Misconceptions About the Ketogenic Diet and Sport

This article is the first article in a series about the role of the ketogenic diet in a sporty lifestyle. This first article kicks off this series with a number of misconceptions, myths and persistent fallen pseudoscience, better known as ‘bro-science’.

The definition of bro science? It is a collective term for misconceptions and ideas of dubious scientific credibility, passed on by word-of-mouth by lay people and accepted as factual truths.

It is a well-known saying in the land of fitness: “abs are made in the kitchen”.

This sounds like a piece of pure, unadulterated bro-science, but the purpose of this one-liner is of course that your eating pattern is extremely important for the composition of your body. And this is 100% true! How many calories you get and from which food you get your calories determines how your body looks and how fit you feel.

How you coordinate your training and nutrition ultimately determines what results you achieve.

Regarding the ketogenic diet in combination with training, there are also misconceptions that can be confusing. In this article we will deal with the various misconceptions about ketogenic diet and sport.

Misconception 1: Carbohydrates are needed to grow muscles

The above misconception is somewhat understandable. The role of carbohydrates in the development of mass cannot be denied. But to what extent does one consume a lot of carbohydrates by developing muscle mass?

Carbohydrates stimulate the release of the hormone insulin to the blood. The mechanism works as follows: you eat carbohydrates (sugars), then the blood sugar rises and your pancreas releases insulin to the blood to ensure that the sugars in the blood can be absorbed by body cells.

Insulin functions as an anabolic hormone . It therefore ensures that your body can create mass. The only problem with this is that the insulin does not care what type of mass is produced.

The only thing insulin is interested in is stabilizing your sugar level. Insulin doesn’t matter that you develop fatty tissue as a result.

All carbohydrates that cannot be used directly as an energy source are stored using insulin as:

  • Muscle glycogen
  • Liver glycogen
  • Fatty tissue

Glucose is stored by the body in the form of glycogen as an energy reserve for the muscles.

Since your body can only store a limited amount of glycogen in the muscles and in the liver, some of the carbohydrates you consume will be stored as fat. So you can grow Faster mass with carbohydrates, but part of it is FAT. And that is not the type of mass you are looking for!

The ketogenic diet offers a way to grow mass that is perhaps slower than if you follow a carbohydrate-rich diet, but it is then FAT-FREE muscle mass .

There are three conditions that you must meet during a ketogenic diet to be able to create this fat-free muscle mass:

  1. You will have to consume a surplus of calories.
  2. You will need to consume enough protein.
  3. You will have to train in the right ways.

We will discuss these ‘ muscle culture conditions’ separately.

Surplus calories

This golden rule that applies to any diet that wants to grow mass is that it is a requirement that you eat more calories than you consume.

Because if you sit under your calorie requirement in terms of nutrition, then your body will have to compensate for the deficit by using energy reserves. For that, it will also break down muscle mass, and that’s not what you want!

If you want to grow mass during the ketogenic diet, then you will need to ensure that you get more calories than you consume. Fortunately, fat is a high-calorie energy source and you can quickly create a surplus by increasing your fat intake.

However, there is a way to be able to grow muscle mass even in the event of a calorie deficit!

But it is a process that is not easy . The ketogenic diet is fortunately the diet par excellence where it is possible!

The key lies with the fat adaptation that takes place when you have been in ketosis long enough. At that moment your body is able to quickly and efficiently convert fat reserves into fuel for the muscles.

If the body is NOT adapted enough to fat as a fuel, then in the case of an energy shortage it will also start to break down muscles , so that it can make glucose from the proteins (gluconeogenesis).

But for someone who is fully fat-adapted , this does not happen so quickly, provided that the energy shortage is not too large (500 kcal is a good guide number). The energy shortage that occurs during intensive workouts is then supplemented from the body’s fat reserves.

At that moment you burn fat while at the same time you grow muscle mass.

This is, incidentally, a process that must be well thought out . If you have too large an energy deficit, where you sit well below your calorie requirement, you can run the risk that your muscles will ‘burn up’.

A good guideline to keep in mind is to sit around 500 kcal below your daily requirement with your diet.

If you are fat-absorbed, your body will supplement the 500 kcal deficiency by breaking down fat reserves. During a week your body will therefore have to supplement 3500 kcal from fat reserves.

Fat has a calorific value of 9 kcal. So you will burn around 400 grams (3500/9) of fat a week, while building muscle.

Enough protein consumption

Proteins are crucial for creating muscle mass. Proteins provide your body with the necessary building blocks (amino acids).

The following protein sources are suitable during a ketogenic diet:

  • Eggs
  • Red meat
  • Fish
  • Poultry
  • Full fat dairy

If you try to grow muscle mass or improve your performance during the ketogenic diet, it is recommended that you consume around 2.2 grams of protein per kilo of lean body mass .

The reason you take the fat-free mass as a starting point is because muscle mass is maintained by means of proteins. If you take the total weight as a starting point, then the body composition of the person is not taken into account.

For example, Person A can be very trained and muscular and weigh 80 pounds, while Person B also weighs 80 pounds, but is overweight and low in muscle mass.

Despite the fact that both people weigh 80 kilos, Person A has a much greater need for proteins because his muscle mass invites this to be maintained. Fatty tissue needs less protein.

Now you think maybe? Lean body mass? What is that? And how do I calculate it?

You can calculate this mass by subtracting your fat percentage from your body weight. An example:

Suppose you weigh 88 kilograms and your fat percentage is 18.3%. Then you use the following formula:

88 x 0.183 = 16.104

The above calculation therefore indicates that you have 16.1 kilograms of body fat. You then deduct this from your total body weight:

88 – 16.1 = 71.9

Your fat-free mass is therefore 71.9 kilograms .

You now know that you need to consume approximately 71.9 x 2.2 grams of protein to grow muscle mass. This amounts to around 158 grams of protein per day .

When you sit far below this daily recommended amount of protein with your meals, you do not provide your body with enough building blocks to actually allow muscle growth.

Calculate macros

You can then use this number of grams of protein to calculate your intake of fats and carbohydrates, ie your macronutrients. How can you do this? We will give you a calculation example.

In the ketogenic diet, most of your daily calories come from fat. About 70-75%. Proteins around 20-25%. Carbohydrates make up 5% of your daily calories.

You can then calculate the daily composition of your macronutrients. Earlier you calculated what your protein requirement is. According to the example in this text, that was 158 grams.

Proteins have a calorific value of 4 kcal . In total, you therefore receive 632 kcal of protein. These 632 kcal make up 25% of your daily calories according to the ketogenic distribution of macronutrients, so a fourth part.

This means that your daily calorie requirement is around 4 x 632 kcal, ie 2528 kcal.

You can then calculate how many fats you can consume. Fats have a calorific value of 9 kcal. About 70% of your daily amount of calories should come from fats.

This means that 0.7 x 2528 = 1770 kcal of calories should come from fat. You then divide this number by 9 (calorific value of 1 gram of fat) and you arrive at approximately 197 grams of fat.

You calculate the number of carbohydrates in the same way: 0.05 x 2528 = 126 kcal. Divide this by 4 (calorific value of 1 gram of carbohydrates) and you will end up with 32 grams.

It is completely understandable if you do not feel like a rocket scientist with a calculator must calculate how much fat, protein and carbohydrates you can eat in a day .

That is why we have the solution for you: the  Keto Calculator . 

With this calculator you can precisely match your macronutrients to the goals you have in mind with the ketogenic diet!

Train in the right way

When you have just started the ketogenic diet then you will be in a transition phase where you can feel less energetic. Your performance capacity can also be affected by this. This is no more than normal .

It is a phenomenon known as the Keto Flu. 

The transition from glycolysis (the use of glucose as a fuel) to ketosis (the use of fat as a fuel) takes some time. If after a few weeks your body has adjusted to the use of fat as fuel, it is able to efficiently fuel your muscles.

So you can very well practice strength sports during the ketogenic diet and thus grow lean muscle mass!

Growing muscle mass requires a good training schedule where you gradually train harder. In this way you create stronger muscles, resulting in an increase in muscle mass.

Want to know more about the ketogenic diet in combination with strength sports? We have written an in-depth article about it: The Ketogenic Diet and Strength Sports .

Misconception 2: Meal planning is important because you have to eat proteins at the right times

From the fitness and supplement industry, there are various reasons why it is promoted that the timing and consumption of proteins is enormously important.

The main reason, of course, is that companies want to sell more supplements and protein powders to athletes. For this reason concepts such as ‘ anabolic window ‘ have been created.

The theory behind the anabolic window is that your body is in an anabolic state after training. That is why this period would be essential for muscle recovery and growth. The duration of this supposed anabolic window? Up to an hour.

This fine example of bro-science without any scientific substantiation comes from a blog article from one of the largest online supplement stores in the Netherlands.

Not surprisingly, this blog article links several times to the various ‘fast-absorbing hydrolyzate protein powders’ that the online store has for sale. And of course the fast-absorbing carbohydrates should not be missing either! Because of course you don’t want to leave the ‘anabolic window’ untapped … Because, according to bro-science, the anabolic window is a FACT.

It is all the more praiseworthy that another major international player in the supplement market simply plays an ‘open card’ . In their scientifically supported blog article , they state that the Anabolic Window is nonsense. So, bro science!

The following quotes are from the blog article:

“A study was done in which a group of people received proteins immediately before and soon after the training and in which a group of people received proteins in the morning and in the evening. The difference in strength and body composition between the two groups after 10 weeks was examined here. The results from this study were clear. There was no significant difference between the two groups. Both groups had progressed just as quickly in strength and body composition. (1)  This research shows that the Anabolic Window, as they claim, does not exist. “

“From yet another study, we looked at the difference in strength and body composition between two groups after 16 weeks. One group who received a high-protein meal immediately after training and one group who received a high-protein meal at least 2 hours after training. After 16 weeks the subjects were again looked at strength and body composition. It turned out that there was no significant difference between the two groups. (2) This research also shows that the Anabolic Window, as they claim, does not exist. “

We could not have put it better ourselves. The timing of your proteins is therefore not very important . The most important thing is that you consume your protein during the day so that your body can use it when needed.

Your body is able to retain the broken down proteins as amino acids in the small intestine, and then release them when the body needs them (3) .

As long as your total protein consumption is sufficient, you will therefore always have building materials ready to enable muscle growth and recovery.

What, however, a point of attention during the ketogenic diet is that you do not TOO MUCH protein would consume at one time, because it can get out of ketosis.

There is a chance that your body will produce the many proteins it receives through the process of gluconeogenesis glucose.

How do you prevent you from eating too much protein in one go? By dividing the amount of protein over different eating moments. For example, if your goal is to eat 160 grams of protein in a day, then it is better to divide this into four eating moments at which you consume 40 grams.

Again, planning these ” protein consumption moments ” has nothing to do with the absorption of proteins. Your body is perfectly capable of processing and ‘buffering ‘ all the proteins you consume as amino acids in the small intestine for later use.

However, this is about maintaining your ketosis, so you do that by spreading protein consumption over several eating moments. This way you prevent your body from possibly producing glucose from proteins.

Misconception 3: Sporting achievements lead under the ketogenic diet.

In general, people assume that sporting performance diminishes during the ketogenic diet. But this is NOT TRUE in most cases .

After all, it is not the case that sporting performance by definition deteriorates during the ketogenic diet. Various studies have been done on the performance of athletes who were in ketosis and these paint a different picture.

One study investigated the aerobic endurance of trained cyclists who had followed a ketogenic diet for four weeks. The results showed that their endurance unaffected was (4) .

In another study, professional gymnasts were subjected to a ketogenic diet consisting of green (leaf) vegetables, olive oil, and proteins from fish and meat.

So these were athletes who professionally perform exercises where different muscle groups are heavily loaded. Weight loss and fat loss were observed in this group, but no significant reduction in muscle strength and muscle mass (5) .

As mentioned, in most cases the negative effect of the ketogenic diet on physical performance is not proven .

It may of course be that during the transition period from a carbohydrate-rich to a low-carbohydrate diet the body still has to adapt to the use of fat as a fuel.

But after this adjustment period your body knows how to use fat optimally as an energy source for strength and endurance .

Another opportunity where ketosis can cause a reduction in performance is with exercises that require explosive force. In such cases, it may help to replenish glycogen stores .

You can do this in two ways. By means of a targeted ketogenic diet (TKD) , in which you consume approximately 25 to 50 grams of carbohydrates just before the start of your sports session.

A second way is to follow a cyclic ketogenic diet (CKD) , where you follow a strict ketogenic diet for 5-6 days and use 1-2 days to supplement glycogen stores. On these days you will therefore need a carbohydrate-rich diet.

When you do intensive sports such as football, hockey, handball, and Crossfit, or have heavy strength training sessions, such variants of the ketogenic diet can offer a solution to maintain the explosive power that your muscles can get from glycogen.


In this article we have discussed various misconceptions about the ketogenic diet.

Misconceptions about the timing of your meals, the muscle-building potential of the ketogenic diet and about the sporting performance during the ketogenic diet have been refuted based on scientific research.

We will once again summarize the various findings:

  • If you eat enough protein during the ketogenic diet then it is quite possible to build muscle mass . You are therefore not dependent on carbohydrates to grow muscle mass! You should consume approximately 2.2 grams of protein per kilo of fat-free body weight.
  • Your daily total protein intake is much more important than the timing of meals. Ideas such as the ‘Anabolic Window’ are not scientifically substantiated and seem to be mainly maintained by parties who want to sell supplements.
  • It is important not to consume too much protein in one go because this can bring you out of ketosis . Your body will be able to break down the abundance of proteins into glucose through the gluconeogenesis process. So try to spread protein consumption throughout the day.
  • Match your calorie intake to your goals . Are you planning to grow muscle mass? Then you have to ensure that you get more calories than you consume. If you want to lose weight then you will have to create a calorie deficit, in which you consume more than you consume.
  • Train well . To stimulate muscle growth you will have to take the right approach during your sports session. By training with weights you can give your muscle groups a strong boost to become stronger. You can gradually increase the intensity and intensity of the training.
  • Use targeted carbohydrate consumption during variants of the ketogenic diet such as the Targeted Ketogenic Diet (KTD) or the Cyclic Ketogenic Diet (CKD) to supplement your glycogen stores for high-intensity sports sessions.

With the above tips you can ensure that you get even more benefit from the combination of the ketogenic diet and a sporty lifestyle.

In addition to this article about the misconceptions surrounding the ketogenic diet and sports, there are also articles in this series that go deeper into the ketogenic diet and strength sports , and the ketogenic diet and endurance sports .

Fan of everything health and fitness related. My mission is to share my knowledge and experience with as many people as possible and help them to find their ideal path to perfect health.

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