TV and internet advertisements pitching products promising to reduce cortisol would have you believe that this hormone can magically create belly fat out of thin air. Fortunately, the science behind cortisol’s effect on the body has been largely twisted and taken out of context—it isn’t exactly the evil fat loss sabotaging, muscle eating hormone that it’s been made out to be.
To understand the truth about cortisol, you’ll need to know why it’s made and what exactly it does.
Cortisol actually has a very important role in the body, acting to increase the creation of new sugar in the liver when carb or calorie intake is low. It does this by creating glucose from certain amino acids, and this typically happens in the post-workout period after you’ve burned through sugar in the blood.
Because cortisol helps to liberate fuel when you need it, it’s actually a good thing to see a short-term rise in cortisol. This can help you work harder in the gym and improve your performance once you burn through your immediate energy stores. This is why cortisol is usually elevated after an intense workout, and why training-induced increases in muscle mass are actually associated with a rise in cortisol. If cortisol doesn’t go up after training, you either went into your workout extremely well fed, or you didn’t work hard enough to burn through glycogen stores (stored carbs around your muscle).
Where things get problematic is when cortisol stays high over the long term...
In certain conditions or scenarios where cortisol is chronically high (Cushing's Disease), we see a loss in muscle mass, as proteins are leached from muscle to be turned into glucose. People who suffer from this, as well as those who’ve been on corticosteroids for a long time, often have a skinny fat appearance along with muscle wasting.
Additionally, having a high-stress life (job and life stress, poor sleep, etc.) tends to create an environment where cortisol is constantly elevated throughout the day, instead of following its normal fluctuations. When cortisol levels are behaving as they should, they’ll be high in the morning and low at night, and will temporarily rise to liberate more energy in a state of stress, exercise, and fasting.
Prolonged and abnormally high cortisol levels usually only occur as a consequence of severe health issues and in response to extreme conditions that most people won’t face.
If you’re concerned about high cortisol levels following a workout, simply eat some carbohydrates. Doing this will suppress cortisol release and bring hormone levels back down to their pre-training state.
The idea that cortisol will make you fat and melt your muscle is one of those gimmicky fitness myths spun out of a theory that only partially makes sense.