Extended Fasting [How To Use With Keto]

  • Author: Kara
  • Date: May 8, 2023
  • Time to Read: 8 min.

Extended fasting is a form of intermittent fasting. It brings with it no end of health benefits and can produce some amazing results when combined with a keto diet. In this article, we will take you through what extended fasting is the health benefits, some things to be aware of, as well as how to get started with extended fasting. Be sure to read until the end when I will take you through my personal experience with extended fasting, including top tips on how to make it work for you.

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What Is Extended Fasting?

Extended fasting is a form of intermittent fasting. When extended fasting, people will refrain from eating for a period of 36 up to 72 hours.

The human body is capable of fasting for over 72 hours, but generally, this is not advised without medical supervision.

Check out our beginner’s guide to fasting on keto.

Extended Fasting on Keto

During the fasting period, no food will be consumed and only water and non-caloric beverages, including electrolytes, can be consumed.

What Does Extended Fasting Do To The Body?

The main impact extended fasting has on the body is that it alters your metabolism to burning fat as its fuel source, as opposed to sugars (carbohydrates).

This metabolic change is the same as what your body undergoes when you transition into ketosis when you eat a keto diet.

Extended fasting will mean that your body will burn through its glucose (sugar) stores, once these stores are depleted, the body will look for an alternative source. The next fuel source that the body will look to use is fat.

There are many abbreviations that are used in the keto world. Check out our guide to keto terms and guide to keto abbreviations to help you on your keto journey.

However, there are even more abbreviations that are associated with fasting. If fasting is something that you are interested in, it may be worth reading and printing out our intermittent fasting glossary of terms.

Let’s get into the benefits of extended fasting, so you can explore whether this is something for you.

What Are The Benefits of Extended Fasting?

There are a whole host of benefits of extended fasting. Below we have outlined some of the main ones for you.

Fat Loss

As your body transitions to using fat for fuel (known as becoming fat adapted), your body will be burning through your fat supplies. This reduces the amount of fat in the body and can be measured by tracking your fat percentage.

Muscle Definition

This links in with fat loss above. The more fat you lose from around your muscles, the more you will see the definition of your muscles. This is why extended fasting is often used by bodybuilders, before a competition.

Rebuild Your Immune System

Extended fasting for 72 hours has been shown to have a significant impact on the immune system. It encourages the repair and renewal of cells that support the immune system.

Deeper Ketosis

Ketosis is when your body uses fat for energy instead of glucose. Entering into ketosis is what everybody eating a keto diet is seeking to achieve. Deeper ketosis brings with it its own list of health benefits, allowing the body to repair and regrow.

Increased Autophagy

Autophagy is a process where cells degrade themselves through lysosomes. This process helps the cell recycle damaged proteins and organelles. The process of autophagy is essential for cellular homeostasis and survival.

Reducing Inflammation

Fasting helps reduce inflammation because it causes the body to release hormones such as glucagon, which reduces blood sugar levels. This leads to lower insulin levels, which decreases inflammation.

Resets Gut Microbiome

By fasting for 24 hours, or longer, our bodies begin to detoxify and cleanse themselves from toxins. When our gut microbiome is in balance, our guts will help us digest food easier, leading to less bloating and discomfort.

Improved Blood Pressure

Intermittent fasting has been shown to improve a number of metabolic markers in the body, blood pressure being one of these.

Mental Clarity

After your body cleanses itself of toxins, your mind has access to a cleaner bloodstream, which results in clearer thoughts, faster processing, better memory, and sharper senses as a whole.

Hormonal Balance

Extended fasting gives the body the time it needs to reset its hormonal balance. This can help with a whole host of issues such as mood, and skin condition.

Insulin and Leptin Rebalance

As with hormones above, the ‘rest’ that extended fasting gives your body allows your body time to reset its insulin and leptin levels.

Weigh Loss

It is unsurprising that one of the outcomes of extended fasting for a period of time will lead to weight loss.

A study completed in 2019 concluded that people who underwent several periods of fasting over a year period lost significantly more weight than those that did not.

What are The Health Risks With Extended Fasting?

There are no specific health risks associated with extended fasting (36-72 hours) for fit and healthy people. If you are on any medications or have any particular health concerns, you should consult with a health care provider before undertaking extended fasting. 

However, some side effects that you may experience are;

  • Hunger  – a surprise, I know, this should subside after the first 24 hours
  • Fatigue – this is likely to occur when your body has exhausted all of its glucose stores and is looking for more, when it can’t find any, it will be ‘out of fuel’. This fatigue will soon subside when the body goes to its backup plan of finding fat to use as fuel.
  • Trouble Sleeping – this is a common side effect of keto. Your body is undergoing a lot of metabolic changes, this can briefly cause sleeplessness.

Have you tried extended fasting with keto? Have you experienced any other side effects, if you have, let us know in the comments below.

Who Should Try Extended Fasting?

A lot of people will ask me whether they should try extended fasting. This is not really a question that anybody can answer for somebody else. This will really depend on your mindset and what you have done to prepare for extended fasting.

There is no hard science as to who should try extended fasting, however, for me, if you are new to keto, going jumping to extended fasting could be a lot for your body to handle in one go.

Step By Step Guide To Getting Started With Extended Fasting On Keto

I would suggest that extended fasting on keto is for those people who have been through the following steps;

SETP 1: Got to grips with keto

STEP 2: Is fat-adapted

STEP 3: Is accustomed to intermittent fasting 

STEP 4: Has successfully completed a couple of weeks at 20:4

STEP 5: Has completed a few rounds on OMAD

STEP 6: Has successfully completed ADF.

It is only at this point that I would recommend that somebody attempt extended fasting.

What Can I Eat During Extended Fasting?

The answer to this is a simple one, nothing!

If you are completing extended fasting, you cannot eat anything during your fasting period.

Ensure that prior to and post fasting that you eat a nutritious meal that ensures that you hit your keto macros. Check out our guide to getting started with intermittent fasting for how to prepare, prior to going on a fast.

Our guide to breaking a fast will take you through how to safely come out of a fasting period, without undoing all of your hard work.

What Can I Drink During Extended Fasting?

This is another common question that I get asked.

Check out our guide for further information as to what you can drink during your fast. But basically, water, black coffee, and green tea are all great options that are not going to break your fast whilst EF. 

Staying hydrated whilst fasting is essential.

How To Get Into Extended Fasting?

As we have discussed above, it is not advised to suddenly jump into extended fasting. It is advised that you first become familiar with intermittent fasting, eating one meal a day (OMAD), and alternate-day fasting (ADF) before attempting extended fasting. 

Once you have been successful with all of the above, begin with a 36-hour fast and then build up from there to completing a 72-hour fast.

How Long Should I Fast For?

Studies have shown that the most benefits from fasting are gained between 36 and 46 hours. 

As discussed above, any fasting over 72 hours should be supervised by a medical professional.

Start out with a 36 hours fast and see how that goes for you, and you can build for there.

Extended Fasting [My Experience]

The first fast I ever completed was supposed to be a 36 hour fast.

SPOILER ALERT: I didn’t make it!!

This wasn’t surprising. I’d not prepared in any way for the fast, I’d just decided it was something that I was going to do.

I’d not had a nutritious meal prior to starting the fast, I didn’t keep hydrated, or none of the tips we’d recommend here.

How long did I last?

I lasted a whole 18 hours – and for 8 hours of this, I was asleep!

Please don’t let my experience but you off trying intermittent fasting, learn from my mistakes.

We’ll take you through our top tips below.

Top Tips for Extended Fasting Sucess [Tried and Tested]

Here are our top tips for extended fasting success;

  1. Ensure that you are well hydrated before and during your fast
  2. Eat a healthy nutritious meal before you begin your fast
  3. Do not suddenly start exercising during your fast if you wouldn’t have normally
  4. If you are used to exercising, try and work at 70% capacity
  5. Plan your meals for after your fast so you do not undo all of your excellent work
  6. You know your own body, if something doesn’t feel right, stop and seek medical guidance

Breaking Your Fast

What Do I Eat When I Break A Fast?

So as not to undo all of the hard work and health benefits of your fast, plan your exit strategy before you even begin your fast.

After not eating for as long as 72 hours, you will need to ‘warm up’ your gut before returning to eating solid foods. For keto eaters, we would recommend a mug of bone broth, to begin with.

Then eat a small meal designed NOT to upset your digestive system.

Check out our article on what to eat to break a fast for the ultimate guide on this.

What Time Should I Break A Fast At?

It is advised that you break a fast in the late afternoon or early evening. This way, you will not have long to wait for your last meal on your last day of fasting. More importantly, you will not be waking up your gut and then going straight to bed.

Doing so may result in a restless sleep.

Can I do Extended Fasting If I have a Medical Condition?

If you are already on medication or have any diagnosed, or undiagnosed health conditions, please do not undertake a fast.

Consult with a medical professional, or registered healthcare provider before undertaking intermittent fasting on keto, or even if you are not combining intermittent fasting with keto.

Intermittent fasting is not particularly not advised for those with amenia.

How Often Should I Do Extended Fasting?

It is only advised that you should do an extended fast 3-4 times a year maximum. This way you will get all of the health benefits, without putting your body under too much stress.

Final Thoughts: Extended Fasting On Keto

Yes, extended fasting is hard, however, it can be combined with the keto diet for some phenomenal results. You don’t have to jump string into extended fasting though, start with regular intermittent fasting and build up from there.

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