What happens when you fast for five days?

(NOTE: I’m making some minor updates to this article as we promote the launch of the upcoming Fasting Program, titled Fasting 3.0. Although this article pertains to multiple days of fasting, most of our students stick to fasting for around 16 hours daily and some may experiment with longer multiple-day fasts.)

The truth is that I don’t know what happens to you…but… I’m just wrapping up five days of fasting and want to share my experience so that you understand why you would fast, as what you might expect.

First you might be asking yourself:


Why should / would you fast?

Good question. Many people fast for different reasons. Some fast for religious reasons while others fast for health reasons. Here we’ll focus on the health reasons for fasting. Here are just a few of the benefits:


Weight management. When fasting, it’s generally easy to lose weight…obviously because you aren’t eating anything!

Maintain or build muscle. Losing weight while fasting seems obvious. But what’s less obvious that many people don’t know is that you can fast to maintain and build muscle. There’s a common conception that your body will burn its own muscle when fasting. Your body actually conserves muscle while fasting and boosts production of human growth hormone – which helps promote building muscle.

Lower inflammation. You dampen inflammation, slow down the aging process, and optimize biological function.

Improve brain health and cognition. Fasting promotes the growth of new brain cells, reduces oxidative stress and reduces neuronal dysfunction that results from Alzheimer’s, Parkinson’s and other similar diseases.

Slow and reverse markers of aging.  Because aging is commonly defined as the accumulation of dysfunctinal proteins and organelles in our cells, and fasting reverses this process by stimulating cells to “clean house”, you are essentially slowing down and reversing aging when fasting.

Prevent chronic diseases. Like cancer, diabetes, heart disease, alzheimer’s, and so on. Fasting has been shown to delay the growth of tumors. Fasting improves insulin sensitivity which can prevent diabetes.


Now that you’ve seen some of the benefits of fasting, let’s answer the following question:


What can you expect to happen when you’re fasting?

Remember that everyone is different and this is simply my current understanding of fasting based on the research I’ve done.

And remember too, that fasting is a stress on your body and the benefits you gain are your body’s reaction to this stress. Thus it doesn’t mean that more fasting is better. In fact, you can do more harm than good – especially if you already have some health issues.

You’ll generally experience some of these things simply by fasting for more than 12 hours overnight, mainly while sleeping. However, these processes generally increase as you go longer and longer without food.

Your insulin drops. Fasting increases insulin sensitivity which generally improves energy production and fat storage.

Your glycogen is depleted. Your glycogen stores last about 24 hours and once depleted you may feel shaky, nervous, sweaty, even constricting chest pain and confusion.

You create glucose / Gluconeogenesis. 1-2 days into your fast, your liver manufactures new glucose from amino acids (from proteins) in a process called gluconeogenesis, which literally means “making new glucose”.

You clean up your cells / Autophagy. This cleanup peaks 2-3 days into your fast. It’s essentially your body’s way to clean up your old and dying cells and make way for new ones.

You burn fat for fuel / Ketosis. You reach your peak level of fat burning 2-3 days into your fast when your body uses fatty acids and ketones for energy. After four days of fasting about 75% of the energy used by your brain is provided by ketones.

You conserve proteins. About 5 days into your fast you will be producing high levels of human growth hormone to maintain muscle mass and lean tissues. You’re also producing more adrenaline to prevent a decrease in your metabolic rate.

This chart simplifies the timeline of these processes:

Fasting Timeline


Now you have a general idea of what happens when you fast. So now you must be wondering:


What can you expect based on one person’s experience from a five days fast?

Now it’s time to share with you my fasting journey so that you can hopefully learn what might or might not work for you when you take your own journey…


What’s my back story?

Bulletproof Diet for 3 years. I’ve been following the Bulletproof Diet to some extent for the past three years. What’s the Bulletproof Diet? It’s essentially a Low Carb Healthy Fat (LCHF) / Ketogenic (Keto) diet that consists of lots of healthy fats, moderate proteins and limited carbohydrates. It’s often known for Bulletproof Coffee which is high quality coffee blended with grass fed butter and MCT oil. It’s worth noting that I often overdo it on the carbs – particularly sweet potatoes and white rice – eating carbs on most days.

Intermittent Fasting (IF) for 2 years. I’ve been doing some form of IF for about two years or so in which I either fast for 12-16 hours every night or I fast 12-16 hours and have some form of Bulletproof Coffee / Tea / Bone Broth in the morning – to get fats and MCT oils to get my brain going.

24 hours fasting about 2 times per month. I started doing about 24 hours of fasting on a regular basis early in 2017 (as part of Ben Greenfield and Dr Daniel Pompa’s “True Cellular Detox” program) and have continued doing that up until my 5 day fast.

4 days fast April 2017. This is the longest fast that I had done until now. I drove from Denver to Los Angeles and drank just one decaf Bulletproof Coffee and then drank only mineral water for the next three days. I felt tired, sluggish, weak and cold after the first day of the fast. I ended up breaking the fast just after four days with some nuts and berries which upset my stomach. Unfortunately I didn’t experience that burst of energy that many people report.


What happened during my 5 day fast? 


The 60 Hour Keto Reboot. A friend of mine who sells exogenous ketone supplements happened to be doing this keto reboot that coincided with the kick-off of my fast. At first I thought it wasn’t a good idea but then decided that it may be a good way to “hack” my fast by making it both easier and more effective. Essentially they give a protocol of taking their various exogenous ketone supplements for 2+ days.


Fasting Day 0

I started my fast on Sunday night and that day I now remember eating bread, chocolate, ice cream, cheese, milk, and a few other things that may or may not have supported my upcoming fast. My excuse was that I would be “cheating” and supplementing with exogenous ketones that might make the fast much easier, so why not indulge? I started my fast at about 8pm with the Keto Kalm supplement w/ Beta Hydroxybutyrate, Erythritol, Natural Flavor, Cocoa Powder, HICA, Rooibos Extract, 5-HTP, L-Theanine, Stevia, Xantham Gum, ac-11, Zinc Gluconate.


Fasting Day 1

How did I feel?

Hungry! I definitely felt the urges to eat real food.

However, I was supplementing with ketones, bone broth and a few other vitamins and minerals which took my energy levels, focus, and clarity to an unexpected high.

For example…

I did a short (neuro-mass) bodyweight workout of push ups, pull ups, squats, abs, and short bridges. It was MUCH easier than usual so I did extra reps and holds.

I also did my first initial ice breaker speech at Toastmasters. Although the speech didn’t go so well – mostly because I didn’t prepare well – I felt great. My anxiety was very low and I was in an unusually social, upbeat mood. This may be partly due to supplementing with piracetam just before going to the toastmasters event.


What did I consume?

Keto Reboot

  1. Keto OS Max (w/ caffeine): Beta Hydroxybutyrate, Erythritol, L-Taurine, Fermented L-Leucine, Citric Acid, Natural Flavor, Vegetable Juice Color, Stevia, Xantham Gum, Caffeine, Beta Carotene
  2. Decaf Coffee w/ Chaga and Reishi Mushrooms
  3. Signal OS: Vitamin B12, ac-11 (Inner Bark of Uncaria Tomentosa), Eleutherococcus senticosus, Reishi mushroom, BioPirene (Black Pepper Extract)
  4. Broth Ketones: Natural Beef Broth, Natural Flavor, Natural Chicken Broth, Beta Hydroxybutyrate, L-Leucine (Fermented), Type II Collagen Peptides, Xantham Gum, ac-11, Hyaluronic Acid, Potassium Citrate.
  5. Keto OS Max (no caffeine)
  6. Broth Ketones
  7. Keto Kalm
  8. Signal OS
  9. Water w/ Himalayan Sea Salt


Fasting Day 2

How did I feel?

I felt good. I got some good movement and exercise in. I got a good amount of work done.

But then I hit a wall at about 8pm. Even with all the supplements, I was tired, cold and ended up going to bed early.


What did I consume?

keto reboot ingredients

Same Keto OS Reboot protocol as yesterday.


Fasting Day 3

How did I feel?

After hitting a wall at the end of day 2, I eventually started feeling better. My sleep was better than normal – although I was still supplementing on day 2 so I imagine that may have helped.

I was feeling tired and lethargic. I canceled a phone meeting and took a nap! Not something I usually would do. But then I felt better  – with a bit more energy – in the evening.


What did I consume?

Water with himalayan sea salt. Much easier to track!


Fasting Day 4

How did I feel?

I definitely felt better with more energy in the morning. I got outside in the 60 degree weather and my body seemed to adjust via thermogenesis which is a good sign because I was cold before.

I thought maybe I “turned the corner” and would have this burst of energy that some people report. Although I did have more energy than day 3, I was a bit weaker and more lethargic than usual.

In the evening I got very cold. Usually temps of about 65 are fine for me. However, I turned up the heat past 70 and was still cold.


What did I consume?

Black decaf coffee
Water w/ himalayan sea salt


Fasting Day 5

How did I feel?

I guess that I felt about the same as I did on day 4. Perhaps just a little less energy. I tried jogging a bit and could tell my body wasn’t into it.

One challenge was knowing that I was going to start breaking my fast in the evening so I was definitely thinking about that bone broth!


What did I consume?

Black decaf coffee
Water w/ himalayan sea salt
I began to break my fast with bone broth with himalayan sea and ghee at about 6:30 pm


Fasting Day 6?!

How do I feel?

Today I feel okay. I’m tired; feeling like I didn’t get enough sleep last night. But I’m still working my way through and decided I won’t take a nap.


What do I consume?

Water w/ himalayan sea salt and lemon juice

Decaf Coffee with Ghee and Brain Octane

I officially broke my fast just before 11am… salmon w/ olive oil, lemon juice, cheese and cayenne. It was delicious! And it was about the only food I had in the house so that’s why I decided to eat it.

In the afternoon I ate sardines in olive oil with avocado, whey protein and creatine. It was really good but I did notice it upset my stomach a little bit. My guess is that it was the sardines because they almost always do seem to cause some kind of reaction – yet for some reason I still eat them!


How did I sleep?

Overall, my sleep didn’t seem much better or worse than usual – especially in terms of my sleep tracker, the Oura ring. My best sleep score was between days 2 and 3; while my worst sleep score was between days 5 and 6.

I did, however, have some crazy dreams – especially dreams about food! On Thursday night my tracker didn’t even work for the first few hours of sleep most likely because I was so cold.

I also seemed to be waking up earlier than usual; or, at least, my body seemed to wake up earlier than usual. I guess that makes sense because I was going to bed slightly earlier and I wasn’t eating any food which I imagine changes my circadian rhythms.


Was I in ketosis?

According to the pee strips, I was not in ketosis on Sunday night (day 0). However, I was in ketosis Monday morning and have been since. (Technically speaking, I’ve been peeing ketones.) This is the longest and deepest I’ve been in ketosis so I’m hoping to keep it going with a mostly keto diet going forward. But…

I’m going to Hawaii on vacation in just two days – so it will be challenging!


What’s my conclusion?

The biggest takeaway is that I felt unusually energetic, strong and happy on day when was I was taking the ketones – while I assume still having some glycogen as fuel as well. So it seems this combination of carbs and ketones may be a recipe for big energy spikes.

I’m wondering if there are additional benefits to the keto reboot I did in terms of speeding up autophagy and ketosis. Obviously I felt great on day one but I’m wondering if the ketones accelerated it. And did the ketones help spare any potential muscle loss?

Anyway… I think this was more successful than my four day fast because I feel like I did turn a corner and get some energy back whereas when I did the four day fast I was even more lethargic.


What do you think?

What’s been your experience with fasting?

What do you think about mine?

Post a comment and let me know!

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About the Author Jason Ryer

Helping people cut through the B.S. to finally lose weight, keep it off and beyond for: fat loss, energy, strength and immunity... to reach their (super) human potential!

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