Alternate Day Fasting [ULTIMATE Keto Guide]

  • Author: Katie
  • Date: October 9, 2022
  • Time to Read: 9 min.

Alternate day fasting has become increasingly popular, regardless of the diet they are on. Only recently have people been combining it with the keto diet and seeing the shocking effects. In this article, we will take you through what alternate day fasting is, the pros and cons, as well as how to effectively combine it with the keto diet. Don’t miss out on our top tips at the end.

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So, What Is Alternate Day Fasting?

Before we get into the pros and cons, I guess we should go through the basics of alternate day fasting, and how this can be combined with the keto diet. 

Alternate day fasting comes under the broader heading of ‘intermittent fasting’. It is one of the different takes on this concept.

For more information on fasting check out our guide to intermittent fasting on keto.

It involves fasting for a period of 36 hours, followed by a feeding window of 8 hours.

Some people interpret ADF as not eating on one day and then eating on the next. We would advocate the 36 hours due to the health benefits that the body starts to see at 36 hours.

Alternate Day Fasting Keto

See our guide to the keto fasting timeline to understand more about the health benefits which are triggered at different points on the fasting timeline.

A ‘feeding window’, also known as a ‘refeed period’, is the period in which you are allowed to eat. It is in this period that you ‘refeed’ your body with the fuel that it needs.

There are a lot of terminologies which is associated with intermittent fasting. Where possible, we will try and remember to explain the terms, but in case we forget, we’ve pulled together an intermittent fasting keto terms guide for you. Feel free to print it out or bookmark it.

If intermittent fasting is something that you are considering, it may be useful to have with you.

We also have a guide on keto terms and keto abbreviations, these may also help you on your journey.

What Does ADF Do To The Body?

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

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

ADF will mean that your body will burn through its glucose stores.  Once these glucose/sugar/carbohydrates stores are depleted, the body will look for an alternative fuel source.

The next fuel source that the body will look to use is fat as fuel.

Now we understand the basics let’s get into the benefits of ADF, so you can explore whether this is something that you would like to try.

What Are The Benefits of Alternate Day Fasting?

There are a number of benefits to ADF we have pulled together some of the main ones for you below.

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.

Deeper Ketosis

Ketosis is when your body uses fat for energy instead of glucose. Entering into ketosis is what everybody eating a keto diet seeks 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, and rebuild.

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 of toxins. When our gut microbiome is in balance, our guts will help us digest food easier, leading to less bloating and discomfort.

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

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

Appetite Management

Extended fasting has actually been shown to assist in reducing an individual’s appetite in the long term. This can be great for people who have been overeating for a long time and need an opportunity to reset this balance.

As you can see that are a lot of non-scale victories (NSVs) which are associated with extended fasting. The benefits of these are often far greater than any weight loss you may see.

Weigh Loss

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

ADF and keto, can show particularly good results in people who are classified as morbidly obese.

These quick wins can be motivating for people who have struggled with their weight for a long time and can prove the concept that ADF works, and will encourage them to keep going with their weight loss journey in order to meet their health goals.

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 Cons of ADF?

As with anything that has pros (especially as many as ADF), there are going to be some cons associated with it. We have listed some of these below for you.

Some side effects that you may experience doing ADF are;

  • Hunger  – a surprise, I know, this should subside after the first 24 hours. It will improve every time that you do ADF, assuming you are fueling your body right in between, we will go through this below.
  • 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. If you are already eating a keto or low-carb diet, the impact of this is likely to be less.
  • Trouble Sleeping – this is a common side effect of keto. Your body is undergoing a lot of metabolic changes, which can briefly cause sleeplessness. It is only brief, and if you are combining ADF with keto, this is not a side effect that you should be concerned about.

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

What Can I Eat When Doing Alternate Day Fasting On Keto?

The answer to this is a simple one, nothing!

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

Ensure that prior to and post fasting that you eat a nutritious, healthy meal, ideally high in fat, low in carbs, and moderate in protein.

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,  including what to eat and when without undoing all of your hard work.

What To Eat During Your Feeding Window

As discussed above, you should aim to eat nutrient-rich foods during this period. 

As we discuss in our guide to breaking your fast. Your first meal should be something small in order to wake up your digestive system.

After this, you should try and eat two further meals over your feeding window. These should be designed to ensure that you hit your keto macros.

What Can I Drink When Doing Alternate Day Fasting And Keto?

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 AFD. 

Staying hydrated whilst fasting is essential. This includes ensuring that you keep your electrolyte levels up.

Will I Be Able To Do ADF?

A lot of people will ask me whether they should try ADF, or who ADF is for.

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 ADF, or somebodies commitment to improving their health.

To go from overeating, to suddenly not eating for prolonged periods can be a big step.

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

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

SETP 1: Got to grips with keto (if you’re just getting started, check out our keto beginners guide)

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

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

You are also likely to get your best results at this point as your body will already be used to burning fat as fuel.

How Often Can I Do Alternate Day Fasting?

ADF can be done for a week, or longer at a time. There have been reports of ADF being adopted as a lifestyle, which people doing it for months.

I have only ever done this for 8 days (four fasting, four feeding).

If you are going to do this for any prolonged period, please seek medical advice first.

Top Tips for ADF Sucess [Tried and Tested]

Here are my top tips for ADF;

  • Have a good nutritious, healthy meal beforehand
  • Plan your activities. I like to fast when I know I’m going to be really busy in my life, so I am not focused on my food. Equally, I will not try to do this if I know I’m going to have a physically excessively strenuous day
  • Only do gentle exercise over your fasting period
  • Drink plenty of water
  • Plan what you are going to eat to break your fast, this will not only ensure that it is a nutritious meal, but also that it is something that you are going to be looking forward to.

Are you an ADF? Do you have any top tips you can share with the community? If so, please share with us all in the comments below.

Can I do ADF If I have a Medical Condition?

ADF can be beneficial for a number of medical conditions, but if you are taking any medications or have health conditions, please seek medical advice before beginning an ADF.

Can You Exercise When Doing ADF?

Everybody will be different. I would suggest that for your first go at ADF that you do not try and do any strenuous exercise.

After this time, you will have a benchmark to be able to assess for yourself what you think your body is capable of.

What is Modified ADF?

Modified alternate day fasting, takes on the principles of Fast 500 and will see people fasting one day, and then eating 500 calories the next day. Again, these 500 calories should be split to;

  • 70% Fat
  • 25% Protein
  • 5% Carbohydrates

Check out our article on the Fast 500 and keto for more information on this.

I’ve Mastered ADF What’s Next?

If you have mastered ADF and keto, well done!! I know when I first attempted it, I found it particularly difficult.

When you get into it though, the benefits make you even more determined to succeed at it. For those who have mastered ADF, the next step you may want to consider is extended fasting.

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

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

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

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