What’s it like to fast for 5 days?

There is a lot of buzz on the Internet about fasting these days.  When I tune into my favorite podcasts, such as Tim Ferriss, Peter Attia, or Robb Wolf, there is always someone talking about fasting.  And that is not a bad thing!  Just look at Dr Jason Fung’s website, where he is helping thousands of people lose hundreds of pounds in the cheapest of all possible ways–by not eating! 

Although the concept of a fast has been understood for millennia, I would forgive you if you have gotten confused lately with the variety of different fasting approaches that are out there.  From the fasting mimicking diet (FMD), to intermittent fasting (IF), to nonsense things like juice fasts, there are a plethora of eating strategies that have been dubbed “fasting.”  But let’s be clear: there is really only one type of fasting and that is where you do not eat anything for period of time. 

Why should you fast?

We’ve written extensively about fasting here and here and here.  I fast because it improves my metabolic flexibility, resets my cravings for food, improves body composition, improves weight and blood pressure, and quite simply it’s a worthy challenge both physically and mentally!  In short, fasting is an exceptional tool for metabolic health and self-mastery.  Although I practice regular IF, prolonged fasting (>36 hrs) is another tool in the arsenal with different benefits.  Unlike IF, which primarily seems to help metabolic issues, longer fasts (3 to 5 days+) are thought to contribute and longevity and cancer prevention through cellular autophagy—literally when your body “eats itself” to get rid of weak, flawed, and even cancerous tissues. 

Who should fast?

Cue the warning disclaimers.  It goes without saying that fasting, especially for more than a day, is a potentially dangerous activity, albeit one with great potential.  If you are seriously thinking about trying a long fast you need to clear it with your doctor first.  This is especially true if you are taking any medications whatsoever.  Pregnant women, nursing mothers, and children should never attempt this under any circumstances.  There is increased interest in the use of fasting for patients with cancer receiving chemotherapy and radiation therapy.  The jury is still out on whether this is beneficial or not, but recent studies show that fasting for a few days prior to chemotherapy significantly reduces the toxicity associated with the drugs and may even increase the efficacy.  In a separate study, albeit in rodents, researchers showed that fasting prevented death from what would be an otherwise lethal dose of radiation.  This has led to increased excitement around the applications of fasting in oncology, but the jury is still out.  Although this is exciting new, if you or a loved one is facing cancer and interested in the therapeutic power of fasting, you must discuss this with your oncologist first and make sure you are monitored closely throughout.

How to structure a 5-day fast?

In my opinion the best way to structure this is during the work week.  There is no doubt the fasting is easier when you are busy.  You simply have less time to think about eating and preparing meals.  In today’s office environment, it is also acceptable to work through lunch and skip breakfast.  Dinnertime with the family is still a challenge, but it is easier on those hectic weeknights than it would be over a weekend or during a vacation.

If you decide to fast during the work week the most logical way to do it would be to eat your last meal on Sunday night and the clock starts at that point.  Your next meal can take place at that same time on Friday night. 

Day 1

For many people, the first day of the fast can be the hardest.  But if you practice regular fasts of 24-36 hours, the first day is really no different than a typical Monday.  Except that you do not get to eat that night.  Or the next night.  Or the night after that…OK its starting to sound daunting, right?

There is no doubt that fasting is much easier if you are already fat adapted, or eating a ketogenic diet.  I have found that the transition to fasting is a lot easier if I do not have a big “cheat meal” the night before and stay ketogenic instead.   

As if cutting out all food wasn’t hard enough, if you’re doing a true water only fast, the coffee has to go as well.  For me, this is the toughest part of the first day.  When I do a typical 24-hour fast I usually have black coffee—sometimes a few times during the day.  But on a longer fast where the intention is to break habits, cravings, and get a deep cleanse, I think it is useful to eliminate coffee/caffeine as well.  Adding an extra layer of caffeine withdrawal on top of the food cravings can make you one hangry beast, so watch out!  However, if the thought of dealing with caffeine withdrawal headaches has you feeling defeated, planning to drink one small cup of black coffee or green tea during a fast is not the worst thing in the world.  After all, caffeine is a stimulant, and stimulants will suppress your appetite.  Just be careful not to overdo it.

Day 2

As you enter day 2, the first thing you might think about it is the way that fasting affects your sleep.  I have found that it affects different people in different ways.  I tend to sleep really well on the first night of a long fast, then it usually deteriorates as the week goes on.  Sometimes I find myself laying in bed wide awake, ketones rising and energy raging.  Other times, I have developed muscle cramps (more on that below).  Bottom line is that sleep can be challenging when fasting.   

Another factor to consider early in a prolonged fast is your sodium/electrolyte intake.  When we switch to a ketogenic metabolic state, the body undergoes a diuresis, ridding itself of excess fluid and electrolytes.  After a few days, the deficit can become pretty significant.  The first way this electrolyte deficit becomes apparent is that you feel low energy, muscle aches/cramps, and other symptoms of the “keto flu.”  I found this out the hard way on the first long fast I did, when I woke up in the middle of the night with severe leg cramps that only relented after a warm Epson salt bath. 

It is important to replete your electrolytes when fasting, including sodium calcium and magnesium.  In my most recent fast, I used the perfect keto electrolyte supplement and it was a complete game changer, with virtually no keto flu symptoms.  In the past I tried to replace my electrolytes by using things like smart water, but since the electrolytes make up a minority component, I think all that water drinking just further dilutes your electrolytes. And although potassium is quite important, I do not recommend supplementing with it as over-repletion can cause serious issues like cardiac arrhythmia.

Day 3

Is anyone else feeling cold?  Typically by this point in the fast, your metabolic rate really starts to slow down and this has a couple of effects, most notably the constant sensation of having a chill.  We have done fasts in the summer and by the midway point were attempted to turn off the air conditioner.  I am a very warm natured person so this was a very weird experience for me.  We found its particularly noticeable at night, but this is an easy one to solve, just drink some hot water or cover up!

In an earlier post, we talked about the possibility of working out in the fasted state and the benefits that can be garnered.  However, realize that fasting for days on end is a completely different ballgame than intermittent fasting.  Nevertheless, we’ve done an intense spin classes 48 hours into a fast and felt fine during and afterwards.  On my most recent fast, I lifted reasonably heavy and likewise felt fine.  One concern to keep in mind is that when exercising we will invariably sweat and therefore lose more electrolytes.  You need to keep close tabs on this and make sure you are repleting them appropriately.

Day 4

Hunger.  Can you believe it took until day 4 before I even mention this?  If you try a long fast, you might be surprised that what you thought would be the hardest part is not really that big a deal at all.  This is not to say that you will not feel occasional hunger pains or dream about food—that’s inevitable.  The incredible thing is how easy it is to conquer those cravings/signals that you have always honored in the past.  By day 2 you realize that hunger is mostly in your head.  It is a powerful stimulus, but your willpower is more powerful…trust me.  When doing a fast, I struggled more with what to do during mealtimes which are firmly embedded in our culture and habits.  When you are not eating or preparing food you realize how much free time you have, and invariably you start to think about food.  Another curious fact is that most people think the hunger pains will become unbearable, while the opposite is true: By this point of the fast your stomach is typically not even growling anymore.  Its mind over matter.

At this point, it probably makes sense to underscore and reemphasize the importance of electrolyte supplementation.  Although I have done a fast without it, it is much easier in better for your body to replete those electrolytes.  It’s typically by this point in the fast that I begin to develop significant lower back tightness, achiness in the hips, and significant cramping pain in my quadriceps–all of which I believe are due to insufficient electrolyte supplementation.  I have found that replacing sodium with Himalayan pink salt (either diluted in water or eaten straight up) and taking a magnesium enriched Epsom salt bath really helps.

Day 5

Paradoxically, the last day is often the easiest.  The finish line is in sight and you have nearly completed something that once seemed impossible.  Barring any setbacks such as headaches or leg cramps, by this point you are typically feeling pretty good and may even have the sensation that you want to keep going.  I for one typically do not.  In fact, by this point I am really looking forward to a delicious “break-fast” meal.  And that’s a good thing, because now is the time to start thinking about how you will break the fast and begin refeeding.  You may read about refeeding syndrome, which is extremely rare for a 5 day fast, but is a real phenomenon and can be very dangerous. 

But before we get to refeeding, by this point you may have noticed a few other curious changes in your body.  Your sense of smell will be incredibly heightened.  I found myself driving with the windows rolled up and can easily smell what cooking and the passing restaurants.  Another noticeable effect is the changing pattern of bowel movements.   I typically do not have any past the first day, and many other people report the same thing.  But because we’re all wired differently in this way, you may have a slightly different experience.  Perhaps a more important thing to keep in mind is the changing bowel habits after refeeding, where explosive diarrhea has been reported.  Seriously, do not take this one lightly!

Speaking of refeeding, as you approach the end of day 5 it’s time to slowly begin refeeding.  I have heard reports of people who sit down and devour an entire pizza or steak and get violently ill afterwards.  Don’t be one of them—plan wisely and go easy.  Remember your stomach has not had anything in it other than water or may be coffee/tea for a week.  I typically break fast with a mini-meal of a small salad, bone broth, or macadamia nuts just to see how it goes down, then an hour or so later eat something a little more substantial.  I’ve had a burger in a lettuce wrap or salmon Cobb salad.  It could be whatever you’ve been craving, but after working for 5 days to get into deep ketosis, I think it worthwhile to eat a pretty ketogenic meal on the way out to maintain that state for a little longer, while at the same time replenishing your body’s needs.  Eat something rich in collagen, as some of the weight loss you have experienced during the fast is actually breakdown of valuable muscle and collagenous connective tissue.  And be very careful about carbohydrate intake at this point.  Do not attempt to eat a bunch of French fries or tub of ice cream unless you want to experience firsthand what a massive “insulin dump” into your bloodstream feels like.  Here’s a hint: you’ll end up on your couch sweating and feeling like you are going to die!

Post Fast

If you were struggling with any symptoms of the keto flu, such as fuzzy headedness, headaches , or muscle cramps, we will be pleased to know that these go away almost immediately after eating.  It is actually pretty remarkable.  One thing you will probably noticed this day is that your appetite is a little bit lower and you become satiated with less food.  This is probably one of the biggest benefits of doing a longer fast–it resets your expectations and needs.  You realize that you can survive on less, and less sometimes more. 

Another thing you might notice if you been weighing yourself daily is that you will regain a proximally half of the weight you lost during the fast within a few days.  This is because much of the weight you lost with just water weight.  Do not be discouraged this is totally normal.

My results:

• Weight is taken first thing in the morning. 
• BHB (Beta hydroxybutyrate) and blood glucose  level taken at approximately 6 PM.