of this approach to other forms of fasting, is that on the fasting days, they allow between 500-600 kcal to be consumed. For women, it is recommended to have 500 kcal and men to have 600 kcal, which are to be split between breakfast and dinner.

Their rationale for this approach is they feel this is one of the most sustainable ways to do fasting that will still allow you to be involved in social settings such as family meals.

There are however no strict guidelines of when or how you can distribute the calories within the day. You could opt to have two meals, three meals, two meals with a snack in between or even have it as one large meal.

On the fast days, there are two principles that must be followed when choosing what you can and cannot have to eat. That is to select foods that are both higher in protein and foods with a low glycemic index (≤50).

On the non-fasting days, they also advise that people can pretty much eat what they would like. I would still encourage people to eat a diet that is based in low refined sugar and grains to get the optimal health benefits.

This type of fasting therefore may be of more benefit to those individuals who suffer from disordered eating such as  orthorexia or binge eating disorder.

Once you reach your desired weight or health goal, you can then enter the maintenance phase. This sees your fasting days coming down to just once a week rather than twice a week.

Suitable For

  • Those who want to experiment a little more with fasting but not doing a full fast
  • Those who feel eating nothing within a certain period is not suitable for them
  • People who are not following a strict ketogenic diet or looking to have a little more food freedom

Practical Guide to Fasting

3. 24-Hour Fasting

This form of fasting involves you completely abstaining from food for a period of 24 hours. It is recommended you do this once to twice a week to see the benefits. Once you have been doing this form of fasting for a little while, then going to a 24-hour fast on alternative days can also be of benefit. I would however, not recommend this to those just starting out with fasting.

To start the fast, you choose a mealtime that you would like to end on. For example, if you have dinner at 7pm, then you would not eat anything again until 7pm the next again day. The same would be true if you were doing this from breakfast or lunch as well.

On the fast days you can have water, black coffee, tea and herbal teas. You can’t have any other form of food or calories within this time frame.

On the non-fasting days, it is important to make sure that you eat as you normally would. Make sure that you do not under eat, especially if you are a doing a 24 hour fast a couple of times a week. Many people think that to maximise weight loss, that they will just under eat on their non-fasting days. This can be counter-intuitive as the body will simply think that it is not getting the nutrients it needs and put itself into survival mode. Essentially it will hold onto, rather than burn any body fat stores.

Going straight into a 24 hour fast can sometimes be a little too much for people. You could always start off with a 16/8 and then work up from there to eventually get to the 24-hour window.

Suitable For

  • People looking to experiment a little more with fasting after trying 16/8 etc.
  • Those who feel comfortable with fasting and think this would fit in nicely with their lifestyle.

4. Extended Fasting

This type of fasting has gotten a lot more popular over the past few years. It involves individuals fasting for longer periods of consecutive time. The starting point for this is 2-3 days of consecutive fasting. For those that may struggle with the consecutive days, then fasting every other day can be done.

Other extended fasting includes fasting for a period of 5-7 days or longer. Many of the longevity and anti-ageing studies in mice has included this extended period ( 2). There still lacks any robust human data to show that extended fasting is needed or warranted. However, from preliminary data, fasting has been shown to help with regards to cancer prevention and ant-ageing.

For anyone considering longer term fasts, they should consult with their doctor especially if they are on any form of medication.

Some physicians have reported using this type of fasting for those individuals with severe obesity and insulin resistance. In the clinic of Dr Jason Fung, he has reported having some of his patients fast for a period of 30 days. It is extremely important to note here that all his patients are medically supervised.

On the days that you are fasting no food should be consumed. However, hydration is extremely important as is obtaining the necessary minerals. Water, tea and coffee is allowed ad hoc and bone broth is actively encouraged to drink to get the minerals and especially the sodium needed to avoid dehydration.

Suitable For

  • Those with extreme obesity or insulin resistance
  • People who can follow this under the care of a physician

Practical Guide to Fasting

5. No Rules Fasting

This type of fasting is where you are more listening to what your body is saying than following any set forms off guidelines.

If for example you wake up in the morning and don’t feel hungry, then skip having your breakfast at that time. Likewise, if you find that your body is signalling to you that you are hungry then eat!

Fasting can really be as simple as that. Contrary to popular belief as well, skipping the odd meal will not result in your metabolism slowing down or losing muscle mass. You do need to make sure that when you are fuelling your body that you are doing it the right way. If you scrimp on the calories at meal times, then your metabolism and muscle mass could be effected.

Most people who are following a ketogenic diet and are fat adapted find that this type of fasting happens quite naturally.

This is also great for those people who may have suffered from eating disorders in the past. Not having to specifically schedule in fasting times means that any obsession around food should not occur.

Suitable For

  • Anyone can follow this approach as it is more based on intuitive eating

Who Should Avoid Fasting?

Although there does appear to be many benefits to fasting, there are a group of people that should not be following fasting.

Type 1 Diabetics

Fasting will cause the bodies blood sugar levels to naturally drop. Those with type 1 diabetes could end up having their blood sugar levels drop too low, resulting in hypoglycaemia.

Those who are on insulin or insulin lowering drugs, will need to consult with a doctor before starting any type of fasting as the dose may need to be lowered.

Practical Guide to Fasting

Adrenal and Thyroid Issues

If you are someone that suffers from adrenal fatigue or any thyroid related issue, then it would be advisable to approach fasting with caution. People who have issues with either of these glands, have issues in the body when dealing with stress. Fasting is perceived as a stress to the body and so it could exacerbate any pre-existing condition.

Eating Disorders

People who are or have a history of eating disorders may find that fasting can exacerbate the disorders. If you have suffered with disordered eating then it would be advisable to start with the shorter term fasting such as the 16:8. Any long-term fasting should be avoided.


Anyone under the age of 18 should not fast. People this age are still growing and so require the adequate nutrients daily to suffice this.

Underweight or Undernourished

For those who have a BMI of 18 kg/m₂ or less, they would not be recommended to fast. There could be the risk that they end up becoming more undernourished.

Pregnant and Breastfeeding

Any female who is pregnant or breastfeeding should not undertake any type of fasting.

Like with children, women who are pregnant or breastfeeding require extra energy and nutrients for the growth of the baby and milk production.

Males vs Females

There is no data to say that males or females should not undertake fasting. However, case reports have shown that men appear to find fasting, especially extended fasting a little easier.

What Should You Eat on Your Non-Fasting Days?

Some fasting experts state that they don’t care so much about what you eat on the non-fasting days, it is more important to simply stick to the fasting days. The argument could be that knowing that you can eat anything that you would like on the non-fasting days, psychologically will help you through the fasting days.

It was believed that people who fast, would over compensate the next again day by eating more calories than they normally would due to increased appetite. However, a study looking at alternative day fasting found no significant increase in appetite. Participants on the feeding days also only ate 95% of their recommended calorie intake ( 3).

It is not recommended however, that you simply gorge on all and any food on the feed days. Your first meal after your fast, should be one of a normal size for you.

From case reports and anecdotal evidence, following the principles of a low carbohydrate, healthy fat diet, has been shown to offer added benefits to the goals of fasting.

Do you skip meals? All low-carb recipes in this list are suitable for intermittent fasting. They are nutrient-dense and contain 600-900 kcal per serving. They are ideal for those who eat only twice a day.

Practical Guide to Fasting

How to Fit Fasting into Your Lifestyle?

As with any dietary changes that you make, for them to be sustainable they really need to fit into your overall lifestyle. The same will remain true for fasting.

The first aspect to look at will be the type of fasting that is better for you. If you have a lot of social engagements, eat out a lot or train heavily, then doing more of the shorter or 16/8 type of fasting may be better for you.

If you have no underlying medical conditions and don’t have any of the above contraindications then there are no constraints on when you can start. If you are looking at one of the longer fasts though I would still recommend that you consult your doctor or at least get advice from a practitioner who knows what they are doing.

Before starting with fasting, you need to make sure that you are mentally prepared. You need to be feeling calm, purposeful and confident before starting with this.

Again, with the timings of the fasting, you need to find what works for you. If you prefer having breakfast with the family, then move your first meal to be at that time. Or if you don’t feel hungry first thing in the morning then skip it until later in the day.

How to Cope with Hunger When Fasting

If your form of fasting is that of 16/8 then you should find that hunger isn’t much of an issue. As you progress into the longer fasting and if you are starting it for the first time, you may notice some more hunger.

The first thing is to determine if it is true hunger or not. The way in which we as humans eat is to do with both hedonic and homeostatic ways of eating. Homeostatic eating is our true hunger, when the body needs to get its nutrients in. Hedonic way of eating is much more based on our emotions. We often eat for reasons such as boredom, tiredness or just to make us feel good.

Sometimes we feel hungry out of habit as well. If we are used to eating at a certain time then our bodies can get used to this pattern and signal for us to eat at these times.

On fast days try some of these tricks to help win at the hunger games:

Drink Water

If you’re feeling a hunger pang come on, try having some water. We can often mistake hunger for thirst.

Drink Bone Broth

Take in some bone broth - sometimes the hunger can stem from a depletion in electrolytes. The bone broth will help to replenish anything that is lost.


This may sound like common sense but the more you distract yourself from not thinking about food, the less hungry you should feel.

Journal it Out

To establish if you are eating for true hunger or more pleasure, try and get mindful around this. If you feel like you are craving a certain food, is it because of a particular emotion like boredom or sadness or due to habit.

Other FAQ’s on Fasting

1. Do you need to take any form of supplements?

For the shorter types of fasting you shouldn’t require any type of supplements. As long as you are eating well and properly on your non-fasting days then your body will be getting the nutrients it needs. On the extended fasting, you may find that you need to take a standard multi-vitamin to ensure you are getting all the vitamins and minerals you need. Do check with your supplements though as many of them do require you to take them alongside some food.

2. What about exercise and fasting?

With the 16/8 and the 5:2 form of fasting, you will find that fitting in exercise won’t be any different.

A lot of people find fasted exercise a lot more beneficial for maximum fat burning, especially fasted cardio work. This will vary from person to person though and you really need to listen to what your body is saying.

If you are doing a 24 hour or extended fast then I would recommend not training on these days, especially not heavy or explosive training.

Practical Guide to Fasting

3. Should you avoid alcohol?

If your overall goal of following a low carb diet and/or fasting is that of weight loss, then I would recommend that you abstain from alcohol altogether. If you are doing this for health benefits or in a maintenance phase then having a small amount of alcohol on your non-fast days would be ok. Do not consume alcohol on your fast days though, stick to only water, tea, coffee or bone broth for your liquid intake.

Do you like this post? Share it with your friends! 

Emily Maguire, BSc, MSc
Creator of

Emily Maguire

After completion of her BSc in Nutrition, Emily went onto study for an MSc in Obesity Science and Management. Author at, she is keen to share the myths and truths surrounding the ever confusing and interesting topic of nutrition.

With over 7 years of experience working within the commercial weight loss sector, she has unprecedented insight knowledge into the use of alternative nutritional therapies, particularly that of the ketogenic diet.

Expert Article

This article was written by Emily Maguire, BSc, MSc who is a qualified expert. At KetoDiet we work with a team of health professionals to ensure accurate and up-to-date information. You can find out more on the About us page.

Evidence Based

Evidence-Based articles are based on medical research, and scientific evidence. Our expert authors focus on hard evidence alone and include relevant research references from trusted sources to support their articles. We always aim to deliver relevant, trustworthy and up-to-date information based on trusted evidence and proven research.

Let us know what you think, rate this post!

Leave a comment

Note: Any links to products or affiliate links will not be approved.
Please note that we do not offer personalised advice. For any diet related questions, please join our Facebook community.

Comments (18)

"If you are doing a 24 hour or extended fast then I would recommend not training on these days, especially not heavy or explosive training."
I think working out during fasting is similar to working out on a keto diet.  When you first start, it will be hard because your body is looking for glycogen, especially for high intensity training, so take it easy while your body adapts.  Once you are fat-adapted, there should not be any issues with working out while fasted, as long as you have body fat to burn.
Do you have any reference studies showing that woman aren't as good at fasting? From what I've seen from Dr. Jason Fung, this is not true.

Thank you for the valuable information above.  I was wondering about the coffee during fasting hours - 18/6 approach - is it ok to have butter or ghee in the coffee with stevia drops or do you need to drink it black?  Does it negate the purpose of fasting?  Please let me know. Tina

Hi Tina, it depends. Strictly speaking, anything above 50 kcal is not considered fasting. Some people recommend BPC while others avoid it during the fasting window. Here's more about it (search for "BPC" in the post): How To Low Carb: 15+ Common Weight Loss Mistakes

I started doing 16/8 a month and a half ago. Since then time just flies by and suddenly it’s been 20 hours or 24 hours. This happens everyday. So I’ve started doing OMAD. During that meal I try to get in ALL my macros, meeting my protein and trying to meet my fats. Sometimes coming in a little short on calories but nothing too bad. I find this way of eating SO much easier. Trying to balance my keto macros while eating at work was very difficult.

Hi Kat,
Thank you for sharing this. It really is about doing what works for you and for your body as well. Glad you have found what works for you!

Hello. I downloaded the sample of this cookbook on Amazon hoping it'd show the recipes in the book. A list of the recipes (index or table of contents). But this was not included. Is it possible to get this prior to purchasing?

Hello Jenn, which cookbook are you referring to? I created 4 cookbooks. Thanks!

Great information! Thank you!

Thank you Lynne

I love how you break this down. Fasting can seem confusing sometimes because there are so many different options and each has different complexities.

Hi Vince,
Thank you so much for your comment, it can get a little confusing sometimes, glad this helped.

I am looking for a dietician/nutritionist who is knowledgable of a LCHF style of nutrition.
I live in Toronto, Canada.  Do you know anyone or you know how can I find one?

Hi Liliana,
I am sure Martina has a list of experts on her site. Are you looking for someone local or someone you can work with online?

Dr. Fung seems to focus more on fasting than keto, but strongly supports keto diet for his patients, because it lowers insulin and makes it easier to fast.
The IDMP is the world leader in the use of intermittent and extended fasting in the treatment of metabolic diseases. Dr. Jason Fung and Megan Ramos’ clinic in Toronto has successfully treated thousands of clients with fasting for many years. Dr. Jason Fung has lectured physicians throughout the world about this ancient dietary technique, appeared on television, and written a comprehensive bestseller on its use. Other dietary strategies include eating whole unrefined foods, lowering dietary intake of refined grains, added sugars and increasing natural fats.

Thanks, a good article that presents the various fasting methods in simple, easy to read terms. I have been following the 16:8 method for some time now and believe my body and brain are better off as a result. I have also lost some weight although weight loss was not the original goal.

Hi Ron,
I am glad that you found the article useful and thank you for sharing your experience. It really is about finding what works for you.

I’m glad you listed adrenal and thyroid issues as reasons to possibly avoid fasting! I was practicing intermittent fasting by skipping breakfast for close to a year (out of convenience really), but I didn’t listen to my body well and didn’t understand why I didn’t feel great like everyone raves about. When I finally talked to my Functional Medicine doc and he told me I had adrenal issues and should absolutely be eating meals around the clock and having a small snack on hand like nuts and seeds for when I’m on the go and under high stress... it all made sense. Bummer because it was one less meal to buy or fix; but I do feel better now that I’ve realized why it didn’t work for me.

Hi Lauren,
Yes this can be quite common. Many people do try fasting and whilst it can work well for some people, for others it really is not the best tool to use. You really do need to go with what your body is telling you and not just what you are reading. Especially true if you do have adrenal or thyroid issues.