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The best cortisol article ever What cortisol really does and how to control it

Der beste Kortisolartikel aller Zeiten Was Kortisol wirklich tut und wie man es kontrolliert

Cortisol is like a bogeyman. To discourage exercisers from doing extreme things, we tell them that cortisol will eat up their gains. While this statement has a kernel of truth, it doesn't represent the whole picture.

Believe it or not, there is not a single hormone in the body whose job is to destroy the body. Cortisol has many key functions, but sometimes this hormone causes some collateral damage when it comes to looking good naked. Let's take a closer look at this hormone.

The functions of cortisol

I refer to cortisol as the 'readiness hormone' rather than calling it the stress hormone. Its main function is to ensure that you are ready to deal with any potentially threatening situation.

  1. It increases alertness, focus, energy and drive. It does this by increasing your adrenaline levels. Cortisol increases levels and activity of an enzyme called phenylethanolamine N-methyltransferase (PNMT). This enzyme converts noradrenaline into adrenaline. Through this action, cortisol increases adrenaline levels, which has a direct impact on your state of consciousness.
  2. Cortisol increases the heart's beating rate and contraction force. This supports the transportation of oxygen to the muscles and the removal of metabolic waste products. This also occurs via an increase in adrenaline levels
  3. It increases the contractile strength of the muscles. This is the third effect of increased adrenaline levels.
  4. It mobilizes stored energy. It does this to prevent you from running out of energy when you are fighting or running away from a sabre-toothed tiger. This is an unselective process, which means that all potential energy sources are broken up and mobilized by cortisol: Muscle and liver glycogen, fatty acids from body fat and amino acids from muscle tissue.
  5. It helps to maintain stable blood sugar levels. It increases blood sugar when it is too low (together with glucagon and growth hormones).
  6. It inhibits the immune system. This is done to ensure that you have more resources to fight the enemy. Just like in Star Trek, when the captain says "Divert all available energy to shields!" during a battle, the body does the same when cortisol tells it that it is facing an enemy. During times of battle, the immune system is inhibited and as soon as cortisol levels drop again, it is fully ramped up again to repair the damage of the battle.

Note: You can't separate cortisol from any of its functions. When it is elevated, all of these 6 things will happen.

So cortisol is a necessary and quite important hormone. It's essential to increase cortisol levels when you're fighting a tiger, setting a new personal best in the deadlift or trying to gain possession of the ball in football. However, if cortisol levels are elevated for too long, this can have negative effects.

Let's take a look at how this affects our muscle growth, fat loss, recovery and wellbeing.

Cortisol and muscle growth

When cortisol levels are chronically elevated, this can affect your muscle growth through several mechanisms:

  1. Cortisol directly increases muscle breakdown. The amount of muscle you build depends on the difference between protein breakdown (catabolism) and protein synthesis (anabolism). If you increase protein breakdown (which is what cortisol does), then it will be much harder to build muscle.
  2. Cortisol reduces the uptake of nutrients by the muscles. This makes it harder to get amino acids and glucose into the muscles to build muscle tissue and replenish muscle glycogen stores.
  3. It increases myostatin levels. Myostatin is a myokine (protein) that is secreted by the muscles and inhibits muscle growth. The more myostatin your body produces, the less muscle you can build. By increasing myostatin levels, chronically elevated cortisol levels will limit your growth potential.
  4. Over time, cortisol can lower testosterone levels. Testosterone and cortisol are both made from pregnenolone. If your body produces too much cortisol, it can reduce the amount of pregnenolone available to make testosterone.
  5. It slows down muscle repair. The repair of damaged muscle tissue after a training session depends heavily on your immune system. Chronically elevated cortisol levels weaken the immune system, making muscle repair less efficient.

After a training session, the rate of protein synthesis is increased for 24 to 36 hours (although only significantly for 24 to 30 hours). This is the window of time you have to repair the muscle damage and build new muscle tissue. If your immune system is weakened, your body may need this entire period to simply repair the damage caused. This means that you don't have time to build muscle during this window. This is a dilemma that can make your muscle building very slow.

Cortisol and fat loss

If you are familiar with the body composition analysis approach (biosignature, bioprint, metabolic analysis), then you know that the system claims that excess cortisol leads to fat storage in the abdominal area.

If you remember what the functions of cortisol are, then you may see a contradiction here. Ultimately, one of the functions of cortisol is to mobilize stored energy (including fat) - not store it.

More specifically, cortisol is a fat loss hormone - at least when it is released in a pulsatile manner. But that doesn't mean that chronically elevated cortisol levels can't make it harder to lose fat. While a short-term increase in cortisol levels is involved in fat loss, a chronic increase in the levels of this hormone can make the fat loss process more difficult.

How? In 2 ways...

1. cortisol can reduce the conversion of T4 to T3

T3 is the thyroid hormone that has the biggest impact on your metabolic rate. When T3 levels are higher, your metabolic rate increases and you burn more calories on a daily basis.

If T3 levels fall, your metabolic rate will also fall. T4, on the other hand, does not have such a great influence on your metabolic rate. Your body produces T4 and converts it to T3 in the amount it deems safe for your body's survival.

However, if you are chronically short of energy, your body will slow down the conversion of T4 to T3, causing your metabolic rate to drop. When cortisol levels were chronically elevated during our evolution, it meant that we were unable to find food and as a result cortisol levels had to be kept high to keep blood sugar levels stable and mobilize stored energy.

The body adapted to this by reducing T3 levels to conserve energy. Back then, we needed this adaptation. Today, chronically elevated cortisol levels can be triggered by many stressors and even if we are not in a state of energy deficiency, the chronic cortisol problem will still lead to a reduced conversion of T4 to T3.

2. chronically elevated cortisol levels can lead to insulin resistance

Cortisol increases blood sugar levels. When we were cavemen, this wasn't a big problem as cortisol levels only rose when we had to be physically active (fight or run away) or when we lacked food. So we used the glucose released to fuel the body.

However, if your blood sugar levels rise when you are inactive, they will remain elevated, leading to hyperglycemia. Your body doesn't want this and it will release insulin to bring blood sugar levels back into the normal range. It's all good, isn't it? Not really.

When cortisol levels are chronically elevated, this means that it continually raises blood sugar levels, which in turn leads to regular insulin secretion. This in turn can lead to insulin resistance.

Both a reduced metabolic rate and insulin resistance can make it harder to lose fat. No, they do not override the laws of thermodynamics. Achieving a calorie deficit is still the most important thing when it comes to fat loss. However, if cortisol lowers the metabolic rate, this means that it will be harder to achieve a calorie deficit (and easier to achieve a calorie surplus).

You should keep in mind that insulin alone will not make you fat. It can only store the nutrients you eat - it does not generate new nutrients. If you are in a calorie deficit and have high insulin levels, you will not gain fat.

However, insulin can make it harder to mobilize stored fat. As long as insulin is elevated above baseline, it will be harder to mobilize fat efficiently. If you are insulin resistant, this means that your cells are not responding well to insulin. As a result, you need to produce more insulin to accomplish the same task. When you produce more insulin, it takes longer for insulin levels to fall again. If they stay elevated longer, then you spend more time in a state where fat mobilization is less efficient.

Cortisol is not a fat-building hormone, but chronic elevation of cortisol levels can make it harder to lose fat over time.

Cortisol and regeneration

Cortisol will have a negative impact on your recovery if it is chronically elevated.

  1. Cortisol leads to increased adrenaline levels. This is great before a training session, but not so good when you want to go to bed.
  2. It inhibits your growth hormone production. Oddly enough, in vitro studies (studies done in test tubes) have shown that cortisol can increase growth hormone levels, but in vivo studies (studies done with live humans) have shown that cortisol decreases growth hormone production. If your cortisol levels are elevated at night - when your normal growth hormone production is at its highest - then this will seriously affect your recovery process and progress.
  3. It reduces glycogen storage, which is an important part of your post-workout recovery.
  4. It can slow down your muscle repair. This goes back to how cortisol affects muscle growth...see above.

Cortisol and wellbeing

Chronically elevated cortisol levels affect wellbeing - especially mental wellbeing. However, it's a little more complicated than that because cortisol affects neurotransmitters. The key point to remember in this context is that cortisol leads to an increase in adrenaline levels. When cortisol is chronically elevated, this leads to the following:

  1. Cortisol can lead to a depletion of noradrenaline stores. Adrenaline is produced from noradrenaline. If too much noradrenaline is converted into adrenaline, this can lead to a depletion of noradrenaline stores. The latter leads to reduced focus, low blood pressure and potentially depression and anxiety.
  2. It can lead to a depletion of dopamine reserves. Noradrenaline is produced from dopamine. If there is an overproduction of adrenaline, then you risk depleting dopamine stores. Symptoms of low dopamine levels include a lack of motivation, a lack of pleasure, depression and listlessness.
  3. It can desensitize the beta-adrenergic receptors. If your body produces too much adrenaline - and especially if this happens around the clock, as is the case with chronically elevated cortisol levels - then you risk desensitizing your beta-adrenergic receptors. The body does not like being stimulated by adrenaline around the clock as it is not safe. Chronically elevated adrenaline levels can lead to high blood pressure, which can have serious consequences for the cardiovascular system. Desensitization of the receptors is a protective mechanism against this. Your body therefore stops reacting to adrenaline (or the reaction is weaker). This leads to reduced energy, lack of motivation, lack of drive, lower performance, laziness and depression.
  4. It can increase the production and transmission of glutamate (1). Although this can make your working memory more effective in a stressful situation, an excessive increase in glutamate levels can lead to mood swings, depression and excessive emotions, as well as taking everything personally. Not to mention that excessive glutamate can be neurotoxic.

The effects of cortisol are even more far-reaching than this, but that's the gist of it. The bottom line? Short bursts of cortisol at the right time (in the morning and when you exercise) are very useful, but chronic elevation can quickly become problematic if you want to look and feel your best.

How to keep your cortisol levels under control

I'm going to forgo the voodoo recommendations like "make your peace with the universe". Instead, I'll look at training, nutrition and supplement strategies.


There are three main components of training that affect cortisol release. To control these, you should avoid combining high levels of 2 (or all 3) of these cortisol-increasing factors.

  1. Training volume: The more work you do, the more energy you need. The more energy you need, the more cortisol you will release to mobilize the necessary energy sources.
  2. Necessary effort: The higher you go on the rate of perceived exertion scale, the more likely it is that a set will release a lot of cortisol. If you go to muscle failure, you are more likely to produce a lot of cortisol than if you finish the set 3 to 4 repetitions before reaching muscle failure.
  3. Psychological stress: If a set or exercise is perceived as very stressful, your body will release a lot of cortisol. For example, if you are trying to set a new personal record in squats, this will result in a strong cortisol surge.

Complex exercises such as squats, deadlifts or Olympic weightlifting exercises will also release more cortisol than curls or machine training. Less complexity means less psychological stress. And learning a new exercise can lead to a significant cortisol spike - especially if that exercise is complex.

I've seen people sweat the first time they practiced snatch grip high pulls with the empty bar. The sweating comes from the adrenaline release stimulated by cortisol.

Once you understand this, you can easily put together a strategy to minimize cortisol release. Here are some precautionary steps to follow:

  • If you're using a high volume of work, don't push yourself to your limits on individual sets.
  • Reduce the total volume if you are doing a lot of complex exercises.
  • Avoid going to muscle failure with heavy multi-joint exercises.
  • Keep the volume low when adding very heavy training (in the 92.5%+ of 1RM weight range) to your training program.
  • When you add a new exercise to your program, reduce the total volume until you have mastered the exercise.
  • If you are pushing yourself harder or using a good amount of volume, then you should not change your exercises too often or use too many exercises during a training session.
  • If you combine 2 (or all 3) cortisol increasing factors, then reduce the number of workouts you do per week. Aim for a low training frequency (3 workouts per week) or you will need regular off-load weeks.


One function of cortisol is to maintain stable blood sugar levels. Cortisol increases these when they are too low. One way to minimize cortisol levels is to eat carbohydrates. Or more specifically, to maintain stable blood sugar levels.

This is the reason I don't like very high carbohydrate diets for people who are chronically stressed. Sure, you body can make glucose from amino acids to maintain stable blood sugar levels. And just because you're on a ketogenic diet doesn't mean your body is flooded with cortisol. But eating almost no carbs when you're very active will likely lead to higher cortisol levels.

However, a super high-carb diet is no better, as it can lead to wild swings in blood sugar. But if you eat around 30% of your calories in the form of carbohydrates - ideally from low-glycemic sources - then this will help keep your cortisol levels under control.

I like to eat carbohydrates around my training sessions and in the evening to lower my cortisol (and adrenaline) levels. Remember that you should lower your cortisol levels in the evening to promote sleep and recovery.


There are many strategies you can use to keep cortisol under control. However, you shouldn't wipe out your cortisol levels completely - you need them to train hard. However, you need to be able to lower them again if necessary.

  1. Use the right training supplementation. Easily digestible carbohydrates during exercise can lower cortisol levels by providing energy. When your body has enough carbohydrates available, it doesn't have to mobilize as much stored energy, which means it doesn't have to produce as much cortisol. This is particularly effective if you are following a high volume training plan.
  2. Use vitamin D. This is particularly important during stressful periods. Vitamin D reduces the impact of cortisol on the conversion of noradrenaline to adrenaline. Although this does not directly reduce cortisol levels, it prevents excessive adrenaline production, which can help prevent CNS exhaustion.
  3. Use magnesium after training and in the evening. Magnesium reduces the binding of adrenaline to the adrenergic receptor and can help calm you down while protecting your adrenergic receptors (by keeping them sensitive).
  4. Use Rhodiola in the morning. Rhodiola helps to keep stimulatory and inhibitory neurotransmitters in balance and can also lower cortisol levels.
  5. I like to use glycine after training and in the evening. Glycine is a neurological inhibitor. It reduces the activity of the nervous system when it is overstimulated and also reduces cortisol and adrenaline. Furthermore, glycine increases the amount of circulating serotonin (the feel-good neurotransmitter that also balances mood) and activates mTOR, which will increase protein synthesis after exercise.
  6. Use a good sleep supplement with ingredients like GABA and 5-HTP, which increases serotonin and GABA levels in the brain. These two inhibitory neurotransmitters will allow you to get a more restful sleep, which will allow you to restore a normal cortisol day-night rhythm.


Cortisol is not evil per se. It is needed for survival and to function in stressful situations. However, when cortisol levels are chronically elevated, this hormone can become an enemy to body composition and health. While we don't want to eliminate it completely, it's important to keep levels of this hormone under control in order to achieve your goals, especially if you lead a stressful life.


1 Popoli M, Yan Z, McEwen BS, Sanacora G. The Stressed Synapse: The Impact of Stress and Glucocorticoids on Glutamate Transmission. Nat Rev Neurosci. 2011;13(1):22-37. Published 2011 Nov 30. Doi:10.1038/nrn3138


By Christian Thibaudeau

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