Intermittent Fasting — A Power Tool for Dieting and Wellbeing

What Intermittent Fasting is, history and science behind fasting, benefits and downsides, nutrition, how to do it.

This article is also available on Medium.

18 min read

autofagia, paasto, autophagy, fasting,

People are often looking for fast and efficient ways to lose weight as to be in shape. There are constantly new and different trends and beliefs of how to train, different diets, what to eat and what not to eat.

One topic that has gained popularity over the past years, and not only in the world of fitness, is Intermittent Fasting (IF).

For those still looking for the magic pill that will solve all issues regarding dieting and training, disregard this article and keep looking. You’ll not find it, as a quick solution doesn’t exist.

But those who are interested in what I would describe as a power tool for dieting and wellbeing, please read on.

The purpose of this article is to tell you everything you need to know about Intermittent Fasting. Here I will give an insight of what IF is, present the history and science behind fasting, introduce different types of IF, discuss briefly about nutrition, display the benefits and downsides related to IF and give instructions on how it is done in practice.

New approach for something old

Intermittent fasting, or IF, is a relatively new way to do something very old, fasting. Throughout human history, people have been fasting due to medical and religious reasons and now IF has gained popularity as a tool to lose weight, save time, and for other health benefits.

IF is not a diet per se, instead it is a pattern of eating. In other words, IF does not define what you eat, but when you eat.

Traditionally people tend to restrict calories by eating smaller portions or by restraining from specific foods.

However, being on a strict diet that either specifies what you should or should not eat or relying on a calorie-restricted (CR) diet by eating many smaller meals per day can be hard. Especially in the long term as cravings tend to get overwhelming and people only have so much willpower.

Eating fewer calories than you consume is, and will be, the main reason for weight loss but with IF you can at least, in theory, get leaner and burn fat by restricting only the timeframe for eating, and not how much you eat.

In general, for dieting IF can be a solution or a helpful tool for some people, as it is easy to get a calorie deficit by restricting the timeframe allowed for eating and by cutting meal frequency. Additionally, by adjusting what and how much you eat, the outcome will obviously be better.

To truly understand IF and the science behind, this article explains what happens in our body during fasting, and among other things how this can be utilized in losing weight. The article further explains how our body gains, stores and consumes energy as well as why different macronutrients and when you eat them play a role. Finally, the article lists different types of IF, describes other health benefits that IF can offer and gives tips on how to get started with this method.

Before starting the journey, below is a quotation from Brad Pilon, the author of the book ‘Eat Stop Eat’, whose mindset on the simplicity of doing fasting instead of old-school dieting is eye-opening.

“The actual act of dieting is very difficult because you still have to eat every day. So every couple of hours you are making a decision about food. The thing I like about fasting is you do not have to do that,” says Pilon. “I like to use the analogy of an on–off switch instead of a dimmer.”

Brad Pilon, author of Eat Stop Eat

History of Fasting

A common belief is that we should eat many small meals throughout the day to keep the metabolic rate high. Hence the idea of fasting might seem weird or even frightening.

But here’s a wild card for you: what if the human body is very used to not eating all the time, maybe even made for it? As to understand the reasoning for this statement, let’s have a look at history. Homo Sapiens evolved around 200 000 years ago long before all the seven-elevens and fast food chains serving quick resolutions for the hungry bypassers.

autofagia, paasto, autophagy, fasting, evolution, hunter-gatherer
Our ancestors did not have access to food all the time. Food was eaten when it was available. 

So, before food became ubiquitous, time and effort were put in to forage all the food, not to eat five times a day. Sometimes food was available only once a day, other times you might have to go a day or two without nutrition.

Simply, food was eaten when it was available, and it wasn’t all the time.

Then around 12 000 years ago the agricultural revolution occurred. This revolution was one of the reasons for cities and villages to evolve and food became slowly easier to obtain. Nowadays food is easily available all the time, but history strongly suggests that eating around the clock is not our natural way of living nor a necessity to survive.

Someone might argue that our body should be quite used to not eating all the time.

And here fasting steps in. But what is it?

What is Fasting?

To make it simple we can assume two timeframes, one as eating and the other one as not eating. The timeframe when we’re not eating for a given period is called fasting.

Fasting can then be split into two main types: one is dry fasting where no food or liquid is consumed. The second type of fasting is water fasting where water, coffee, and tea are allowed.

Once you have been fasting for some time you can reach a ‘fasted state’ that can be beneficial to health. Let’s have a closer look at the science behind.

We use glucose in the liver as an energy source. But when fasting, our body flips our metabolic switch to utilize fatty acids and fatty acid-derived ketones instead of glucose from glycogenolysis.

The flip occurs when glycogen stores in our liver are depleted and fatty acids are mobilized.

Now here comes the good part, in short, this means that our body and brain start to use fat as the primary energy source instead of glucose. You use fat as fuel to think and move.

The amount of time before this metabolic switch occurs depends on the liver glycogen content and the energy expenditure during the fast, but it typically takes around 12 to 36 hours. Other things equal, we can burn fat without changing our calorie intake.

So even if your lifestyle and calorie intake would remain the same, by fasting fat can be burned. And for those who also reduce calorie intake as to lose more weight, here’s a piece of good news: as our body switches to use fat as primary source of energy, the free fatty acids (FFA) serve to preserve muscle which suggests that by fasting it is easier for us to lose weight without losing that much muscle.

As the main point for many who are trying to get rid of extra weight is to get rid of fat and not muscle, fasting seems like an ideal choice.

Once we understand the history and science behind fasting the common belief that we must eat many times a day starts to dissolve. It can be hard to accept this at first but give it some thought.

Ask yourself, did evolution shape us to be dependent on eating all the time even when food was scarce?

Different types of Intermittent Fasting

Now that we understand the origin and science of fasting, let’s have a look at the different types of IF. Some might be easier to start with, some are a bit more challenging. It’s worth mentioning that one type might suit you and your lifestyle better.

But before looking at the types let’s clarify a belief regarding breakfast. Many have probably heard that “breakfast is the most important meal of the day” and that it’s effective in preventing weight gain.

In truth, there’s actually very limited evidence for these kinds of statements.

autofagia, paasto, autophagy, fasting,
Breakfast. Is it really important? Do we need the sugars and carbs from a breakfast seen above first thing in the morning?

Skipping breakfast might not be a bad idea at all. Keep this in mind as you go through the different types below:

Eat-Stop-Eat: 1–2 times a week you fast for 24 hours. Otherwise, you eat normally.

The 5:2 diet: During two non-consecutive days consume only 500–600 calories. The rest of the week you eat normally.

The Warrior diet: 20 hours of dieting with a 4-hour eating window. The frame is modeling a Warrior-lifestyle, where you eat little during the day (small snacks and fluids are allowed) and have one large meal at night.

The 16:8 method (Leangains): An eating window of 8 hours followed by a fasting period of 16 hours. The window for eating can be any time of the day but skipping breakfast and breaking fast at noon is a preferred approach if you have a nine-to-five job. It’s also a relatively easy option to continue fasting after the night and save eating for later. To dive into the depths of Leangains visit

Bulletproof Intermittent Fasting: 6-hour eating window and 18 hours of fasting. Coffee with healthy fats are allowed and recommended before you break the fast. The idea is to improve mental performance and increase protein synthesis by consuming coffee including MCT oil and Grass-Fed Ghee butter. MCT oil is not stored in the liver the same way as other fats, and while fasting it can help in getting into ketosis.

Understanding what happens in our body during fasting and the different types of IF are essential if you want to give it a try. Even so, what really matters, dieting or not, is the nutrition itself.

Nutrition is extremely important and affects our energy levels and mood. Combining fasting with a good and smart diet will yield much better results and it’s also healthier than eating processed food or fast food.

So read on to understand why and what we eat and how often plays a role and combine this information to make fasting as effective as possible.

The Role of Macronutrients and Meal Frequency

To keep our body and mind going we need energy. The three main energy sources for humans are carbs, protein, and fat and additionally, we need vitamins and minerals.

The three main sources are collectively called macronutrients (or macros). Different vitamins and minerals are called micronutrients.

When we eat, energy is extracted from the food and stored in our body for consumption.

Our Total Energy Expenditure (TEE) consists of three different factors which are

  • The Basal Metabolic Rate (BMR, energy expenditure at rest)
  • The Energy Cost of Physical Activity and
  • Thermic Effect of Food (TEF), also called Diet Induced Thermogenesis(DIT).

Out of these three factors, BMR is the major one and accounts for 60–75%. Daily physical activity varies a lot between individual, whereas DIT is the smallest factor and accounts for approximately 5–15%.

The interesting part is that by choosing what you eat and how often, you can have an impact on DIT. Let’s have a closer look at what it is and how it works.

Diet Induced Thermogenesis and Macronutrients

When you eat, the nutrition cannot in its plain form be used as energy. It requires a process to convert the meal into usable fuel for your body. The energy is dissipated as heat after a meal.

This activity, like many other things in life, has a price tag and the currency is burned calories.

Yes, every time you eat, you burn some calories. The saying ‘You have to spend money to make money’ applies here as well. Just switch ‘money’ with ‘energy’.

And here we’ll introduce Diet Induced Thermogenesis: It is the price your body pays for processing calories you have consumed for use and storage.

Two interesting factors play a part in the pricing. Let’s check these out.

The first noteworthy part is that all macronutrients have a different DIT rate, a different price your body pays for them to be processed.

DIT Rates

  • Protein 20–30%
  • Carbs 5–10%
  • Fat 0–3%

The variance is affected by the source of the macronutrient among other things. Further can be found from DIT rates.

autofagia, paasto, autophagy, fasting,
Diet Induced Thermogenesis: the price your body pays for processing calories you have consumed for use and storage. Essential in Intermittent Fasting.

Here’s an example to clarify what it means:

Q: You eat a meal consisting of high-quality source protein worth of 100 calories. How much is your calorie intake?

A: Due to DIT you only get 70–80 calories of the total amount consumed as 20–30% is “lost” due to DIT. You just burned calories by eating protein!

When you look at the nutrient content of foods, what you see, is not what you get. If you are counting calories, this fact is something you should consider.

By eating food with a high-rate DIT, you can eat greater portions which yield greater satiety.

And if you are on a diet, satiety is crucial.

Being hungry all the time will most likely backfire at some point and you’ll end up binge eating. In the long run, cravings will beat most of us.

And protein is the hero of the day, as it has the following perks:

  1. It is the most satiating macronutrient
  2. It preserves muscle
  3. It has the highest DIT rate.

The point here is that one should eat a lot of high-quality protein.

But what about the belief of too much protein being bad for you, especially for your kidneys?

High protein intake

First, let’s try to define a “high-protein intake”. Let’s not use percentages to describe what is high and what is low, as the outcome might vary a lot if your calorie intake consists of 1500 calories vs. 4000 calories.

The intake should be measured as the amount of protein consumed per unit of body weight.

A study of a high-protein diet over a one-year period suggested that a high intake should exceed 2.0 g/kg/d. In this study, it was noted that an eight-week period of having a protein intake of >3.0 g/kg/d (coupled with resistance training) improved body composition and it had no harmful side effects.

The conclusion of the study was that a high-protein diet had no harmful effects in males with years of experience in resistance training.

Another study on healthy persons found no significant detrimental effect on kidney function after centuries of a high protein Western diet.

It is worth mentioning that restricting protein intake is favorable if one is having some kidney disease, but on healthy individuals, a high-protein diet seems to be fine.

We should leave behind the old beliefs of “too much” protein being bad. But do pay attention to the source of protein and food in general, i.e. eating too much red meat is not a good idea and the DIT rate of processed food is negligible.

Meal Frequency

The second interesting factor that affects DIT is meal frequency. It’s true that every time when food is consumed, the metabolic rate rises.

But a systematic review of DIT concluded that having the same energy intake from one big meal instead of several small ones led to a significantly higher DIT.

In plain English, this means that you burn more calories by eating fewer times a day.

Studies indicate that DIT is higher when eating one to three times a day compared with eating more than three times a day.

Although DIT is the smallest factor of TEE, in the long run, it makes a difference whether it’s 5% or 15%. Think about the difference for e.g. one month, a variance of 10 percent can have a significant effect on whether you’re going to lose or gain weight.

autofagia, paasto, autophagy, fasting, DIT
Diet Induced Thermogenesis: energy is dissipated as heat after a meal.

Few more points that might be of interest. DIT rate for alcohol varies between 10–30%. So, if you do occasionally have a drink or two and are counting calories, you can maybe have a bit more than you first thought (just do not combine it with fatty foods). Obviously, take into consideration all the negative effects of alcohol which will not be discussed in this article.

The other point, a good reason for enjoying your meal slowly and remembering to chew it properly: studies comparing eating fast vs eating slowly have shown that consuming a meal slowly yields to a higher DIT.

To sum it up having a high-protein diet and eating large meals a few times a day combined with intermittent fasting is a relatively easy, safe and effective way to maintain or lose weight.

Now we have discussed the role of food and how you can optimize your IF by taking these factors into consideration. Next, we’ll have a look at other benefits that are related to fasting.

Other benefits

First, it is relevant to mention the benefits related to time and simplicity.

If you choose to eat only a few times a day compared to having several smaller meals, the benefit of saving time is quite self-explanatory.

What’s more, you mitigate the risk of eating more than you consume. Besides these, there are many benefits backed by science that are related to IF, many of which can extend not only our life span but our health-span as well (the time of our life when we are healthy and disease free).

One of the most important benefits is a physiological process called autophagy.


In 2016 Dr. Yoshinori Ohsumi was awarded a Nobel Prize in Physiology or Medicine for his research regarding autophagy, which is a natural process where the body degrades and recycles damaged cells, proteins and toxins to maintain cellular homeostasis (balanced cellular function).

The process can naturally neutralize cancer cells and degrade cells which have been infected by bacteria or viruses, it slows down the aging processreduces inflammation and gives your body’s ability to function a boost.

Dr. Yoshinori Ohsumi used starvation in his studies to trigger the process, but the interesting part is that it also happens during calorie restriction and fasting.

Here it is worth mentioning, that there is a difference between using IF as a tool to lose weight and in using fasting to achieve autophagy. If you want the benefits of autophagy, you have to be more aware of what make break the fast.

autofagia, paasto, autophagy, fasting,
Diet Induced Thermogenesis: energy is dissipated as heat after a meal. You can affect the rate of DIT.

Gaining benefits just by choosing a timeframe for eating seems like quite a simple way to give our health a boost. It must be mentioned that some of the below-mentioned studies have been done on rodents and more studies and experiments are needed on humans to verify whether the same benefits apply to us.

Still, it is already highly motivating to employ fasting as several studies suggest that IF can benefit our brains in general, cardiovascular health and improve our cognitive abilities.

Additional benefits

Besides the above-mentioned benefits, IF can:

· Prolong your life

· Reduce the likelihood of getting sick

· Promote cardiovascular health

· Decrease cancer risk

· Decrease risk for diabetes

· Boost mood and motivation

· Improve learning and memory

· Improve sleep

· Enhance your cognitive abilities and protect neurons against genetic and environmental factors when aging

Above mentioned possible bonuses for doing IF have a pretty pleasant ring to the ear and we can only wait that more studies are done.

Let’s move on to recommendations and simultaneously have a look at the downsides before finally going through how to start doing IF, if one would wish to do so.

autofagia, paasto, autophagy, fasting,
Be smarter? Intermittent Fasting can benefit our brains.

Recommendations and Downsides

There has not been found any significant reason for normal healthy people to not give IF a try. Still, there are some downsides to be mentioned and some recommendations to take into consideration.

First, IF is not recommended during pregnancy, if you’re suffering from depression and for people under 18 years old.

If you have a history of or have an eating disorder, it’s highly recommended to consult a doctor first. Also, you should note that if your diet is already more on the poor side to start with, then you might not get enough nutrition which could lead to the loss of muscle mass or other health issues.

autofagia, paasto, autophagy, fasting,
Intermittent Fasting is not a magic pill.

It’s recommended to ensure that you get enough calories even if you are dieting, to eat whole foods, avoid processed food, to eat enough proteins and vitamins and doing some strength training if you want to give IF a try.

Additionally, if you already have a very low fat-percentage and lose more weight, the testosterone levels can decline rapidly (at what fat percentage your testosterone levels decline rapidly is individual, but this occurs at some point when below 10% body fat). For women, there might be issues related to the menstrual cycle and it’s suggested that women have a longer eating window than men, around 10 hours is preferred to 8.

For some people it takes more time to adjust to a new habit, some do not adjust at all. For example, if skipping breakfast makes you irritated the first week(s) when trying IF, that’s fine. But if it just goes on and on, you lose focus and have bad headaches, then don’t skip breakfast.

The human body is complex, and one thing does not suit everyone. As mentioned at the beginning of this article, IF is not a magic pill that solves all issues.

Finally, social norms are a big factor as well and can lead to a downside. Skipping events, parties or other social events because of the way you eat? This can be very tricky and hard to combine when trying to have a normal life as well. Here, finding a balance is the key, and not missing out on all events is a good idea, however, are all the events and parties worth attending?

autofagia, paasto, autophagy, fasting,
Do not ruin your social life. But don’t ruin your life with too much partying.

How to start

Now you have quite a lot of information and can choose for yourself whether you’d want to give IF a try. If you have decided to go for it, below are a few key points and tips to get one started.

Just remember, adjusting to something new requires some time and effort.

1. Set a goal: really try to think why you want to give IF a try. Clarify a goal, figure out how reaching the goal will benefit yourself and others, write everything down. This will help you to be persistent and not give up. About that:

2. Be persistent: some people might adjust fast, for others, it might take a month. Do not give up too easily and if needed, start slow. If you have a well-defined goal and have thought about how it can change your life, it will make things much easier.

3. Track your progress and measure: at least track your weight if you are trying to lose some. Plan ways to measure results as it will motivate you. Measure things that will help you reach your goal! For example, track your workouts and count how many times a week you exercise. Measure how much extra time you have for other activities as you do not have to think about food all the time. The important part is that you track and measure your progress.

4. Choose your IF type: As the human body really likes regularity, choose one of the types of IF that might work for you. A relatively easy-to-maintain approach is the 16/8 method as it gives you consistency.

5. Eating window: Pick an eating window that suits you and your lifestyle the best. For i.e. 9–5 workers starting their eating window around 11 am — 12 am and closing it around 7–8 pm is a good idea. Do not get too obsessed about the window, even if it’s someday from 12 am to 7 pm or another day from 11 am to 8 pm, doesn’t matter. The point is to have the somewhat same rhythm in the long run. Meetings, school, some events, and other factors will make it nearly impossible to keep the exact same time for the eating window.

6. Meal frequency: As mentioned our body likes consistency and people tend to get hungry at the same times of the day, hence it is a good idea to have the same meal frequency. Two or three meals a day is preferred (with no snacking in between) to keep DIT at a high level. Eat large proper healthy meals and eat plenty of protein. Avoid processed food!

7. Training: You can train in a fasted state, during the day or in the evening, but eat your largest meal of the day after training. If you choose to train in a fasted state and have been fasting for 12–16 hours, consider taking some BCAA before and after training until your first meal as to preserve muscle.

8. Sleep: is extremely important, and whatever you are doing, try to make sleep as good as possible. Sleep is something not to be neglected as it works as the base of the pyramid the energizes you. When people are tired they tend to eat more, prefer unhealthy food, skip the gym and be inefficient in whatever activities they are doing. Choose your eating window in such a way that you have a few hours before going to bed. It depends on people, but some might find it hard to fall asleep when completely full and if bloated. Also, eating too heavily before going to bed might lead to your resting heart rate to not drop to optimal levels during the night and this can affect your sleep cycle and the different stages of sleep, particularly deep sleep.

Now you hopefully have learned about the background and science of fasting, about different types of IF, about macros and meal frequency, other benefits related to IF and how to start doing it.

Remember that IF is not something magical that works for everyone and which resolves all problems. But if it suits you it can be a very powerful power tool for dieting, for time saving and for health in general.

Follow me on Instagram: Kevness100

Lue myös :


Angelica Quatela, Robin Callister, Amanda Patterson and Lesley MacDonald-Wicks. The Energy Content and Composition of Meals Consumed after an Overnight Fast and Their Effects on Diet Induced Thermogenesis: A Systematic Review, Meta-Analyses and Meta-Regressions.  Published online 2016 Oct 25. doi: 10.3390/nu8110670 

Bronwen Martin, Mark P. Mattson and Stuart Maudsleya Caloric restriction and intermittent fasting: Two potential diets for successful brain aging Ageing Ageing Res Rev. 2006 Aug; 5(3): 332–353. Published online 2006 Aug 8. doi: 10.1016/j.arr.2006.04.002

Dave Asprey, Bulletproof Intermittent Fasting: Lose Fat, Build Muscle, Stay Focused & Feel Great

Fernanda Antunes, Adolfo Garcia Erustes, Angélica Jardim Costa, Ana Carolina Nascimento, Claudia Bincoletto, Rodrigo Portes Ureshino, Gustavo José Silva Pereira and Soraya Soubhi SmailiI Autophagy and intermittent fasting: the connection for cancer therapy? Clinics (Sao Paulo). 2018; 73: e814s. Published online 2018 Nov 27. doi: 10.6061/clinics/2018/e814s

Godínez-Victoria M, Campos-Rodriguez R, Rivera-Aguilar V, Lara-Padilla E, Pacheco-Yepez J, Jarillo-Luna RA, Drago-Serrano ME. Intermittent fasting promotes bacterial clearance and intestinal IgA production in Salmonella typhimurium-infected mice Scand J Immunol. 2014 May;79(5):315-24. doi: 10.1111/sji.12163

Hussin NM, Shahar S, Teng NI, Ngah WZ, Das SK. Efficacy of fasting and calorie restriction (FCR) on mood and depression among aging men. J Nutr Health Aging. 2013;17(8):674-80. doi: 10.1007/s12603-013-0344-9.

John Douillard Fasting Research Wins Nobel Prize in Medicine. Is it right for you? December 21, 2017

Jose Antonio, Anya Ellerbroek, Tobin Silver, Leonel Vargas, Armando Tamayo, Richard Buehn, and Corey A. Peacock. A High Protein Diet Has No Harmful Effects: A One-Year Crossover Study in Resistance-Trained Males.  Journal of Nutrition and Metabolism, 2016

Klaas R Westerterp. Diet induced thermogenesis. Published online 2004 Aug 18.

Nobuhiko Kojima, Tomoaki Shirao Synaptic dysfunction and disruption of postsynaptic drebrin–actin complex: A study of neurological disorders accompanied by cognitive deficits Department of Neurobiology and Behavior, Gunma University Graduate School of Medicine, Maebashi 371-8511, Japan

Josh Quittner The Silicon Valley Diet Published Nov 11, 2017 in

Michael Breus Can Intermittent Fasting Help Sleep? Dec 18, 2018 | Health, How to Sleep Better

Roger Collier. Intermittent fasting: the next big weight loss fad. May 14, 2013 185 (8) E321-E322; DOI:

Rothschild J, Hoddy KK, Jambazian P, Varady KA. Time-restricted feeding and risk of metabolic disease: a review of human and animal studies. Nutr Rev. 2014 May;72(5):308-18. doi: 10.1111/nure.12104. Epub 2014 Apr 16.

Selfhacked Intermittent Fasting Benefits + Results, Diet, Schedule August 8, 2016.

Siim Land Full Guide to BCAAs and Fasting – Can You Take Branched Chain Amino Acids While Fasting? 2018 Apr 18

Stephen D. Anton, Keelin Moehl, William T. Donahoo, Krisztina Marosi, Stephanie Lee, Arch G. Mainous, III, Christiaan Leeuwenburgh, and Mark P. Mattson.  Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting. Published online 2017 Oct 31

Vázquez Cisneros, López-Espinoza, Martínez Moreno, Navarro Meza M, Espinoza-Gallardo, Zepeda-Salvador. Effect of feeding frequency and schedules on diet induced thermogenesis in humans, a systematic review (original article in Spanish, Abstract available in English). Published 2018.

William F Martin, Lawrence E Armstrong, and Nancy R Rodriguez corresponding author. Dietary protein intake and renal function. Published online 2005 Sep 20.


  4. ttps://
  6. ttps://