Introduction
Stress is truly ubiquitous in this modern day and age. The list of reasons are endless – It could be deadlines at work or just the fact that you really don’t enjoy your job. It could be that you have a new child, or maybe you’re going through some issues with your interpersonal relationships. Your traffic-filled commute in the morning isn’t helping, either. Regardless, we’re all under stress, some people much more so than others.
What most people don’t realize is that stress has much farther reaching consequences than just making you feel overwhelmed or anxious. Everything from cognitive health to cardiovascular health to physical health – Chronic stress negatively affects all of it.
Stress and the HPA Axis
Let’s zoom out and start with a bit of general education on the stress and the HPA axis. The HPA axis is one of the primary hormonal axis’ that regulates our stress response through a hormone called cortisol. There are others, such as the catecholamines (epinephrine and norepinephrine), but we’ll focus on cortisol and the HPA axis first.
Whenever we’re under stress, the hypothalamus in the brain releases a compound called CRH that gets sent to another area of the brain; the pituitary. This gland send out a hormone called ACTH, which then communicates to our adrenals to make cortisol. Cortisol gets released and has its effects on the body.
Acute bursts of cortisol are not always a bad thing. It wakes us up in the morning, it helps give us energy during exercise, and its anti-inflammatory. However, when cortisol is chronically high, as in chronic stress, we see an entire slew of negative effects happening all across the body.
Going through chronically elevated cortisol’s effects on the entire body would be a several day masterclass, so in this post, we’re going to focus on all things metabolic health, meaning insulin sensitivity, nutrient partitioning, which ultimately translates to how stress can hamper your efforts to undergo body recomposition – Lose fat and gain muscle.
We’re going to take it organ by organ, showing the effects of chronic stress on the brain, fat tissue, skeletal muscle, and liver. Let’s dive in.
Chronic Stress and your Metabolic Health
The Brain
The brain is the ultimate command control center. Although we have hunger hormones and satiety hormones that result in being hungry or feeling full, all of these act through changing activation of certain sets of neurons in the brain.
The main set of neurons in the brain that stimulates hunger are called Agrp/NPY neurons. Ghrelin, our primary hunger hormone, acts on these to make us hungry.
However, cortisol also increases the activation of NPY neurons, which then drives appetite and cravings as well as decreases daily energy expenditure. This activation of NPY neurons by cortisol also stimulates the pancreas to release more insulin, which, over time, can negatively affect our insulin sensitivity.
The first effect of chronic stress in the brain as far as metabolic health goes, summarized, is that it’s going to screw up your hunger and satiety signals, facilitating cravings and making it harder to stick to your diet. It also has the effect of increasing insulin secretion, which is not necessarily a good thing if it’s chronic.
The Fat Tissue (Adipose)
When most people think about fat tissue, they think of the type of fat that most people want to lose; the fat that’s right underneath our skin that hides all of our muscle definition and curves.
Another type of fat that’s significantly worse for our health is visceral fat; this is fat that’s stored around the organs. Visceral abdominal fat is particularly heinous; fat that we store around the organs in our abdominal cavity. Chronic stress, and therefore chronically elevated cortisol, shunts fat storage to visceral fat.
Have you ever seen someone that doesn’t exactly look overweight, but has a gut? Maybe their gut is also particularly hard to the touch, like a bowling ball. This is probably a good amount of visceral fat being stored in the abdominal cavity.
Visceral fat continuously spits out fatty acids into the bloodstream and also straight to the liver through the portal vein. If the amount of fatty acids being spit out overwhelms the speed at which other tissues are taking it up and burning it, then we get significantly more insulin resistance.
Fat can potentially build up in the liver, resulting in non-alcoholic fatty liver disease, and also hampers the livers insulin sensitivity. This increase in fat and triglycerides can also induce muscular insulin resistance as well.
The Muscle
Our muscle tissue is basically our sink for glucose; up to 70% of our glucose disposal from the bloodstream is due to our muscle. However, chronic stress directly decreases glucose uptake into the muscle, leading to higher blood sugar.
Since the glucose isn’t getting taken up by the muscle, it has to go somewhere. This decrease in glucose uptake leads glucose back to the liver to be turned into fatty acids. The liver attempts to package these into triglycerides and spits them out into circulation and the increase in systemic triglycerides can also cause lipid buildup in muscle, causing further insulin resistance.
Not only that, but cortisol highly increases muscle protein breakdown. Whenever we’re trying to build muscle, we always have to consider the balance of muscle protein breakdown vs. muscle protein synthesis, and chronic stress is going to shunt this further down the side of breaking down muscle.
The Liver
The liver is an extremely important organ that performs hundreds of functions for our body. If you’ve been keeping track so far, there’s many aspects of chronic stress that can cause fat build up in the liver.
We have fatty acids coming from visceral fat tissue, but then also fatty acids being created from glucose within the liver. This doesn’t even take into account the fatty acids we’re eating, which could further exacerbate things.
This will not only destroy liver insulin sensitivity, but hamper many of its other functions as well, causing significant oxidative stress and inflammation.
Chronic stress and elevated cortisol also drives gluconeogenesis, or the creation of glucose. In normal physiology when we’re not stressed, gluconeogenesis is generally occurring after we haven’t eaten for a while, which helps keep our blood sugar at good levels.
However, even if we’ve just eaten a meal with glucose, if our cortisol is very high and we’re quite stressed, we could be creating glucose inappropriately, adding to the glucose load from our meal. Let’s go ahead and summarize and integrate
Integration
Let’s piece this altogether starting with visceral fat. Chronic stress is going to cause more visceral fat storage, which is continually spitting fatty acids into the bloodstream and to the liver.
The muscle is trying to take up these excess fatty acids and triglycerides, causing muscular insulin resistance. The products of muscle protein breakdown fueled by cortisol travel back to the liver to create glucose through gluconeogenesis.
Since we’re insulin resistant, the glucose thats being created in the liver and also coming in from our meals isn’t being taken up as readily by the muscle, so it goes back to the liver to be turned into fat to be stored.
Non-alcoholic fatty liver is mainly driven by the balance of “Fat in” versus “fat out” or the fat coming into the liver vs. the fat being exported, and in this situation, we have a lot of sources that elevate the “fat in” portion. Fat coming from visceral fat, from our meals, from the creation of fat from glucose, and potentially from our fat tissue under the skin, depending on how overweight we are.
All the while, the brain is causing us to be hungrier and crave more hyperpalatable foods, in addition to increasing insulin secretion by the pancreas.
Even if you are able to maintain a caloric deficit while highly stressed, your muscle recovery will be significantly reduced because of the increased muscle protein breakdown, and you’ll be in a body that really wants to hang onto its fat stores and use its muscle breakdown for energy while in a deficit.
On top of that, many chronically stressed people suffer from insomnia, so if we put that in the mix too, we have all sorts of hormonal aberrations that can occur that exacerbate all of this.
The Solution
Stress is an inevitable part of daily life, but we can manage it through many techniques that include meditation, breathwork, art, music, walks in nature, and just scheduling fun things you enjoy.
The name of the game is parasympathetic activation and getting your head out of rumination mode (worrying about the future, past, or even immediate situations) and into the moment of exactly what you’re doing.
I have a podcast all about stress management techniques, which is episode 224 in the Sam Miller Science podcast feed, so please check that out for further information.
References
Geer et al. Mechanisms of Glucocorticoid-Induced Insulin Resistance. Journal of endocrinology and metabolism. REVIEW ARTICLE| VOLUME 43, ISSUE 1, P75-102, MARCH 01, 2014. DOI:https://doi.org/10.1016/j.ecl.2013.10.005
