Home FUNDAMENTALS An In-Depth Guide to Water Fasting on the Carnivore Diet

An In-Depth Guide to Water Fasting on the Carnivore Diet

by | Last updated Dec 7, 2021 | FUNDAMENTALS

Fasting has many proven health benefits, from weight loss, healing to anti-aging. If you are on the carnivore diet, doing a long water fast would be much easier than had you been on a high carb diet.

If you plan to do a fast longer than 24 hours, this comprehensive post will answer all potential questions that you might have about water fasting on the carnivore diet.

There is also a 25-page long fasting workbook that you are free to download and start planning your long fast straight away.

This post has turned into a mini e-book, but I would like it to be as comprehensive as possible to help you practice fasting safely and enjoy the many amazing benefits of fasting at no cost.


  1. What happens in your body during a long fast?
  2. What are the health benefits of fasting?
  3. How long should you fast for?
  4. When should you start the fast?
  5. What should you eat before the fast?
  6. What to drink during the fast?
  7. How much fluid do you need a day?
  8. Should you supplement during the fast?
  9. What do you expect to feel during the fast?
  10. How to deal with the first few difficult days of a long fast?
  11. Should you exercise during the fast?
  12. What records should you keep during the fast?
  13. When should you break the fast?
  14. How to break your fast safely?
  15. How often should you fast?
  16. Who should not fast?
  17. Conclusion

Please note that if you have health problems and are currently on medications, it is very important to consult with your doctor before beginning your fast, regardless of its length.

While I try to be as helpful as I can in writing this post, I take absolutely no responsibility for any loss, damages whatsoever arising directly or indirectly out of or in any way related to your use of the information in this post.

What happens in your body during a long fast?

Fasting means not eating, when you are not eating, you are fasting.

When there is no food coming in, your body is relieved of a heavy workload which is digesting food.

After the last few bites of food are digested, your digestive tract can get a complete rest until you decide to eat again.

Now your body has to totally rely on stored energy in the forms of glycogen and fat to function.

The first type of stored energy that your body will turn to is glycogen (long chains of glucose derived from carbs) which is stored mostly in the liver and muscles.

An average adult can store about 2000 to 2400 calories of glycogen.[1, 2]

Depending on your basal metabolic rate and how physically active you are, it generally takes between 12 to 36 hours of fasting for your body to use up the stored glycogen.[3]

Once the glycogen is substantially depleted, your body will start to burn fat for fuel, i.e. breaking down fatty acids and producing ketone bodies for energy. When this happens, your body is said to be in ketosis.[4]

While your body is burning down fat for fuel during a fast, your brain, muscles, and vital organs are spared. From an evolutionary perspective, this makes sense because when you run out of food, you need your brain, vital organs, and muscles to function at the best of their ability to successfully hunt for the next meal.

As your body begins to break down fat to function, it also begins to detox and get rid of environmental toxins which are stored in adipose tissues.[5]

Fasting will also accelerate the autophagy process which is a protective housekeeping mechanism where damaged organelles, misfolded proteins, and invading pathogens are eliminated. This is where many benefits of fasting come from.[6]

However, your fat and nutritional reserves can only allow you to function normally for a certain period of time.

If your fast go on for longer than what your body is capable of, your basal metabolic rate will begin to slow down and you will start losing muscle mass. Without appropriate supplementation, your nutritional status will deteriorate as well which can lead to serious health problems.

What are the health benefits of fasting?

By looking at what happens in your body during a long fast, it is easy to understand why there are so many health benefits associated with fasting.

When food is not coming in, your body is forced to dig into the fat reserve and that leads to fat loss and weight loss. As your fat melts, environmental toxins stored in adipose tissues are also released.

Fasting also deactivates mTOR, a nutrient-sensing pathway, and activates AMP protein kinase which triggers cell repair and inhibits anabolic processes.[7, 8]

In addition, fasting facilitates autophagy where your body goes through the process of cleaning out old and damaged parts of cells and recycling them, resulting in many health benefits.

Animal studies and clinical trials have shown that intermittent fasting increases life span, slows or reverses aging, and improves many health conditions including obesity, diabetes mellitus, cardiovascular disease, cancers, and neurologic disorders.[9, 10, 11]

In the largest observational study so far on periodic fasting which involved 1422 subjects fasting between 5 and 21 days at the Buchinger Wilhelmi fasting clinic in Germany, it was found that the participants experienced significant reductions in weight, abdominal circumference, and blood pressure. Other benefits associated with prolonged fasting were also reported including improvements in various blood markers and reported increases in physical and emotional well-being.[12]

Image showing positive responses of various organ systems to fasting
Responses of various organ systems to fasting. Source: Anton et al (2017)

Although fasting has many benefits, it is not risk free.

In 1978, William Carlton, aged 49, died after 29 days of fasting under supervision at the Shelton Health Clinic. He had ulcerative colitis but other than that was considered healthy. He weighed 192 pounds when he checked into the clinic and died of severe dehydration and malnutrition 29 days later weighing just 130 pounds.[13, 14]

In 2006, Rosaline Gilbert, a devout Christian aged 29, died on the 23rd day of her 40-day fast attempt to emulate Jesus’ 40-day fast in the wilderness. She reportedly fasted regularly and only drank water during her last fast.[15]

How long should you fast for?

Before you start a fast, it’s a good idea to decide how long you are going to fast for because having a clear goal in mind can help keep yourself accountable and better prepare.

Medically supervised prolonged fasts have been done safely lasting from a few days to a few weeks.

The longest supervised fast on record is 382 days. In 1965, Angus Barbier, aged 27 and grossly obese weighing 456 pounds (207 kg) at check-in, began his fast under supervision.[16]

He didn’t plan to fast for that long but because he adapted so well and was eager to reach his ideal weight, he kept going.

By the end of the fast, he had shed 276 pounds (125 kg) and improved many health markers. Five years after the fast, his weight remained around 196 pounds.

Angus Barbier was given daily vitamin supplements during the entire fast and potassium and sodium supplements for parts of the fast. He was allowed to drink non-caloric fluids as much as he liked.

Buchinger Wilhelmi, a fasting clinic based in Germany, has been offering therapeutic fasting programs for over 100 years. Their current fasting programs last from 3 days to 28 days with options to extend.[17]

However, their programs are not strict water fasting. Participants are allowed about 200-250 calories and 25-35 grams of carbohydrates per day from optional honey with herbal teas, fruit or vegetable juice, and vegetable soup. All participants are under the daily supervision of trained medical professionals.[18]

When deciding the appropriate length for your fast, consider the following factors:

1. Your fasting experience

Obviously, the more experience you have with fasting, the longer you can do it safely and with fewer adverse symptoms.

If you have never fasted for more than 24 hours, start with a shorter fast and build it up gradually over time.

For example, if you’ve been eating 3 times a day between morning and dawn, try to eat within a 6-hour window and then do days when you only eat just one meal a day to see how you go.

If you do fine with one meal a day, you can try a longer fast like 36 hours or 48 hours before aiming for a three-day fast or a longer fast.

For your first extended fast, I highly recommend setting a goal that you think you can comfortably achieve rather than a challenging goal just for the sake of it.

If you want to do 5 days, aim for 3 days, you always have the option to extend the fast if you feel well at the end of 3 days and are comfortable doing another day.

And if you are new to the carnivore diet, do wait until you are fully adapted before attempting a long fast.

If you are already fully adapted to the carnivore diet, you will find that a long fast is quite easy to do.

Because your body is already used to burning fat for fuel, you are unlikely to experience many unpleasant symptoms associated with the switch from fuelling on glucose to fuelling on ketone bodies.

I’m on the fifth day of my water fast as I write this post. I set the goal of fasting for 3 days only but still keep going because it’s been relatively smooth so far.

2. The amount of fat reserve and muscle mass you have

The more fat reserve you have, the longer you can fast. As mentioned above, Angus Barbier could fast for 382 days safely because he had a lot of fat to keep going.

If you are very lean with a low body fat percentage, you don’t have much fat to resort to and soon you will begin to lose muscle mass.

According to Dr. Ted Naiman, you can only get about 30 calories per 24 hours out of each pound of body fat.[19]

For example, if you weigh 160 pounds and have 10% body fat, you have only 16 pounds of body fat and can only get 480 calories from your fat storage per 24 hours. If your basal metabolic rate is 1500 calories a day, because you can only get 480 calories from fat, the rest will have to come from your skeletal muscles being broken down.

On the other hand, if you weigh the same but have 32% body fat, you can get 1536 calories from your fat store per 24 hours and you can probably fast for a lot longer.

If you don’t have a lot of fat reserve to sustain a long fast, you have three choices:

  • Stick with intermittent fasting, for example 16/8 or 20/4,
  • Stay with shorter fasts of 24 to 72 hours,
  • Increase your fat intake and bulk up before attempting a long fast, or
  • Trade some temporary muscle loss for the benefits gained from a long fast.

3. Your nutritional status and health conditions

Clearly, the better your nutritional status at the beginning of the fast, the longer you can fast.

If you have a lot of fat reserve but your nutritional status is poor, your risk of health complications from an extended fast increases.

If you have some health problems and are currently on medications, it is definitely not a good idea to attempt a long fast without talking to your doctor first.

When should you start the fast?

Because the first couple of days of a long fast are the hardest, it makes sense to start the fast at the beginning of the weekend or during a period of lighter schedule.

In the first couple of days, you need to get used to not eating at all and will experience transitional symptoms as your body switches from running on glycogen store to running on ketones.

If you are fully fat-adapted and are already in ketosis, you will experience fewer unpleasant symptoms but you still need to deal with hunger pangs at your usual meal times.

If you are working, Friday is a good day to start a long fast. If you eat the last meal before the fast on a Friday, by Monday, the worst would have been over and you can probably go back to work as usual.

If you have a long weekend or long public holidays, start the fast at the beginning of the holidays.

Doing a long fast during the Christmas and New Year holidays is a big challenge but also a great excuse to not indulge in lots of unhealthy food and avoid dealing with unwanted weight gain afterward.

If conditions allow, you could take time off work and totally focus on your long fast.

What should you eat before the fast?

In my view, in the week leading to your long fast, you should focus on nutrient-dense food to boost your nutritional status and eat enough fat to make sure you are already deep in ketosis at the beginning of your fast.

On the carnivore diet, this means eating only ruminant meat and fat and organ meat (e.g. liver, brain, kidney, marrow) and cutting out all dairy, honey or the occasional fruits you might have been having.

A 70:30 fat-to-protein ratio in terms of calories or 1:1 ratio in terms of grams should be sufficient to put you in ketosis on the carnivore diet. However, you can add some more fat to increase this ratio to 80:20 to make sure you are deep in ketosis at the beginning of your fast.

The protocol at the Buchinger Wilhelmi fasting clinic is that on the day before the beginning of the fast, participants would be given a 600 calorie vegetarian diet divided into 3 meals of either rice and vegetables or fruits.

Personally, I think this is a bad idea. Why load up on carbs on the day before you start the fast? Fat should be the emphasis to hit ketosis as soon as possible which can greatly help reduce transitional symptoms.

If you like, you can also ease into the fast by cutting down your food intake slowly in the days leading to the fast. However, I personally find that unnecessary. I would just eat to satiety up to the day before the fast.

What to drink during the fast?

1. Water is the best but tea and coffee are also okay

The best drink during a water fast is the same as during a feasting period: water.

You can also drink other calorie-free drinks like tea, coffee, and herbal teas if you have been drinking those prior to the fast.

Although in my view tea and coffee are not healthy, it might be difficult to fast and deal with fasting symptoms and caffeine withdrawal symptoms at the same time.

However, if you are determined, this is a great opportunity to purge all your bad habits at once: stop drinking tea, coffee, and alcohol and quit smoking as you begin your fast. Your body will be so thankful for that. Many people have found that after a water fast, those addictive substances don’t appeal to them anymore. It does require a lot of willpower though.

For your information, the Buchinger Wilhelmi fasting clinic allows their customers to drink herbal teas with honey (maximum 2-3 teaspoons per day), but no tea or coffee due to their caffeine content.

If you choose to drink tea and coffee, it’s best to keep these drinks calorie-free. But if a little bit of honey, cream or a dash of milk with your drinks can help you stick to a long fast easier, it’s perfectly fine, as long as you don’t overdo it and break your fast.

2. Electrolyte supplement can help with your fast

Electrolytes have no calories and can help you go through a long fast easier. Because they replenish the lost electrolytes, you are less likely to feel dizzy or lightheaded.

In addition, if you are fasting to lose weight, electrolytes can help spread the weight loss throughout the fasting period.

If you don’t take electrolytes, a lot of initial weight loss is due to water being flushed out of your body. Electrolyte supplements help retain water and prevent this massive early weight loss. As a result, you will see a small but steady weight loss throughout the fast instead of a sudden big drop and then a very small weight loss later on.

Electrolytes also help prevent a significant weight regain after the fast due to water retention as your electrolyte intake spikes on refeeding.

However, according to Dr. Jason Fung, a nephrologist and an expert on fasting, you don’t have to take electrolytes during a fast. Your body knows how to maintain an electrolyte balance. If it feels it needs electrolytes, it will recycle through the kidneys. If you feel a bit dizzy during the fast, add a little salt to your drink or under your tongue to help. But if you feel electrolytes help, take them.

When Angus Barbier fasted for 382 days, he was only given potassium tablets for 70 days (day 93 to day 162) and sodium supplements for 11 days (day 345 to day 355).

3. Light bone broth is okay during a long fast

Bone broth contains minerals, collagen, glycine, proline, glutamine, and some electrolytes.

Although bone broth is very nutritious, it can have a lot of calories depending on how long you simmer the bones for and whether you skim the fat off. If your broth has quite a lot of calories, it could break your fast.

I think it’s best to save the bone broth for when you are breaking your fast because when you are not eating anything, bone broth is very tasty and you could end up drinking a lot and are at risk of breaking your fast.

However, if drinking bone broth helps you go through a long fast easier, go for it. A long bone broth fast still offers a lot of benefits compared to no fast at all. So, don’t let perfect be the enemy of good.

The Buchinger Wilhelmi fasting clinic in Germany feeds their fasting clients fruit or vegetable juice for lunch and a vegetable soup for dinner as well as offers optional honey with herbal teas.

Compared to the above menu, I bet that bone broth is much more nutritious. If you want to do a bone broth fast instead of a water fast, try to drink a light broth and keep the total calorie intake as low as possible to accelerate autophagy.

4. Coconut water is an option if it helps your long fast

Coconut water is low in calories and has a small amount of phosphorus, sodium, potassium, calcium and magnesium.

If you enjoy drinking coconut water and if it helps with your fast, it’s okay to drink diluted coconut water but make sure you don’t drink too much that it kicks you out of ketosis and break your fast.

We don’t know exactly how many calories will break a fast, but if more than 20 to 50 grams of carbohydrates a day will kick you out of ketosis, try to stay within the lower bound and consume less than 100 calories a day if you decide to drink any caloric fluids.

A cup of coconut water has between 40 to 45 calories, so if you want to drink coconut water, 2 cups a day is the maximum.

5. Avoid artificial sweeteners during a long fast

I think it’s best to stay away from artificial sweeteners which can stimulate appetite and raise insulin.[20, 21, 22, 23]

A study on mice has found that commonly used artificial sweeteners result in the development of glucose intolerance through the alterations of gut bacteria.[24]

In another study where participants only sipped drinks containing sweeteners and washed out their mouths for 45 seconds and then spat them out again, there was a significant increase in insulin after stimulation with sucrose and saccharin.[25]


In summary, the best drink during a fast is water. However, if other caloric or acaloric drinks like tea, coffee, herbal teas, diluted coconut water or light bone broth help make your fast easier, feel free to include them.

How much fluid do you need a day?

I have previously written in this post on drinks on the carnivore diet that the general rule is to let your body guide you and drink to thirst.

The same should apply during your fast.

If you are a big person, physically active, and out and about in a hot climate, your body will let you know that you need to drink more and vice versa.

The Buchinger Wilhelmi clinic asks fasting participants to maintain fluid intake at 3 liters a day from fruit or vegetable juice (0.25 L), vegetable broth (0.25 L), water, and herbal teas.

I don’t know the scientific reasons for this recommendation but if you like to follow their protocol, go ahead.

Should you supplement during the fast?

Whether you need to supplement with multivitamins during a long fast or not depends upon your nutritional status and the length of your fast.

You can’t know for sure what your nutritional status is like unless you get some tests done.

However, if you have been on the carnivore diet for a while, have no health problems, are generally healthy, and don’t plan to fast for more than a few days, there is some assurance that your nutritional status is good and you don’t need to supplement.

If you have any diagnosed health problems and are taking medications, please check with your doctor to, amongst other things, see if you need to supplement or not.

For your reference, when Angus Barbier fasted for 382 days, he was given daily multivitamin supplements. In addition, he was given potassium tablets (13 mEq daily) for 70 days (day 93 to day 162) and sodium supplements (2.5 grams a day) for 11 days (day 345 to day 355). No other drug treatments were given. [26]

From what I’ve read, the Buchinger Wilhelmi fasting clinic in Germany which has been offering fasting programs lasting from 3 days to 21 days for more than 100 years generally does not give vitamin supplements to their fasting customers.

However, in chronically depleted cases, micronutrients are supplemented and natural essential fatty acids may be given.

What do you expect to feel during the fast?

The types and severity of the symptoms that you might experience during a long fast depend on the kind of diet that you are on before the fast and your health conditions.

In a study involving 1,422 fasting participants at the Buchinger fasting clinic, reported mild symptoms for fasts lasting longer than 4 days were sleep disturbance, fatigue, dry mouth, back pain, hunger, bad breath, headache, muscle pain, abdominal bloating, diarrhea, cold sensitivity, craving, vertigo, blurred vision, restless legs, skin rash, nausea, palpitation, muscular cramp, dizziness, eczema, bleeding gums, etc.[27]

However, most of these symptoms were very uncommon with 2/3 of the symptoms affecting from 0.1% to 3% of the participants and the rest affecting from only 4% to 15% of the participants.

Adverse events like irregular heartbeats, low sodium, hospitalization, low blood glucose, low potassium, gout, vomiting, or abdominal pain were extremely rare, affecting only 1 to 3 participants (less than 0.2%) out of the total 1,422 participants.

Most of these symptoms are “keto flu” symptoms associated with the adaptation process as your body switches from running on glucose to running on ketones.[28]

However, if you have been on the carnivore diet for a while, your body would already be fat-adapted and you will unlikely be suffering from most of those symptoms. I personally find it is so much easier to fast now than when I was on an omnivore diet.

The main symptom you are most likely to get is hunger pangs at your usual meal times for the first couple of days. But this will pass (we will look at some strategies to deal with this problem below).

From an evolutionary perspective, this makes sense because if our ancestors experienced debilitating symptoms after missing a few meals, it would have seriously affected their ability to hunt and survive and threatened their survival.

If you are not on the carnivore diet or the ketogenic diet prior to your long fast, it’s likely that you will go through those symptoms for the first two days of the fast. After that everything will be much easier and you will begin to experience the benefits of a long fast.

Positive things that you can expect from a long fast are weight loss, mental clarity, better skin, initial energy boost, improved blood markers, overall improvements in physical and emotional wellbeing.

Research has shown that the average weight loss is from around 2 lb (0.9 kg) per day for fasts lasting a few days to 0.9 lb (0.4 kg) for fasts lasting longer than 20 days. [29, 30]

The initial weight loss is likely to be higher due to water loss that goes with the drop in sodium if you don’t add sodium to your drinks.

The longer you fast, the smaller the daily weight loss will be because your body will adjust to conserve energy by lowering the basal metabolic rate.

In the Buchinger fasting study, the average weight loss from the 5-day fasting program is 1.4 lb (0.64 kg) per day and from the 20-day fasting program is 0.95 lb (0.43 kg) per day.[31]

In another study, a non-obese subject lost on average 0.96 lb (0.44 kg) per day after 36 days of acaloric fast for religious reasons.[32]

Angus Barbier lost on average 0.72 lb (0.33 kg) per day over his 382-day fast.[33]

How to deal with the first few difficult days of a long fast?

As mentioned above, even if you are new to fasting, you are likely to experience unpleasant symptoms for only the first couple of days of the fast. Therefore, planning the first few days well will increase your chance of success with a fast lasting longer than a few days.

Below are some tips to help make the first few days easier.

You are most likely to experience hunger pangs during the first couple of days at your usual meal times, so please plan ahead what you are going to do at these times of the day.

If you are at work, keep yourself busy at mealtimes by scheduling a meeting, doing some long-term planning, calling your family, going out for a walk, etc.

If there are work functions involving food that you have to attend, plan ahead what you are going to do.

If you are out and about, stay away from food outlets.

If you are home, plan ahead what you’re going to do when other members of your family are cooking and eating. You can go out for a jog, go to the gym, lock yourself into a room and watch your favorite movie, or even watch a video about the health benefits of fasting to help keep you motivated.

If you are the one who has to cook for the rest of your family, cook ahead and freeze enough meals to feed your family for the duration of your fast, plan for somebody else to take over, or organize takeaway.

List down things that you are going to do when you feel hungry during the first couple of days, for example, drink a glass of water or a cup of tea or coffee, go for a walk in the sun, indulge in your hobbies, call your best friend, play a video game, watch some motivational videos, or have a hot bath, etc.

Get enough sleep. This is important during your fast as well as during your feasting period.

Remember to tell yourself that hunger pains will pass and it will definitely get better with time. Most people only experience hunger during the first 2 days. If you are already in ketosis, you are likely to feel hungry only briefly at mealtimes.

If you have been eating a few times a day for all your life, trying to not eat for more than a few days is no small feat. It can be daunting to think about it before starting but if you are already on the carnivore diet, rest assured that it is nowhere as difficult as it sounds.

Should you exercise during the fast?

If your fast only lasts a few days, it should be okay to stick to your regular exercise routine and normal physical activity level.

Exercises can help you sleep better, preserve muscle mass, enhance autophagy, stimulate growth hormone secretion, reduce stress, improve your mood, promote a general feeling of wellbeing, and support weight loss.

If your fast lasts for a lot longer, for example for more than 7 days, and you don’t have a lot of fat reserve, you may want to adjust your exercises and other physical activities according to your energy level. You may consider keeping the normal level of physical movements but reducing the level of intensity or doing both.

If you find that fasting begins to significantly interfere with your daily activities, I think it’s probably the time to break the fast.

Under the Buchinger fasting protocol, at the beginning of the fasting period, participants follow a program of light exercises alternating with rest and individual mild non-physical treatments like hydrotherapy or physiotherapy. Exercises during the fast consist of light to moderate intensity outdoor walks and group gymnastics led by certified trainers.

What records should you keep during the fast?

This is entirely up to you but if you’ve got the time, the more the better.

If this is the first time you fast, it’s a good idea to keep a detailed record of what you drink, the symptoms you experience, how you feel during and after the fast, how you deal with hunger, and any benefits or adverse effects you have.

This will be very helpful in planning your fast next time. Because many of us today live in an environment where food is readily available all the time and I think regular fasting of appropriate lengths should be part of our life.

If you have medical conditions, it’s also a good idea to keep a detailed record of your fasting experience which you can then discuss with your doctor.

Here is a 7-day fasting workbook that can help you plan your fast and keep detailed records of your fast for future reference.

When should you break the fast?

You should break your fast when you begin to experience difficulty performing daily tasks, your hunger return, you feel weak, you feel cold all the time, or when you feel unwell for any reason.

As noted above, fasting is generally safe and most people only experience mild symptoms, but everybody is different.

You may have undiagnosed medical conditions that could be exacerbated by the fast. So, you should stop the fast at any time you feel unwell, you can always try it again later.

All the fasting benefits in the world are not worth it if your fast results in serious and lasting health complications.

How to break your fast safely?

Because your digestive tract has gone through an extended period of resting, it makes sense to reintroduce food gradually.

People who have fasted for a long time can suffer serious health problems if refeeding happens too quickly.

During World War II, many rapidly re-fed prisoners who had been starving for months quickly died after they were liberated and fed again.

Under the Buchinger fasting protocol, the fast-break and refeeding are as follows:[34]

Typically, a ripe apple raw or cooked is eaten slowly. In the evening a potato soup is served.

The ‘refeeding’ diet is a light lacto-vegetarian diet, rich in fiber (whole grain, prunes, possibly linseed) in accordance with individual tolerance, unsaturated fats (cold-pressed vegetable oils), and few saturated fats. Chewing is done slowly and consciously.

On the first refeeding day, approximately 800 calories, on the second approximately 1,000 calories, the third approximately 1,200 calories, and the fourth approximately 1,600 calories are taken up.

Between meals patients should continue to drink plenty of fluids.

The current recommended refeeding regime for patients at risk of refeeding syndromes are as follows:[35]

  • Day 1: 5-10 calories/kg/day
  • Day 2-4: 10-15 calories/kg/day
  • Day 5-7: 20-30 calories/kg/day
  • Day 8-10: 30 calories/kg/day.

In addition, supplements, biochemistry check-ups, and daily monitor are required.

Due to the lack of guidelines on fast-breaking for people who are on the carnivore diet, please talk to your doctor, take it slowly and listen to your body to minimize risks of refeeding syndromes.

Clearly, the longer you fast, the more you need to take it slowly when you break the fast.

This is how I usually break my fast.

On the day I break the fast, I would start sipping light bone broth, a cup every couple of hours. About six hours later, I would have a small steak. The next day, I would eat as normal. However, the longest fast I’ve ever done is only 12 days.

Note that if you haven’t already done it, fast-breaking is a great opportunity to test out food sensitivity.

Start with beef only for a while and then introduce one food at a time. Leave a few days gap in between to observe your body’s reaction to the newly introduced food.

How often should you fast?

The right fasting frequency again depends upon how much fat reserves you have and how good your nutritional status is.

If you have ample fat reserves, if you’ve been eating nutrient-dense food, and if your nutritional status is optimal, you definitely can fast more often.

On the other hand, if you have a low body fat percentage or if your nutritional status is poor, you should not fast too often and not for too long.

Fasting has many health benefits, but fasting too often, your fat, vitamin, and mineral reserves will be depleted.

Fasting also puts stress on your body. While occasional stress can be beneficial, chronic stress becomes harmful.

According to Buchinger clinic, the optimal therapeutic fasting duration is 2 to 4 weeks but individual patients’ initial conditions and their evolution during fasting are always taken into consideration. However, shorter fasting periods are more feasible or medically preferred, especially for underweight people.

Dr. Eva Lischka, former head physician of the Buchinger fasting clinic recommends that:

  • For rheumatic diseases and activated arthrosis, 21 fasting days are recommended
  • For migraines, 14 fasting are recommended. A study shows that 94% of participants who fasted for 14 days had no more or much less migraine
  • Under medical supervision, long fasting periods of several weeks are possible and necessary for good outcomes.

Dr. Francoise Wilhelmi de Toledo, the managing director of the Buchinger fasting clinic says that she used to do a 3-week fast one or twice a year. But now, as she gets older (she’s now 68), she does one 12-day fast a year.

I think it is good to aim for one long fast a year and go as long as you can comfortably can. This would be your body’s “spring cleaning” period. In addition, add in regular intermittent fasting and a shorter fast of a few days once per season.

Who should not fast?

Although fasting has many benefits, there are people who should not fast.

When you are fasting, your body has an opportunity to rest and carry out the necessary repair and maintenance.

But when you are not eating, the essential nutrient supply is also cut off. If that goes on for a long period of time, there can be serious health implications for some people.

The following people should not fast, especially not without clearing it first with their doctor or without appropriate medical supervision during the entire fast:

  • If you are planning to conceive, pregnant or breastfeeding, you should not fast. You need to be in a optimal nutritional status to prepare for the arrival of your child or to nurse your child. Breast milk is the one and the only food your newborn should have. The quality of your milk can affect your child’s health, intelligence and future
  • If you are underweight or have an eating disorder, you should not fast
  • If you are malnourished, you should not fast even if you have a lot of fat reserve
  • If you are under 18, it’s obvious that you should not fast. Your body is going through a growth period, fasting can result in stunted growth
  • If you are an elderly, you should not fast. The Buchinger clinic has clients in their 80s but they would be given a tailored program and under daily supervision of medical professionals the whole time. They would also be given supplements as needed
  • If you are currently ill, you should not fast. There are people who have cured their serious illness with extended fasting but please don’t attempt to do this on your own without consulting with your healthcare providers. If you are malnourished, cutting off nutrient supply may even hinder your body’s ability to recover from illness.

As mentioned above, the best way to find out if you can fast safely for an extended period of time is to consult with your doctor.


Fasting has many health benefits and should become a part of our life today.

One thing for sure is our ancestors would have eaten a lot less and less often than most of us today.

Imagine living with your tribe in the wilderness, you would have to hunt, slaughter the animal, look for water, build shelter, make clothes, and run away from dangers. You wouldn’t have three meals a day plus snacks and it’s likely that you would have to frequently go for days without food.

Today most of us have access to an abundance of calorie-dense food 24/7 while spending most of our time being sedentary in a comfortable environment.

Apart from eating an ancestrally consistent diet and staying physically active most of the time, reducing your feeding window and incorporating a few extended fasts a year can do wonders for your health.

If you find this post helpful, please consider sharing this post and my site with your family, friends, and followers. That would be much appreciated. Please also check out my library of articles on the carnivore diet here which is updated regularly.

DisclaimerThe information in this post is for reference purposes only and not intended to constitute or replace professional medical advice. Please consult a qualified medical professional before making any changes to your diet or lifestyle.

Photo creditGiorgio Trovato on Unsplash