Intermittent Fasting

Intermittent fasting is a simple approach to dieting that might just be the easiest and healthiest way of not only burning fat, but also helping improve overall health. On this article, I’ll show the research on how to control insulin production through intermittent fasting, to help you lose fat and keep your muscles.

What is intermittent fasting

Fasting is a practice as old as humanity itself, practiced by millions of people worldwide for different reasons. All the major religions on the planet recommend fasting and, as medical research advances, more and more medical practitioners are publicly recognizing the several advantages that fasting can bring to our modern lifestyle. I am quite sure that everyone in this planet knows that fasting is simply not eating for a determined period. There is, however, a little more to it.

Intermittent fasting is not a new form of calorie restriction diet. Intermittent fasting is a pattern of eating. It’s a way of scheduling your meals so that you get the most out of them. Intermittent fasting doesn’t change what you eat, it changes when you eat. It is one of the simplest and most ignored strategies available for a complete body re-composition.

The actor Chris Pratt in a before and after body transformation photo. from fat to muscular
Lose the fat, save the galaxy

How hard it is to fast?

As any five-year-old kid knows and we somehow forget during adulthood, the easiest way of loosing fat is not to eat. It is the simplest dietary change in the planet, the easiest to implement and very possibly the most effective change to achieve the body you want.

Intermittent fasting does not require you to change what you eat, only to discipline the time of when you eat. There is no need for extra-complicated cooking, with strange and expensive ingredients. While the first few days may be a challenge for those who spend the whole day munching, after a very short time your body will adapt to it, specially if you do your meals always around the same time. I guarantee you that, if you do not cheat on your fasting, all the cravings for food you may feel throughout the day will completely vanish as if they never existed after a very short while.

IF, fat loss and insulin control

The first and most visible benefit of Intermittent fasting is fat burning. Even if eating the same amount of calories daily, intermittent fasting will cause your body to burn fat, simply because it has nothing else to burn. And it is all related to insulin. Here comes the science!

Insulin is the major hormone that regulates the absorption of nutrients from food. Insulin is secreted whenever you eat, and that is an extremely important piece of information. Also, Insulin is the hormone who “gives the order” for the body to store energy in the form of fat through the process of lipogenesis (1).

During normal-day operations, the human body is constantly spending energy, be it to move, think, or simply to stay warm. Whenever we eat, some of the food energy is stored in an easy-to-burn form: glucose. Although glucose is an easily accessible form of energy, the body cannot store much of it. So, instead of “throwing away” all that useful energy that cannot be stored in the form of glucose, insulin gives the order of transforming that energy into triglycerides – fat.

As the day progresses and we spend our stocks of glucose, our insulin levels drop. When insulin levels drop, the order to store energy in fat form ceases, and instead our bodies begin to burn stored fat for energy.

In summary: You eat, your body releases insulin that sends the energy to be stored into fat. You don’t eat, your insulin levels drop, giving the signal for your body to burn the energy stored into fat (2). That is not new science, we know this for almost seventy years.

Let me repeat this in another way so that this information sinks: Every time you eat – A.K.A. consume calories, you are actively preventing your body from burning fat. The more you eat, the larger the amount of insulin released and the longer it takes to go down to fat burning levels. That is not even considering insulin resistance, a topic that we will discuss below.

By now, you already understood just how fundamental is the insulin process for burning fat.

The conventional approach to weight loss and why it doesn’t work

The classic method of losing weight prescribed by everyone who doesn’t understand how important is insulin is a diet with a restriction of calories combined with an increase in exercise.

The problem with this method is that the human body is very well designed for adaptation, and therefore will easily adapt to the more restrictive diet by lowering its metabolism, making the calorie restriction desired effect cease to function. Also, most of the time this kind of diet prescribes several small meals a day, which keeps your insulin levels high, preventing your body to burn fat effectively.

First, as there is no constant intake of food, there is no such insulin triggers during fasting. Second, metabolism does not slow down with intermittent fasting, simply because that is the way the human body was made to work (3). Imagine you live in prehistoric times, having to hunt or gather to eat. After two days without eating, your metabolism does not make you sluggish, diminishing the chances of finding food. On the contrary, your metabolism enters overdrive, filling you with energy so you actually can find food and avoid starvation. The biggest proof of this metabolism overdrive caused by fasting is that we, as a species, are still around (3).

As for the people who still think that they will lose muscle mass with fasting, there were several studies on the area, proving that losing muscle mass due to fasting simply does not happen (4).

Caveman defends family from bear attack
Honey, tell this brute to come back later, I’m too weak from my 16 hour fast

This is another example of form following function, proven by science. The human body evolved for many thousands of years, but humanity only had access to ready sources of food, with the ability to actually eat everyday, in the last few centuries. For the first several thousand years, scarcity was common and eating didn’t happen everyday. Most – if not all – food came from hunting and gathering, activities that rely heavily on muscle mass. Even after the development of agriculture, another labor intensive activity, food was not necessarily available everyday. If we actually lost muscle mass for not eating during short periods of time, we would gather less food, we would sow less land. We would gradually become weaker until we, as a species, would starve to death, long before leaving our proverbial cave.

Extra key benefits of intermittent fasting

It makes your day simpler and it’s easier than dieting

We like cooking. That is one of the main reasons we made this blog. But even enjoying our time in the kitchen, it is impossible not to realize that we spend a lot of time in it, time that could be used elsewhere. One less meal preparation per day means not having to plan or shop for it, which means more free time and a simpler day.

Also, as far as calorie restriction diets go, it is simply impossible to keep them for long periods without feeling miserable. Worst, your body will adapt to eating less calories everyday and, the moment you return to eat the same amount as before, the blubber you lost will come back with a vengeance (6).

Intermittent fasting helps you live longer

It is amazing just how much information was discovered and then forgotten or simply ignored.

We know since 1945 that caloric restriction prolongs the lifespan of mice (5). In 2006, the study was expanded from caloric restriction to alternate day intermittent fasting, with even more significant results (7), leading to even longer lifespans. This is readily available information that in a perfect world should be taught in school.

Intermittent fasting promotes autophagy

Autophagy is the body’s natural detox: it’s the way of cleansing itself of its faulty and dead cells when there’s no longer enough energy to sustain them. It is a regulated, orderly process to degrade and recycle cellular components first described in 1962 by the Nobel prize winning scientist Christian de Duve, who also coined its name.

It is easy to understand the importance of autophagy: just imagine that you never take away the trash from your home and you will get a very accurate picture.

The consequences of accumulating old junky proteins all over the place can be seen in two main conditions: Alzheimer’s Disease (8), in which the brain abnormally accumulates proteins in the wrong places, and cancer (9), which is the abnormal growth and reproduction of defective cells.

Autophagy happens all the time in the human body… except when we eat. Glucose, insulin (or decreased glucagon) and protein ingestion will turn off this self-cleaning process. And it doesn’t take much. Even a small amount of amino acid (leucine) could stop autophagy cold (10). So the process of autophagy is unique to fasting – something not found in simple caloric restriction or dieting.

Currently there are several studies evaluating intermittent fasting, autophagy and their relation in treatments against several diseases, including cancer. For now, we will have to wait for the results, but this is a very promising field.

Insulin resistance and diabetes type 2

Full disclaimer: I’m a med school dropout, not a medical practitioner. When in doubt, always consult your doctor. Now that this is out of the way, please indulge me as I gather the scientific facts we have already discussed in this post.

First, every time you eat, your body releases insulin. Every. Single. Tiny. Snack.

Second, carbohydrates release more insulin than proteins, which in turn release more insulin than fats. Remember this when you eat a candy bar or drink a soda in the middle of the day.

Third, the human body is highly adaptable.

These simple three facts will inescapably lead to how the body develops insulin resistance: Whenever someone spends the whole day munching – specially carbs such as sweets (add cereal bars to that) and sodas – this person’s body is kept swimming in insulin. When the body invariably adapts to this high hormonal level – which incidentally will keep the body from burning fats, – this person develops insulin resistance.

Insulin resistance happens when cells stop responding correctly to insulin and present difficulties in using blood glucose for energy, regardless of how abundant this glucose might be. To make up for it, the pancreas makes more insulin, and this solves the problem for a short while. However, as time goes by, the pancreas isn’t able to keep up and the blood sugar levels rise, leading to obesity, high blood pressure, high cholesterol, and the dreaded type 2 diabetes.

That is how the intermittent fasting, combined with a keto diet, can actually prevent diabetes type 2: Fasting – and NOT snacking – allows the body’s insulin levels to drop between meals, just as nature intended. When your body does not have high levels of insulin, it cannot become resistant to it. No insulin resistance, no diabetes. Simple, right?

Remember: Avoid diabetes before it sets on, because after the body is sick, intermittent fasting alone is very unlikely to cure it.

Just as an extra incentive to avoid insulin resistance: common complications of insulin resistance include a higher risk of heart attack, stroke, kidney disease, eye problems, cancer and Alzheimer’s disease. Oh, and obesity. Insulin resistance, although easily preventable, is the root cause of most chronic diseases.

How to start intermittent fasting

To put it bluntly, stop eating. It doesn’t get easier than that.

There are several different time frames to do your fasting, from measly twelve hours to alternate day fasting. For the last year I have been following the pattern of sixteen by eight, which means that I fast for sixteen hours and eat during the remaining eight hours.

By all means that does not mean that I spend eight hours eating! I usually eat only two fulfilling meals, one around noon and the other around seven p.m. It is a very comfortable schedule, and very easy to get adapted to.

A clock face showing how the 16:8 intermittent fasting window works

Do sleeping hours count toward the fast?

Yes, they do. As I said before, I eat my last meal of the day around seven p.m. and my first meal on the next day around noon. That counts for sixteen to seventeen hours of fasting, and to fast while sleeping is a breeze.

Can I eat or drink while intermittent fasting?

This should be self-explanatory: while fasting, you do not eat nor drink anything with calories. No juices, no milk, no food, no sweet beverages, no shakes and no BCAAs. If it has calories, you are not fasting.

Water, plain black coffee and tea don’t have any calories (unless you put sugar or milk on them), so they are perfectly fine to drink. It’s important to stay hydrated during fasting.

Diet “calorie-free” drinks like flavored waters and diet soda should be avoided, as there are some evidence to show that some artificial sweeteners cause an insulin response, which would then blunt your ability to burn fat and contradict the point of being in a fasted state, but research in that area is still in its infancy.

BCAAs and fasting

BCAA or branched-chain amino acids combine to form protein. If you consume them, you are consuming calories, meaning that you are no longer fasting.

That said, if you are going to train on a fasted state, BCAAs are a powerful source of energy for the muscles, and their benefits for your workout potentially outweigh breaking your fast early. (For more information read our post about Fasted Cardio)

There are a couple of exceptions to this. Amino acids that aren’t proteinogenic such as beta-alanine, betaine and D-aspartic acid can be safely consumed without breaking your fast. Another two supplements that can be consumed without breaking your fast are L-carnitine and creatine.

Eating at last! How do I break my fast?

So you finished your first day of intermittent fasting and are wondering if is there anything that you should be eating as you break the fast. Well, the answer is no. You can break your fast eating whatever you want to eat, as long as it is a healthy choice. Personally, I enjoy a hearty dose of protein when breaking my fast and, being on a keto lifestyle, I tell you that there is absolutely nothing wrong with bacon and eggs with some keto waffles or keto muffins.

You will be eating the same number of calories and macros per day, just with a different meal schedule. The whole idea is that you should eat healthily, meaning not too much and not too little. If you have any difficulties in measuring the amount of food, just count your macronutrients. It is very simple and effective.

Intermittent fasting is easy, healthy and helps your body to burn fat while keeping your muscles. Try it, you won’t regret it.

1 Kersten S. Mechanisms of nutritional and hormonal regulation of lipogenesis. 

2 Christensen DP, Dahllöf M, Lundh M, et al. Histone deacetylase (HDAC) inhibition as a novel treatment for diabetes mellitus. 

3 Redman LM, Ravussin E. Caloric restriction in humans: impact on physiological, psychological, and behavioral outcomes. 

4 Bhutani S, Klempel MC, Berger RA, Varady KA. Improvements in coronary heart disease risk indicators by alternate-day fasting involve adipose tissue modulations. 

5 Anton J. Carlson, Frederick Hoelzel, Apparent Prolongation of the Life Span of Rats by Intermittent Fasting: One Figure

6 Klempel MC, Bhutani S, Fitzgibbon M, Freels S, Varady KA. Dietary and physical activity adaptations to alternate day modified fasting: implications for optimal weight loss. 

7 James B. Johnson, Donald R. Laub, Sujit John The effect on health of alternate day calorie restriction: Eating less and more than needed on alternate days prolongs life.

8 Cataldo AM, Hamilton DJ, Barnett JL, Paskevich PA, Nixon RA. Properties of the endosomal-lysosomal system in the human central nervous system: disturbances mark most neurons in populations at risk to degenerate in Alzheimer’s disease. 

9 Hippert MM, O’Toole PS, Thorburn A. Autophagy in cancer: good, bad, or both?

10 Glynn EL, Fry CS, Drummond MJ, et al. Excess leucine intake enhances muscle anabolic signaling but not net protein anabolism in young men and women. 


  1. Vocês sentiram halito cetônico com o jejum? Sei que existe toda função bioquimica da liberação dos corpos cetônicos, mas não sei se existe uma maneira que não aconteça ou alguma maneira de driblar ele. Vocês tem alguma dica?

  2. Olá Eduarda! Eu pessoalmente não senti, mas perguntei ao Daniel se ele lembra e ele disse que definitivamente sentiu, vindo de mim haha Realmente é algo natural, e que vai embora assim que seu corpo se adaptar a esta nova forma de utilizar a energia. Eu sugiro beber mais água, pois ajuda a expelir o excesso de cetonas através da urina. De resto, manter um “distanciamento social” até o corpo estar adaptado funciona também 😉

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