The Fasting Experiment
We did it. We’ve just finished our 5-day water fasting.
In our efforts to improve ourselves, we do controlled experiments like this time and again.
There’s no way to self-optimization without self-experimentation.
These endeavours are facilitated by the fact that it’s a hell of a lot of fun for us.
Think of us, Leon and Till, as your personal human guinea pigs.
We’re driven by our natural curiosity and our strong incentive for tweaking, enhancing our performance, and thus maximizing our potential.
But what’s even more important is that we don’t just randomly do stuff.
Our projects undergo meticulous planning.
We do the research beforehand, create an action plan, keep a diary in which we record the relevant parameters and our observations, and finally, we put it into a coherent overall picture –this contains the three Beasts by Nature cornerstones: scientific evidence, personal experience, and theoretical ideas.
We love this whole process and we want to share our it with you. In every detail.
We offer you our honest (and extensive) personal assessment. Then you can decide for yourself whether or not you want to give it a shot.
In a sense, you can consider us the tasters of lifestyle interventions.
If you like what we do, you can help us a great deal by supporting us on Patreon. With your help, we could do the whole thing more professionally –more time for research, get blood work done, undergo medical tests, and so on.
We want to give you the best insight possible and you can make that happen.
Anyway, enough of the sales pitch already. Let’s dig into our fasting project.
The Rules of the Fasting
We did a water-only fast for 5 consecutive days.
Yes, that means no coffee, no tee, no supplements, no MCT oil, heck, even no chewing gum. Nothing came into contact with our pharynx except water, toothpaste, and a little bit of salt.
We still think that this qualifies as a water-fast, though.
But why such drastic measures?
The thing is, we didn’t want anything to interfere with the fasting-metabolism or the natural circadian clock –no foodstuff, calories, and no xenohormetics (e. g. caffeine) that require processing in the liver.
After all, it’s a water fast.
We kept track of the endeavour by keeping a detailed fasting diary and recording our weight, mood, as well as hunger levels at least three times a day. Of course, we trained during that period and also took notes of it. We plotted the quantifiable data in various charts below where you can find our personal log books as well.
Why Did We Fast? Motivation, Hopes and Expectations
First and foremost, we did it for the sake of gaining experience and challenging ourselves.
But there is also compelling scientific data.
Although most of the evidence is derived from animal studies, which can’t simply be transferred to members of the human race, it’s still intriguing. (If you’re interested, I’ve written about the spirit and purpose of intermittent fasting here.)
Some researchers propose that it takes a multiday fast to trigger similar effects in humans.
Whatever the case, we thought that there’s no harm in trying for ourselves (or is there?).
We have nothing to lose. Expect some weight, maybe. And, yes, we are aware of the fact that we’ll probably lose some muscle mass.
At best, we even reap some of the beneficial effects –albeit most of them are context-dependent and not per se good or bad– that multi-day fasting is associated with: Autophagy, ketosis, neurogenesis, stem cell-based regeneration of the hematopoietic system and immune cell shift to a young(er) phenotype, enhancing cellular stress resistance, killing old, senescent and premalignant cells, reversing endothelial dysfunction, improving insulin and leptin sensitivity, and many more
We’ll cover all of that and the underlying mechanisms in another upcoming article.
In layman’s terms, we were hoping for a complete cell renovation of our cells.
Old stuff and junk go out, new and fancy things go in.
On a more tangible feeling level we prepared for three different stages:
1. No hunger but symptoms of caffeine withdrawal
2. Hunger combined with symptoms of caffeine withdrawal –> irritability and tiredness, possibly weakness and dizziness
3. “Ketone switch” –> no hunger and contentment
Of particular interest in this context is our first encounter with severe energy deficit-induced ketosis. While it’s true that we both intermittently fast on a daily basis, we think that this will feel much differently. The keto-metabolism takes some time to fully kick in. We’re excited to see how we feel, think and perform during the state of ketosis. Maybe this will even have a transferrable effect on our daily mini-fasts or other projects involving food abstinence, such as faster and smoother transitioning into ketosis.
According to the literature, the “metabolic switch” to ketone-bodies should occur around day two or three.
Let’s have a look at our logbooks to see if we’re on the right track.
Our Fasting Diaries
*”M” stands for mood, “H” for hunger, and “T” for training –all three are rated from 0 (worst) to 10 (best).
7:45 M: 6 H: 1
I’m feeling a little bit dull and dozy. Yesterday evening, I ate a whole bag of M&M’s as well as a pack of Ben&Jerry’s. This is no product placement but it was rather the rash action of a desperate man facing 5 days on an empty stomach. Today’s fasting shouldn’t be a problem though, as I’m used to this duration. I’m a bit nervous and very excited. There’s one thing, however, I don’t look forward to: The coffee abstinence.
12:30 M: 6,5 H: 3
Until recently, I was tired and hungry. Now, I’m feeling okay. I want coffee. This definitely feels different than my daily intermittent fasts although there’s no difference so far except foolishly omitting the black elixir of life –maybe it’s all in my head. I have a slight but noticeable weird taste in my mouth.
15:10 M: 5,5
I’m having a slight headache. I’m feeling dull and slow in my head. Withdrawal symptoms start to manifest themselves.
17:15 M: 5,5
No changes. But the additional onset of fatigue. The day felt weird and I look forward to sleeping it off.
9:30 M: 7 H: 3
I just woke up. I’ve slept 12 hours. So far, I’m doing well. But my stomach feels extraordinarily empty. My hunger levels are quite low regardless. That’s probably because I’m already familiar with longer intermittent fasts (20 hrs+).
12:30 M: 6,5 H: 4
A similar state like in the morning but with the difference that I feel more like eating something and drinking coffee. I’m cold. On my way to the station, I froze my ass off (+6°C).
14:00-14:45 T: 6
Short GST session. Only did two superset-pairings à 5 sets each. I’m not weaker per se but I can feel not having eaten for a long time and especially not having any caffeine flowing in my bloodstream which is very unusual for me. The training itself was more dragging and I lacked any significant motivation to physically exhaust myself. After the training, however, I felt a pleasant warmth traversing my whole body and my mind started to clear up.
Post-training M: 7,5-8 H: 1
17:05-19:30 M: 6,5 H: 4
I feel exhausted, listless and a bit lightheaded. I’m not really hungry but somehow I still desire food.
What I noticed along my fast so far is that I’m not productive at all and my motivation levels are terribly low. No ambition, whatsoever.
Furthermore, when I’m standing up from a lying position, I get quite dizzy. This phenomenon is called orthostatic hypotension and its sporadic onset seems to be common among water fasting practitioners. This happens almost exclusively in the afternoon or evening and not so much in the morning –except on day three.
I was looking forward to this day because I was eager to experience the ketone-switch.
8:45 M: 6,5 H: 2
I’m feeling a little sick. Otherwise, it’s okay. Dizziness strikes again. And I’m a little cold. I feel like a whiny wimp.
10:00 M: 7,5
Still freezing a bit but mood is definitely improving.
12:30 M: 6,5 H: 3,5
Feeling empty. But I can concentrate. Motivation, however, is currently still an alien concept to me.
14:15 M: 8 H: 1,5
Just finished a walk. I feel so much better now –calm, relaxed and content. My heart rate and blood pressure are significantly lower than usual.
16:20-18:20 M: 8 H: 1
I can feel the ketone-switch happening –at least that’s my interpretation. The long walk seemed to have done the trick. My mood is stable and consistently positive and calm. My head is clear and feels pleasantly warm.
20:30 s. o. H: 4,5
Orthostatic hypotension and dizziness when standing up are persisting.
What I noticed is that since yesterday my senses regarding food are sharpened. I think a lot about food and I perceive way more advertisements than usual. But what’s most prominent is that my sense of smell is through the roof. Walking past a bakery is a symphony of cookies, sourdough, and cinnamon.
08:00 M: 7 H: 1,5
I feel fine but also weak somehow. In front of the mirror, I’ve eagerly tried to stick my belly out. This was a hilariously pathetic attempt which did not result in the completion of my goal. “Breathing into my stomach” also doesn’t work. I think my stomach is the size of a medium orange by now.
10:00 M: 8 H: 1
Full of anticipation for the feast tomorrow, I went shopping for groceries. I’m really looking forward to breaking the fast. I think I’d feel more like a 9-10 if my stomach wasn’t so empty –I’m not hungry but I can sense that somehow. It’s so much psychology and habits. Much of my productivity is contingent on coffee and meals.
12:30 M: 8,5-9 H: 0,5
Since yesterday I don’t have a thirst for coffee anymore. While walking to the station, I felt amazing –the best so far. Nevertheless, I do feel weaker even during light exercise. But mentally I’m not impaired by the fast if not the opposite. My thought processes are very clear.
15:00 T: 7
Training was tough and cumbersome. I felt drained. I want my glycogen stores back! But I did make progress in every single exercise. I didn’t sweat at all during the training.
18:00 M: 8 H 3-4
Soothing calmness. But I’m a bit hungry. Probably because of post-workout being an unusual time for me not to eat.
Day three and day four were the only ones where I didn’t have any bowel movement at all. What’s also caught my attention is the complete absence of any stomach rumbles and farts. Not even one. This is kind of self-explanatory because your digestive track and the resident commensal bacteria have nothing to work with. But I still thought this was worth a separate mention.
08:30 M: 8 H: 1,5
Today’s the day! I’m feeling good and look forward to my first meal since 5 days.
11:40 M: 10 H: 0
Just finished writing my Instagram-post. I’m extremely happy right now! I think, to mark the occasion, I’m going to drink a cup of coffee.
12:00-14:00 M: 11 H: 0
Had the coffee. Awesome. This is the most alert and motivated state I’ve been in for a long time. I’m full of zest for action!
14:30 Training: 9-10
Had a very good gymnastics training session. Made solid progress. Coffee and ketone bodies are a great match.
17:00-bedtime Breaking the fast
Meal One – Smoothie and Sauerkraut
The smoothie’s ingredients: Spinach, apple, ginger, and lime juice.
The first meal was intended to boost digestion while not overwhelming the body with a huge calorie influx. Something light, just enough to get the digestive track going.
Sauerkraut, ginger and lime juice have always helped me digest food better and they also contain a variety of enzymes that help your body absorb nutrients more easily.
I could give you a long list of the benefits of each individual food item and why it’s so smart to break your fast with these.
But, to be honest, my decision to start with these particular things was based on desire.
I just really wanted sauerkraut and a green smoothie.
Note: It’s an odd feeling to consume something with more substance than water.
Meal Two – Big Hearty Salad
The salad’s ingredients: Spinach, kidney beans, bell pepper, scallions, tomatoes, cucumber, carrots, avocado, feta cheese, salmon, chilli flakes, garlic, olive oil, balsamic vinegar.
The second meal was amazing. It was ridiculously satisfying and the flavour was staggeringly intense. My perception of taste is way more sophisticated than usual.
It might not have been the best meal to break your fast but I didn’t really care.
The driving factor for this choice was, again, desire.
Since the start of this very day, I pictured a big hearty and colourful salad with plenty of protein and good fats. I think that I even dreamed of this last night. My body knows best.
It was quite difficult actually to eat the whole thing despite the desire to do so. I was completely stuffed rather quickly. My digestive track has to get used to processing food again.
Note: In retrospect, eating again felt kind of weird –almost exhausting.
Meal Three – Porridge
The porridge’s ingredients: Oats, banana, dates, goji berries, flax seeds, walnuts, coconut flakes, whey protein, cocoa powder, cinnamon.
After waiting for the satiety to pass, which didn’t take too long, I treated myself to a sweet and savory porridge.
And that was it for the day.
Note: Quite a measly calorie yield, at least for me. I was fully satiated, regardless.
Aftermath: After I finished the fast, I travelled to my hometown to spend some time with my family. I think it is a well-known fact that eating healthy can get quite difficult under these circumstances. I had an unquenchable hunger and spend much of my free time scavenging the kitchen. But perhaps this was just a natural reaction of my body: Take what you can, give nothing back. As a consequence, I gained my weight back rather quickly and also a substantial (at least to my personal eye) amount of body fat. This also fits the thrifty gene theory but that’s another story.
The black dot in the mood curve marks the experienced keto-switch.
It is the first day. Since I’ve only eaten one meal a day for a long time now, this day should be the same.
No, it is not! I have a headache. No too bad but still not nice at all! I also have cold extremities. Normally I notice slightly colder hands only in the afternoon. Now, at 10 am, I can already find myself wearing socks and a thick hoodie.
I want coffee, please…
While riding my bike to the gym I realized that my feelings and mood changed solely through my thoughts. My mind realized that there will be no food at the end of the day and made my body switch to eco mode. This realization was like a switch! The outcome was instant happiness and motivation.
The training (full body) was great. I was strong and felt full. Meeting friends at the gym upped my mood even more. Back at home I immediately went to bed. Not eating was actually a bit weird.
I woke up late today with a total of 11 hours of sleep. Regeneration might be a bit impaired… My lower back feels 70 years older. My brain is also not working as it used to. I am a bit lightheaded and there is a slight feeling of dizziness.
Okay, I feel even more lightheaded. It got better on the way to the gym, like on day one.
I knew it before but this training proved me right! Your training surrounding has a
huge impact on your performance. After I arrived at the gym I had good conversations and met dozens of friends. The dizziness was blown away and the training went great. I have to note that my performance in higher rep ranges was slightly impaired. That should be the result of empty glycogen stores. This session felt like a substrate switch of the brain from glucose only to glucose and ketones. My thoughts were finally clear again. By the way, I had still no hunger or desire for food.
Halfway through. I woke up after 10h of sleep. There was no dizziness and I was not lightheaded. The keto-switch from yesterday was proved, at least for me. But I really felt exhausted this day. My legs and arms felt heavy.
I feel better. The exhaustion in the morning might have been related to a lack of
fluid. I drink way less during the fast, around 4 litres.
The good training sessions of the last two days in mind I drove to the gym and expected a
Well, this training was not even a candle… I was not particularly weak but completely exhausted. So exhausted, that I even had to cluster my normal sets to reach the planned repetition range. Actually, I think that not fasting itself was the reason. Today I went to a different gym with a different atmosphere. It is less full of energy, quieter and a kind of “Instagram-celebrity” gym. The most important message for me:
“You are shaped by your environment”
Note: My skin (especially my lips) and hair have dried out completely.
I feel like a tank drove over me last night (8 hours of sleep). Let’s try to get some desk work done.
It is not really working. I can’t concentrate and meet my worst enemies, Instagram and Facebook, way too often.
The worst moment has come, I felt so cold that I took a hot shower for at least 30 minutes. After that, I made the bad mistake to slightly touch my bed. It grabbed my arm and pulled me under the blanket. I was trapped in my own misery. But shortly before I fell asleep, my roommate came home from work. I could escape the dangerous situation and was greeted with a lovely “You look like a ghost”. Upon this, my HPA-axis went through a reboot and I found myself on the bike in the rainy streets of Copenhagen.
I just came back home from the gym. To actually train was the best decision of my life. Again. Humans matter. At arrival in the gym, I was immediately asked by a friend to spot him while he was attempting a PR in the squat. Meanwhile, Isaw another friend doing parallettes handstand-pushups in the background. This kicked me back into the zone. I went for heavy bench press and broke my own personal record –five singles with 132.5Kg. I think I do not have to mention how I was crowned as the happiest guy of Copenhagen later that evening.
Note: I had some trouble with higher rep ranges again!
The day of satisfaction has come. I woke up in the best mood you can imagine. A combination of being happy over how the last training went and the general joy of life –plus the prospect of eating again.
Today I could focus on everything. Mental work was as easy as scrolling my Instagram feed. I even had an additional stretching session this day. I could finish my programming work for the next training cycles and went to the gym where I had my first coffee after four days. The smell and taste was overwhelming and it was followed by the deepest focus you can imagine.
That was it. Five training sessions without food of which the last was the greatest.
I had a wildcard day. The means free exercise selection. You might think I just threw some arms and chest, right? Nope. I went for a combination of calisthenics and strongman training. Full body as usual and finished with heavy lunges.
Note: I felt a bit of joint pain.
Guess what!? It is time to eat. I broke my fast with three small meals: The ingredients are listed below.
Ingredients: Yoghurt with acidophilus culture, kiwi, pineapple, mandarins, dried figs, coconut rasps and cinnamon.
The protein-digesting enzymes bromelain (pineapple) and actinidin (kiwi) might have improved protein digestion while cinnamon might have had a positive influence on blood sugar control. And, let me tell you, I really wanted some mandarins –no function next to satisfaction. That’s why mandarins might have been the most important ingredient of the meal. If your body craves for something healthy, you can be sure that it is in need of it or something that’s inside.
Ingredients: Fried eggs, sardines, feta cheese, yellow bell pepper, garlic, tomatoes, carrots, herbs and chilli.
The eggs were the second thing my body really wanted to have. Cholesterol intake to aid hormonal synthesis might be one explanation. It could as well just be the energy and nutrient density.
Ingredients: Oats, cocoa, apple, pineapple, pear, dates, some more yoghurt and cinnamon
It might be beneficial to have some indigestible fiber to decrease stomach emptying and improve blood glucose control.
The black dot in the mood curve marks the experienced keto-switch.
Our weight loss:
Yes, we lost some fat but the main contributing factors to our weight loss were water, glycogen and GI-content. The weight bounced back quickly after we’ve started eating again. Maybe there was also some glycogen supercompensation afterwards.
What We’ve Learned
Fasting for 5 days was quite the experience. I would even go further and say that it was a great deal of fun. It feels like a complete reset for your body and mind.
It’s just incredible what the human body is capable of.
What was very interesting for me was the first-hand experience how your body shifts into “starvation-induced” ketosis. I’ve never made any experience with ketosis beforehand. Particularly not with the one that is facilitated through complete food abstinence rather than by gulping down oil.
I suspect the ketone-bodies drove my opportunistic food-seeking behavior which began at day three.
The mechanism is well thought out: You have an unquenchable urge to move, a clear focus, and a significantly suppressed appetite so that you don’t become desperate. But at the same time your senses are sharpened and aimed at opportunistic food acquisition –i.e. when food is near, you’re going to have an easier time perceiving it (through smell or visual cues).
The first coffee, as well as the first kiwi and liquid egg yolk, were the best taste experiences in my whole life. Solely for this, the five days of fasting were worth it.
The by far most important lesson for me was that the combination of the right mindset and environment enables you to achieve more than you thought was possible. Keep in mind that all the results you will ever get are based on multifactorial variables. It is almost never just one reason.
In summary, the fast was a very exciting, and above all, a completely new life experience for us.
To be honest, the fast was way less difficult than we’ve imagined. Our hunger levels were each tolerable to non-existent.
We don’t want to lie to you.
The fast didn’t require high mental resilience from our sides and it didn’t really test our willpower. We might have had a tactical advantage because we’re used to going through the day on an empty stomach.
But that doesn’t mean that we didn’t learn any valuable lessons about ourselves.
Humans are creatures of habit. When you take a habit away, like consuming food, things are going to feel weird at first.
But after a while, you can face things with a stoic equanimity –in a good way.
You see things from a new perspective without distractions or means of escape.
During fasting, you also can’t compensate for boredom with eating.
You are alone with your own thoughts.
And that’s actually quite a nice feeling for a change.
Will we live longer now that we’ve fasted?
Well, we think the overall context of our future lifestyle –the way we live the rest of our life– is far more important.
But we also think that integrating fasting protocols into the right context might offer some unique benefits.
Are we sure about that? Not at all. Maybe the exact opposite happens.
Will we do it again? If so, what would we do differently?
But we’re also intrigued to try other, even longer, fasting protocols.
Next time we would also like to get blood work done to give you some references and quantify the results.
Further measured values of interest would be blood ketone levels, blood glucose levels, and the calculated glucose/ketone index.
Do we recommend that you fast?
This is a question we can’t give you an answer to without knowing more about you and your personal circumstances or goals.
Please consult a physician before trying to fast.
But if you decide to do a multi-day fast: Stay busy, socialize, enjoy your new free time, but also seize the opportunity to be alone with your own thoughts.
Drink sufficient water. Supplement with salt if you feel the urge to do so.
That’s it. Fasting is simple. Just don’t eat. And if you’re really serious about it, drink nothing but water.
It’s possible that you experience the following: Cold extremities, dizziness, exhaustion, mood fluctuations, and hunger. Nothing to worry about, unless anything persists.
Take care. And, as always, don’t be stupid.