Intermittent Fasting: A complete guide

Intermittent Fasting: “Eat breakfast like a king, lunch like a prince, and dinner like a pauper.” Most likely you either heard it from your parents or have read it in some health magazine. But is this really beneficial for your body? A new diet called intermittent fasting suggests consuming food less frequently and even skipping breakfast, claimed to be the most important meal of the day. Indeed science has found many beneficial effects to occur when fasting. Nutritionists even advise us to incorporate deliberate periods of fasting into our lifestyle, just like our ancestors were once forced to.

Intermittent Fasting
Intermittent Fasting

What is intermittent fasting?

Intermittent fasting involves alternating cycles of fasting and eating and is currently one of the world’s most popular health and fitness trends. Rather than focusing on what food have to be eaten as conventional diets, intermittent fasting only takes into account the time of the meals consumed. As a result, members of intermittent fasting incorporate designated fasting and eating periods in their daily schedule.

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How does intermittent fasting work?

Depending on the method, this period can vary in length. The most common form of intermittent fasting is the 16/8 method, which states to fast for 16 hours and have an eight-hour eating window. Skipping breakfast and having the first meal at lunchtime is the most common procedure. Within the eating window between lunchtime and dinner, individuals eat normally. In the fasting window, non-caloric beverages are allowed such as water, coffee or tea.

Another method is to eat normal 5 times a week and on the remaining days only up to 600 kcals (the average person’s body consumes approximately 2000 kcals daily even when at rest). Another way is the Warriors Diet, where you only have a very short eating window of up to 4 hours. This would mean you only have one huge meal every day. The amount of calories you take in with one meal is therefore significantly higher.

History of intermittent fasting

The concept of deliberately fasting seems wrong to many people because of the belief breakfast is the most important meal of the day. Skipping breakfast is considered unhealthy. At the same time, we have been bombarded with information saying we better eat small meals more frequently than a few large meals to keep blood sugar levels on a constant level. Only recently, people began to challenge this dogma which made it seem this kind of diet to be new for us.

However, contrary to common belief, humans are actually programmed to go on a fast for longer periods of time making intermittent fasting a more natural way of eating than the common 3-meals a day eating schedule nowadays. In former days, when food could only be acquired by hunting, it was not uncommon to be fasting for almost the entire day and only have a big meal as dinner. If food was available it was eaten as soon as possible. At the same time, fasting for more days in a row was common. Our ancestors were not sure when they would eat next, forcing them to indulge even more when food was available. Therefore, without knowing the science behind it, our ancestors were following an intermittent fasting diet.

What happens in the body when doing intermittent fasting?

Our body is only able to get its energy from either the food we consume or from the stored food we have ingested before. However, it is not possible to obtain the energy needed from both sources at the same time. This is the reason why everyone will be in one of two states: The fasting- and the fed-state.

Every single person in the world will experience those two states (also if we are not following intermittent fasting). During sleep, we will naturally fast (unless you wake up in the middle of the night and have a snack). Each state will, therefore, be more or less the same length (dinner at 8pm and breakfast at 8am makes a fast of 12 hours, the rest of the day we are feeding). Individuals who follow intermittent fasting will have their fasting-states prolonged and their fed-state shortened. The intermittent fasting proponents suggest reducing the fed-state window so all the food intake takes place in 8 hours and not the normal 12 hours. Consequently, they will be in a fasting state for longer which has shown to be beneficial due to various processes in our body. The figure below shows what happens in each state in both conventional diets and intermittent fasting:

Insulin levels decrease


– Growth hormone levels increase which have anabolic qualities (helps build muscle)

Adrenaline level increases

– Body fat is burned (the glucose is obtained from the fat and not from the food you eat)

Glucagon (triggers the process of using energy from fat resources) increases


– Insulin levels increase


– Growth hormones decrease

– Adrenaline level decreases

– Fat storage increases (the extra glucose from the food is stored in the form of body fat in the event of having no food available)

– Glucagon decreases

Effects on the brain while being on an intermittent fast

  • Enhanced cognition: In an experiment in which mice were deprived of food, the hormone ghrelin was secreted in larger amounts. This hormone is also secreted in humans when our stomach is empty and signals hunger. The researchers found ghrelin to play a large role in the creation of brain cells. It stimulates the brain cells to divide and multiply, a process called neurogenesis. In an experiment, where ghrelin was directly injected into the brain cells of mice in a dish, a gene was turned on promoting the growth of brain cells. The goal should, therefore, be, to prolong the fasting state in order to increase ghrelin secretion. This is naturally achieved by intermittent fasting.
  • Initiation of vital cellular repair processes: Throughout our lifetime, the production of free radicals is inevitable and with age, they are more likely to have detrimental effects on the functioning of our brain. Free radicals are unstable molecules which are able to react with the cell structure causing damage. In order to live healthy for a long time, it is therefore essential to reduce the number of free radicals by taking in lots of vitamins which have the ability to scavenge these free radicals. Another way to reduce the number of free radicals was found to be intermittent fasting. In a study, the cells of the group which followed the diet made more copies of a gene called SIRT3. The gene was found to play a crucial role in a pathway to prevent free radical production and improve cellular repair processes.
  • Increase of brain-derived neurotrophic factor, or BDNF: This is a naturally occurring growth hormone responsible for the formation of new brain cells. A higher level of this hormone was seen to increase intelligence, mood, productivity, and memory. At the same time, the risk of developing neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease is decreased. To add to the list of benefits, anti-depressant characteristics can also be associated with high levels of BDNF. As you can see, having your BDNF levels increased, turns out to be beneficial for you. Intermittent fasting or even just a caloric deficit, are efficient ways to boost the production of this hormone leading to a healthier life in the long run.

Intermittent fasting and bodybuilding

Intermittent fasting has been gaining more and more popularity in the bodybuilding scene. In the past, however, athletes were scared of losing their muscle mass if they went for longer periods of time without eating (feeding their muscles). It was believed our body immediately starts to break down the proteins into amino acids (the raw material for the proteins) to obtain energy leading to catabolism (breaking down of muscles). This is however not the case and nowadays a lot of bodybuilders follow intermittent fasting while lifting heavy. The reason for this is that when you fast, breaking down proteins is not the preferred source of energy. Fat and carbohydrates, on the other hand, are the macronutrients the body gets its energy from first. This means when you fast, using the stored carbohydrate (glycogen) will be the preferred source. These storages will, however, be used up really quickly and as soon as they are depleted, the fat storages will be used to maintain the body working. In bodybuilding burning body fat whilst maintaining muscle mass is highly favorable. At the same time, fasting secretes growth hormones which will contribute to muscle growth. Adrenaline is also elevated when fasting allowing yourself to enjoy your workout even more.

But when does the body use the protein as an energy source or in other words, when do the muscles break down?

Only after 48 hours of fasting will your muscles be broken down for energy consumption. This is however not the case when following intermittent fasting. Here individuals are advised the maximum fasting period to be no more than 24 hours. What is important though is to avoid a caloric deficit when aiming to increase muscle mass. If you are constantly eating less than if you burn, it will be hard for you to build or maintain your muscle mass. With intermittent fasting, you are more likely to restrict your calories as it might be difficult to consume the same amount of food you used to eat in 3 meals in only 1 or 2 meals. Restricting your calories is good when your goal is to lose body weight, however not favorable when trying to put on additional muscle mass.

Other benefits of intermittent fasting

Other than the brain-related effects, the following benefits can also be seen with intermittent fasting:

  • Prevention of insulin resistance: Insulin resistance is a common problem when the body secretes insulin all the time due to sugary meals consumed too often. Type 2 diabetes is the consequence. Intermittent fasting decreases insulin secretion as in the fasting period, sugar (in the form of carbohydrates) is not consumed. At the same time, your eating frequency will decrease creating fewer peaks of insulin production.
  • Less weight and belly fat: As said before, your body will use body fat as the energy source as soon as the glycogen stores (stored carbohydrates) are used up. This happens usually 12 hours after the last meal. With a normal diet you therefore never reach a fat burning state (lipolysis). Intermittent fasting allows your body to enter this fat burning state every day even if you only fast for 16 hours which will, therefore, reduce your body fat. At the same time, hormones which facilitate fat loss will increase in fasting periods too.
  • Enhances lifespan: Certain genes are turned on when doing intermittent fasting promoting longevity.

My experiences with intermittent fasting

I follow the 16/8 method, in which I fast for 16 hours with a feeding window of 8 hours. I skip breakfast prolonging the fast and have my first meal around 2 pm. I found myself being more focused in the morning and also more productive as my body is not occupied with digestive processes. At the same, especially at the beginning, I still experience a bit of hunger a few hours before I break the fast. I realized coffee to be a good way to blunt the hunger and at the same time enhance concentration.  Coming to the eating window, I find it a lot easier to prepare the meals as I have to cook and clean up less. What I realized though is how difficult it can be to eat all the needed calories within just a short period of time. Especially when trying to put on muscle mass, tracking your calories is an absolute necessity or you risk constant under eating. I definitely recommend trying this diet, always keeping in mind going to a nutritionist. I am only 2 weeks in now but I can see my body change already. I have a lower body fat percentage with the same amount of muscle mass which was my goal. Also I find it easier to control my hunger in the fasting periods.

Have you tried this diet? Has it worked for you? Let us know in the comments below!

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