From fasting to longevity I. – the trials and tribulations of caloric restriction

Hunger, or fasting. For many people, even a conversation about this topic is something so scary that they automatically develop a grandmother complex and start telling you that you have to stop thinking about “losing weight” and that you should eat regularly.

But is it really so? In this two-part series, we’ll look at the importance of fasting in biohacking, as well as its specific health benefits or risks. In this part, we’ll cover mostly objective measurements and studies, while I’ll leave part two to purely subjective measurements (specifically, my experience with Oura algorithms and the glucometer during fasting).

How does fasting work?

Fasting, or the intentional restriction of caloric intake over a period of time (at least that’s how ChatGPT defines fasting), has a number of health benefits ranging from reducing excess fat, to improving immunity, and promoting longevity.

Fasting takes many forms and variations, which we’ll get to. But how does caloric restriction per se work under the hood?

Well, fasting induces a process called “ketosis” during which the body metabolizes fat into energy. After about 12 to 16 hours of fasting, blood glucose and insulin levels drop and nutrient signaling pathways that are regulated by the protein mTOR kinase are deactivated. In human terms, this means that during ketosis the body goes into a “fasting state” in which it stops using glucose from food for energy and starts making ketones, which are metabolized from fat stores.

Among other things, ketones may not be metabolized from fat stores, but directly from a fatty diet, as long as one gets into a so-called fat metabolism due to the restriction of carbohydrate intake. Thus, one does not have to fast to be in a “fasting” state. But more on that later.

What is the purpose of fasting for an ordinary person?

1. Fat metabolism and weight reduction

We already know that our bodies start taking more energy from fat stores during fasting. However, beyond that, we can also train our metabolism by fasting. We can teach our body to use the fat as a source of energy instead of carbohydrates. And this really comes in handy in many situations – fat is metabolized much more slowly than sugar and doesn’t mess with our glycemic index. The energy from it is gradually released, leaving a longer lasting feeling of fullness and teaching us to be more sensitive to hunger.

In simple terms – imagine two furnaces. Into one furnace you throw a log and into the other furnace you throw a rag dipped in gasoline. The log (fat) burns more slowly and releases heat (energy) more gradually into the furnace. This makes it burn for a long time and we don’t have to keep throwing new logs in to have energy. Conversely, the gasoline rag (carbohydrate) causes a rapid reaction in the second furnace with a huge flame (high glycemia), followed by a rapid drop in energy, during which we have to add another gasoline rag if we want to have heat in the room (that is, if we want to have energy and don’t want to feel hungry/sugar cravings).

This will improve our insulin sensitivity. After all, insulin is the hormone that is used to regulate blood sugar and store excess energy in fat stores. Because our cells are more sensitive to insulin, less of it is automatically needed for the body to function.

Among other things, in a state of ketosis, fat is burned without the use of protein, so we can continue strength training – and grow muscle – even while we eat nothing (or just some fat).

But back to fasting. Personally, obesity doesn’t bother me, but if it does bother you, you’ll appreciate that fasting reduces visceral fat in addition to losing the subcutaneous fat. This fat is found around our organs and if there is a lot of it, it has a significant impact on our health. In smaller amounts, it is beneficial and protects our organs from damage. In higher amounts, it acts as a hormone gland in the body, which is a source of inflammation.

2. Hunger hacking

Of course, if we don’t throw gasoline rags into our “furnace” but logs, the final energy in the furnace is far more stable. If we add a new log to it, we do so in complete peace of mind and not in impulsive fear that “suddenly the fuel in the furnace has burned out and we may quickly freeze”. If we are experimenting with fasting, or if we are merely following a ketogenic or low-carbohydrate diet, we can distinguish true hunger from “carb cravings.” Insulin sensitivity will make us sensitive to gasoline rags and we won’t even have much of a desire for them, as they would upset our balanced energy system.

However, there is other hunger hacking going on during fasting than just hacking through insulin sensitivity. There is also an increased sensitivity of the receptors for the so-called “hunger” hormone (ghrelin) and the “satiety” hormone (leptin). This makes us less hungry and we feel satiated sooner when we eat. This will help to give us better control over our eating.

We will have control over when and what to eat. Our performance will no longer depend on whether we are full or not. With less hunger, we won’t need to immediately look for something to eat to keep our blood sugar from dropping and making us feel weak and sluggish. Over time, we’ll find out how different foods affect us and our performance, and we’ll optimize our diet because of it.

Addendum – excessive ghrelin release, by the way, is a major cause of the “munchies” that many a cannabis user can experience.

3. Brain support

It is already known that in a fasting state, our body uses ketones and not glucose as an energy source. However, when I raved about the benefits of ketosis to Mrs. Križanová, my biology professor in high school, her operating system crashed. She told me that “ketosis is stupid because my brain won’t work during ketosis – in fact, the brain will consume up to 20% of its daily caloric intake, and if we don’t give it glucose (or if we don’t give it any calories at all), the brain will starve.”

Of course, the professor was wrong. Reminding high school professors of their intellectual limitations is not always the best idea, but the bottom line is that the brain does not waste during fasting, quite the opposite. Also, the brain is capable of switching to ketone mode when needed.

Among other things, ketones promote brain activity. The amount of brain-derived neurotrophic factor (BDNF) increases, which makes the brain regenerate, while improving memory, the ability to learn and creating a natural prevention against Parkinson’s and Alzheimer’s. At the same time, if we don’t eat, we are essentially creating time and space for the enzyme systems and microbiome to rebuild without the burden of food. In more layman’s and colloquial terms; we cut off the carb nutrition to the “bad” bacteria and only the stronger and “good” ones survive.

Other benefits

As such, fasting could possibly be responsible for other benefits as well:

  • Lowering blood pressure.
  • Improving pancreatic function.
  • Improving insulin production and increasing tissue sensitivity to it.
  • Improving blood sugar and fat regulation.
  • Reducing of LDL cholesterol and total cholesterol.
  • Preventing the development of type 2 diabetes or its worsening.
  • Increasing the production of HGH (growth hormone), which is the main regulator of metabolic processes, the aging process and also decides the overall fitness of a person (among other things, boosts longevity).

Different disciplines of fasting

Fasting takes many forms, often influenced by culture and religion, but in terms of health benefits, we will primarily focus on two types of fasting – intermittent fasting and 3-day fasting (aka “prolonged fasting”).

Understandably, the main difference between prolonged and intermittent fasting is that prolonged fasting (PF) consists of absolute caloric restriction for at least 72 hours, whereas intermittent fasting consists of cyclical alternation of periods of fasting with periods of eating.

While there is only one method of PF due to its simplicity (based purely and only on cutting out food for a period of time), with IF there are different protocols for cycles of eating and fasting. The most common of these include:

  • Alternate Day Fasting – every other day (e.g. Monday/Wednesday/Friday) you will eat nothing and on non-fasting days (Tuesday/Thursday/Saturday/Sunday) you will eat normally.
  • Eat-Stop-Eat – in this case, a 24-hour fasting period is maintained 1 to 2 times a week.
  • 16:8 – probably the most popular method of intermittent fasting (IF), which I follow practically the majority of days in the year. This method involves designating 16 hours a day for fasting, squeezing your daily caloric intake into eight hours. If you give yourself enough sleep, this fasting method really isn’t hard to follow. However, it also has a stricter version, called “18:6”.
  • Warrior Diet – with this IF method, one fasts virtually all day, eating only one large meal a day (and that in the evening). Personally, this style of eating hasn’t worked very well for me, as having a “big meal” in the evening kicks up my metabolism – and with it my appetite – and that’s not exactly what I need during the evening.
  • 12:12 – this protocol may be best for newbies who need to get used to IF. The name of the protocol describes exactly what it is; you can fast for 12 hours while eating for another 12 hours. If you get used to it, you can go on to a 14:10 regime and then on to 16:8.
  • 5:2 – technically, this is not a fasting protocol, as there are no precise time frames assigned to fasting. On this diet, you will eat a normal diet 5 days a week, then for 2 days you will drastically reduce your caloric intake and only eat about 1/5 of the normal amount.
  • One meal a day (OMAD) – you eat all your daily calories in just one meal each day and fast the rest of the day. Personally, this method suits me very well, but I like to alternate it with a normal eating to overeating regime, as fat stores disappear very easily when applied for a long time (which I can not really afford).

Unlike IF, PF is an extreme form of caloric restriction, but it can last from three days (72 hours) to a week. Fasting is broken only with water, coffee/tea and electrolytes. For people who are new to fasting, it is recommended to practice IFs of gradually increasing duration before trying PF to allow your body to adjust to ketosis (12:12, 14:10 to 16:8).

Health benefits of PF

Prolonged fasting, like any other fasting, can understandably promote weight loss, reduce abdominal fat and improve blood pressure levels. This is true even for those who are already at a healthy weight.

However, PF, like anything else, is no miracle weight loss treatment, and if you suffer from obesity, you need to repeat PF multiple times and incorporate it into your holistically healthy lifestyle in the first place.

PF has the advantage, unlike IF, of inducing autophagy on a much more extensive level. And if you don’t remember your high school biology, autophagy (from the Greek autóphagos = “self-feeding”) is a dynamic cellular process in which cells remove unnecessary or dysfunctional components (or straight up entire cells) through a lysosome-dependent regulatory mechanism. Through this process, the body naturally gets rid of weak and dysfunctional cells or parts of cells. Thus, autophagy is not about any weight loss, but about the health of the cells in your body.

A simple drawing of autophagy. The luminous little sphere that enters and then exits the cell is a lysosome – an organelle used for the hydrolytic degradation of substances coming from the cell or its surroundings. In human language – the lysosome serves to degrade everything that is no longer “demanded” in the cell.

Importantly for fasting, autophagy also occurs during nutritional stress, when available energy sources for survival are being balanced, and can therefore be triggered by caloric restriction. Approximately 24 hours after prolonged fasting, the protein kinase TOR is suppressed in response to nutrient deprivation, which induces autophagy.

It is thought that it is the cell renewal due to autophagy that protects against age-related diseases such as neurodegeneration, cardiomyopathy, diabetes and cancer, and which also increases longevity.

Most crucially, autophagy reaches its peak on approximately the second day of a prolonged fast. And a person maintaining e.g. a 16:8 IF has no chance to get to this peak.

Possible side effects of PF

The obvious drawback of PF is the constant hunger. Given that most PF only allows the consumption of water, tea and coffee, it is a method that requires serious commitment and motivation. However, our body is very adaptable and can adapt to hunger as well. One study found that up to 93% of participants reported almost no hunger during PF.

My personal experience with PF is that my greatest hunger came on the second day of fasting (i.e., during the peak of autophagy), with almost no cravings for food from the third day and above (even while I was baking Paleo Christmas cookies).

And while long-term fasting is generally safe, it is one of the riskier methods of caloric restriction, which can be associated with mild side effects including dehydration, electrolyte imbalances, and fatigue. Fasting participants may also experience irritability and low energy as the body goes into ketosis.

You can expect to be pretty cold during PF, but I, as an example, made it through my 4-day PF fast in December unscathed, largely due to getting enough exercise (I went to techno every day) and consuming plenty of salt dissolved in water. Salt is a really big help during this cold and low energy as it improves blood circulation. Thanks to plenty of exercise and salt, I was functional enough during PF to handle such an extreme as hardening off (I definitely don’t recommend it though).

Health benefits of IF

Since ketosis starts after about 12-16 hours of fasting, you can achieve the same fat burning benefits of prolonged fasting even with the shortest type of IF.

Intermittent fasting has the advantage over long-term fasting in that it avoids the intense feeling of hunger and can be practiced virtually daily. This makes fasting easier to maintain and has less impact on other areas of your life, such as your social life (although I personally had no problem going to technos in the middle of my fast). Practicing fasting daily can actually help to restore a relationship with food, with users reporting a reduction in feelings of hunger, a better perception of the nutritional value of food, and improved ‘well-being‘.

However, since autophagy, depending on the individual, may not begin to occur until 16 hours of fasting, the magical therapeutic effects of cellular restoration are much harder to achieve with IF as opposed to PF.

Finally, on the health benefits of IF, I would like to make one point that I find particularly important – I think it is advisable to end your 16:8 IF fast with exercise. This is because the body has an increased ability to store protein in the muscles after training during IF. Exercise (in moderation) is therefore a really great idea, and I recommend eating your first meal of the IF cycle within two hours of your workout so that you can most efficiently deposit the calories you’ve consumed into your muscles as part of your boosted metabolism.

Possible side effects of IF

IF is associated with minimal risk compared to PF, with mild side effects including headaches and fatigue. However, some users may unknowingly reduce their physical activity before, during, and after the fasting period and overeat during the 8-hour eating interval to compensate for their caloric restriction during the 16-hour period. This effect is especially common in people used to a sugar metabolism a lá “gasoline rag”, which is why I definitely recommend restricting carbs for an extended period of time before you even try IF.

It’s also very important to move and exercise during IF, which is not recommended very extremely with PF. A few minutes spent on the horizontal bar won’t kill you though. It will definitely give you the energy you need and get rid of the feeling of hunger.

Summary and important recommendations

From a biohacking perspective, fasting is a very effective and simple tool that can greatly improve the quality (and length) of our lives. However, everyone’s body is unique. Equally unique is the environment in which our bodies move. Each of us is suited to something different, which is why “listening to your own body” is far more important than following any instruction manual. And this is also the case when it comes to fasting.

If you cultivate your fasting, the process will become totally relaxing for you, which will practically not limit you in anything and will only give you energy or save you time cooking and figuring out what to have for lunch 🙂

If you decide to actively fast, you should take into account the following recommendations to help you reduce all the possible side effects that are usually associated with fasting:

  1. Don’t push yourself. Aim for a gradual change in your lifestyle. Make progress and try to gradually increase the number of fasting hours. But always listen to your body first and foremost. Figuring out that calorie != energy is a long-term and complex process that requires a lot of perception of your own body. Mastering fasting is nothing more than carefully learning all the ways you can work with your own body to cultivate your energy that you don’t already know about (whether by heat, cold, movement, etc.). If necessary, I recommend consulting with a doctor who deals with the subject.
  2. Keep yourself adequately hydrated throughout the fasting period. Hydration doesn’t just mean enough fluids, but also enough minerals. Salt is your friend; I personally recommend Himalayan or sea salt, which not only contains NaCl, but also other important minerals and trace elements.
  3. In the period when you have the time to eat, pay attention to the quality of your diet. For best results, I recommend you emphasize quality protein and limit your carbohydrate intake. This will put you in a state of fat metabolism, where your body burns more fat, you’ll hack your blood sugar sensitivity, and you’ll reduce your need for sweets and snacking.
  4. Hunger is a normal state and doesn’t necessarily give you the command to go to the fridge and get something to eat. If I’ve felt really ravenous hunger during PF, I’ve usually just meditated into that feeling, thought something like “yikes, hungry monkey, how interesting” and moved on. The hunger then disappeared on its own.
  5. You can multiply the effects of intermittent fasting if you indulge in short and intense exercise during this period. You will gain additional benefits such as:
    • Better use of fat stores as energy sources
    • Increased energy during fasting
    • Reduction of the feeling of hunger
    • Improved metabolism and oxygen supply to tissues
    • Increased autophagy

I wish you good luck with your experiments and see you again in the second part dedicated to subjective measurements!