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The true story of Cortisol

Published on 20th Nov 2019 at 13:42 by New You

Believe it or not, there's no hormone in the body whose primary purpose is to destroy the body. Cortisol has many key functions, but sometimes the hormone causes a little collateral damage when it comes to looking and feeling your best. Let's take a closer look.

The Functions of Cortisol

I call cortisol the "readiness hormone" rather than the stress hormone. Its main purpose is to make sure you'll be capable of facing any potentially threatening situation.

  1. It increases wakefulness, focus, energy, and drive. It does so by raising adrenaline. Cortisol increases the level and activity of an enzyme called Phenylethanolamine-N-methyltransferase (PNMT). This enzyme converts noradrenaline into adrenaline. It's through this action that cortisol increases adrenaline, which has a direct impact on your state of mind.
  2. It increases heart contraction strength and rate. This helps with oxygen transport to muscle and the clearance of metabolites. This is also done via the increase in adrenaline.
  3. It increases muscle contraction strength. This is the third impact of increased adrenaline.
  4. It mobilizes stored energy. It does so to keep you from running out of fuel when you're fighting a sabre-toothed tiger or fleeing from it. This is a non-selective process, meaning that all potential energy sources can be broken down and mobilized by cortisol: muscle and liver glycogen, fatty acids from body fat, and amino acids from muscle tissue.
  5. It helps you maintain stable blood sugar levels. It increases blood sugar when it's too low (along with glucagon and growth hormone).
  6. It inhibits the immune system. This happens so you'll have more resources to fight the enemy. Just like in Star Trek when the captain would say, "Divert all available energy to the deflector shields" in the midst of a battle, the body does the same when cortisol tells the body it's facing danger. For example, during times of fight the immune system will be inhibited. As soon as cortisol goes down, it'll be brought back to full force to repair the damage from the battle.

Note: You can't dissociate cortisol from one of its functions. When it's elevated, all of the six things above will happen.

So, cortisol is actually quite necessary. It's essential to have a boost in cortisol when you're squaring or deadlifting. But if it stays elevated for too long it can have some serious negative side effects. Let's take a look at how that affects our muscle density, fat loss, recovery, and well-being.

Cortisol and Muscle

When cortisol becomes chronically elevated it can severely hurt muscle density via several mechanisms:

  1. It 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 cortisol does) it becomes a lot harder to be in a significantly positive balance.
  2. It decreases nutrient uptake by the muscles. This makes it harder to shuttle amino acids to the muscle to build new tissue and restore muscle glycogen stores.
  3. It increases myostatin. Myostatin is a myokine (protein) released by the muscles which limits muscle growth. The more myostatin you produce, the less muscle you can build. By increasing myostatin, chronic cortisol elevation will limit your potential for increasing muscle.
  4. Over time it can decrease testosterone levels. Testosterone and cortisol are both made from pregnenolone. If you overproduce cortisol, you can decrease the amount of available pregnenolone that would otherwise make testosterone. As testosterone drops with age this becomes even more significant from 35 onwards.
  5. It slows muscle tissue repair. Repairing damaged muscle tissue after a training session is heavily dependent on the immune system. Chronic cortisol elevation weakens the immune system making muscle damage repair less efficient.

Note that after a workout, protein synthesis is elevated above baseline for 24-36 hours (although significantly only for 24-30 hours). This is the timeframe you have to repair the damage and add new tissue. If your immune system is weak, it might take you the full duration just to repair the damage you caused. This means you don't have time in that enhanced state to add muscle. It's a predicament that can make muscle growth a very slow process.

Cortisol and Fat Loss

Excess cortisol leads to an increase in abdominal and visceral fat storage.
But if you remember what the functions of cortisol are, you might see a contradiction here. After all, one of the functions of cortisol is to mobilize stored energy (including fat), not store it.

Cortisol is, in fact, a fat loss hormone, at least when produced in a pulsatile manner. But that doesn't mean chronic cortisol can't make it harder to lose fat. While a short-term elevation of cortisol is involved in fat loss, if it becomes chronically elevated it can make the fat loss process harder. How? Two ways...

1 – Cortisol can decrease the conversion of T4 into the active thyroxin T3.

Remember, T3 is the thyroid hormone that has the greatest impact on your metabolic rate. When it's higher, your metabolic rate increases so you burn more calories on a daily basis.

If T3 goes down, so does your metabolic rate. So T4 doesn't have as much of a direct impact. The body produces mostly T4 and converts it into T3 at the level deemed safe for survival by the body.
If you're chronically deprived of energy though, the body will reduce the T4 to T3 conversion, decreasing your metabolic rate. During our evolution, when cortisol was elevated chronically, it meant that we weren't able to find food and that, as a result, cortisol always had to be high to keep blood sugar stable and mobilize stored energy.

It adjusted by reducing T3 levels to lower energy needs. Back then, we needed that adjustment. Sadly, nowadays chronic cortisol elevation can come from many stressors, and even if we aren't in a deprived state, the chronic cortisol issue will still lead to a decreased T4 to T3 conversion.

2 – It can lead to glucose intolerance and insulin resistance.

Cortisol increases blood sugar levels. When we were cavemen and women, that wasn't a big problem because cortisol normally spiked when we had to be physically active (fighting or running away) or were lacking food. So, we'd use the released glucose for energy.

But if blood sugar increases while we're sedentary, it just stays there, leading to hyperglycemia. The body doesn't want that, and it will release insulin to bring blood sugar back down to normal levels. All is fine and good, right? Not really.
If cortisol is chronically elevated it means it'll constantly increase blood sugar levels, which in turn will lead to frequent releases of insulin. That can lead to insulin resistance.

Both a decrease in metabolic rate and insulin resistance can make it harder to lose fat. No, they don't override the laws of thermodynamics. Establishing a caloric deficit is still the most important thing to lose fat. But if cortisol decreases metabolic rate, it means that it'll be harder to create a deficit (and easier to create a surplus).

Keep in mind, insulin alone won't make you fat. It can only store the nutrients you ingest; it doesn't create new nutrients. If you eat in a caloric deficit and have high insulin you won't gain fat.

However, insulin can make it harder to mobilize stored fat. As long as insulin is elevated above baseline, it'll be harder for you to mobilize fat efficiently. When you're insulin resistant, it means that your cells don't respond well to insulin. As a result, you need to produce more to do the same job. If you produce more, it takes longer to bring it back down. If it stays elevated for longer, you spend more time in a state where fat mobilization is less efficient.

Cortisol breaks down muscle - converts it to glucose and makes you glucose intolerant, inhibiting this energy source from making its way to your active cells ( muscle and brain ) whilst driving glucose to be stored as Visceral fat.

Cortisol isn't a fat gain hormone, but its chronic elevation can make it harder to lose fat over time.

Cortisol and Recovery

It'll have a negative impact on your recovery when chronically elevated:

  1. Cortisol leads to elevated adrenaline levels. Great before a workout, but not so much when you want to go to bed.
  2. It inhibits growth hormone production. Oddly enough, in vitro (test tube) studies show that cortisol can increase GH, but in vivo (inside real human bodies) studies show it decreases it. If cortisol is high at night – when you're supposed get your natural GH spike – you'll severely hurt your recovery and progression.
  3. It can decrease muscle glycogen storage. This can be an important part of recovery from training.
  4. It can slow muscle repair. This element of recovery ties back to how it affects muscle growth... see above.

Cortisol and Well-being

Chronically elevated cortisol affects well-being, especially mental well-being. But it's a bit more complex because it impacts neurotransmitters. The key thing to remember is that cortisol leads to an elevation of adrenaline (epinephrine). So when cortisol is chronically elevated...

  1. It can lead to noradrenaline depletion. Adrenaline is made from noradrenaline. If you convert too much noradrenaline into adrenaline you can deplete the former. Noradrenaline depletion leads to a decrease in focus, low blood pressure, and potentially depression and anxiety.
  2. It can lead to dopamine depletion. Noradrenaline itself is made from dopamine. When you over-produce adrenaline you also risk depleting dopamine. Symptoms of low dopamine include lack of motivation, anhedonia (lack of pleasure), depression, and laziness.
  3. It can desensitize beta-adrenergic receptors. If you overproduce adrenaline, especially if you keep producing it around the clock (which happens when cortisol is chronically elevated) you risk desensitizing the beta-adrenergic receptors. The body doesn't want to run on adrenaline all the time; it's not safe. It leads to high blood pressure and can have serious cardiovascular repercussions. Desensitization of the receptors is a protection against that, so you stop responding to your own adrenaline (or the response is much smaller). This leads to low energy, no motivation, self-esteem issues, lower performance, less competitiveness, laziness, and depression.
  4. It can cause increased production and transmission of glutamate (1). While this makes your working memory more effective in a stressful situation, if it leads to excessive glutamate it can cause mood swings, depression, being extremely hard on yourself, being overly emotional, and taking everything personally. Not to mention that excess glutamate is neurotoxic.

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

How to Control Your Cortisol

"Become at peace with the universe." Instead, let's get at the training, nutrition, and sleep strategies.


Train with Intensity but don't overtrain. It's not necessarily about who trains the hardest but it's more about being smart. High volume workouts can leave the body in a sea of cortisol. Get the job done and get out. Spend more time recovering and less time training


Eat regular meals throughout the day and whatever you do don't skip breakfast. Make sure each meal is a balance of protein quality carbs and fats. This mechanism if eating will suppress Cortisol and regulate your insulin levels, enabling you to release more growth hormone during sleep.


Recovery and repair of your cells during sleep is greatly dependent upon the release of GH. Which in turn is dependent upon your eating patterns. GH tells your fat cells to dump some of their cargo, these fatty acids are then transported to your liver where they are burnt as an energy source to produce IGF 1 which is like a fuel injection system directing amino acids into your cells for recovery and building. And lastly get to bed early, staying up late can have a significant effect upon nocturnal Cortisol levels.

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