The Stress That Evolution Has Not Prepared Us For
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For most people an increasing load of chronic stress has become a regular aspect of modern life, regardless if they are aware of it or not. This chronic stress is fueled and amplified by the relentless bombardment with negative news from the media, in particular the internet: the pandemic, catastrophic climate events, a displacement of millions of people resulting in a seemingly uncontrollable refugee crisis, increasing political polarization and a raging war in the middle of Europe are just the most recent examples. On top of that, health books, influencers and social media constantly feed us worrisome and conflicting negative information about our food, dietary habits and our health. This situation has led to what Michael Pollan has rightfully called a national eating disorder epidemic adding anxiety and stress to what normally should be one of our most rewarding times in life, enjoying food with family and friends.
“Our biology has not evolved in an adaptive way to deal with this type of constant … stress exposure”
Our biology has not evolved in an adaptive way to deal with this type of constant and repeated exposure to stress 24 hours a day, 7 days a week. The mismatch between our ancient highly effective biological acute stress response systems which are turned on and off quickly by powerful regulatory mechanisms, and this new form of chronic perturbation of the body’s homeostasis (also referred to as allostatic load) is one of the major factors affecting our health.
“Acute, often life-threatening stress has been part of human life for millions of years…”
Acute, often life-threatening stress has been part of human life for millions of years and there has been enough time in our evolutionary history to perfect our biological stress response systems in a way that has not only kept our species alive through natural disasters, wars, famines and pandemics, but also has resulted in the dominance of planet Earth by our species. There are two such systems in our body: the older immune stress response system and the brain’s acute stress response system, and both are often engaged together.
“The engagement of the brain’s and the immune system response generally occurs in synchrony optimizing the outcome.”
The immune system typically responds to an invasion of pathogens (microbes that are harmful to us) with the initial engagement of the innate immune system, like dendritic cells, leading to the recruitment of different immune cells and powerful tools of the adaptive immune system, as well as the release of both inflammatory and anti-inflammatory cytokines. The balance between these opposing forces determines the severity and duration of the inflammatory response.
The brain also responds to a wide range of perturbations ranging from systemic infections, injuries, psychosocial stressors to worries about potentially harmful events which may occur in the future. Depending on the type and severity of the stressor, and the subjective stress responsiveness of a person, the brain responds with the engagement of the two arms of the stress response system, the sympathetic nervous system and, with increasing severity of the stress, the release of cortisol by the HPA axis. The engagement of the brain’s and the immune system response generally occurs in synchrony optimizing the outcome.
“… the worry about being shot remains a persistent stress for a significant segment of the population”
Our organism responds to any situation that is perceived as a threat to our body’s integrity and homeostasis– in the presence or anticipated to occur in the future –by engaging one or both of these stress response systems. While they have evolved and are optimized to respond to infrequent, but life threatening stressors – the poisonous snake, the wild tiger, the severe injury or the infection, for the majority of people in developed countries, these are no longer the kind of stresses we encounter on a regular basis, even though the worry about being shot remains a persistent stress for a significant segment of the population as highlighted by the ongoing epidemic of high profile police shootings.
For the majority of people today, acute psychological stress occurs in daily situations like being stuck in traffic, being late for an important appointment, or having arguments with your spouse. In general, these stressors are of short duration and we don’t have to worry about their negative effect on our health.
“Our metabolism and the mechanisms controlling our eating behavior are simply not equipped to resist the constant bombardment with commercials promoting unhealthy food…”/span>
Today’s serious perturbation of our body’s balance most often comes in form of chronic stressors associated with modern life: The chronic psychological stress on our minds generated by the relentless daily bombardment with negative news, worries about the future, increasing competition, and number of challenges associated with a lower socioeconomic status (in plain language this means poverty, discrimination, food insecurity, chronic health conditions). Many people are so used to this chronic stress that they may not even be aware of it. It is as if the stress response systems are never turned off, but idling in neutral affecting our general well-being, vitality and energy.
Stress is not limited to psychological stress. There are many perturbations targeted at the gut, including an unhealthy diet, enteric infections, antibiotics, and toxins. So in the same way that a brain-directed stress perturbs the balance first within your brain, spreading to the rest of the brain gut system, the gut-directed stress perturbs first the balance in the complex gut connectome and then spreads to the nervous system.
One important chronic perturbation of our gut and our metabolism is caused by the unhealthy Standard American Diet. Our metabolism and the mechanisms controlling our eating behavior are simply not equipped to resist the constant bombardment with commercials promoting unhealthy food, the grotesque portion sizes in most restaurants and the unhealthy contents of our ultra-processed food, full of saturated fat, sugar, and added chemicals including non-nutritive sweeteners, residues of pesticides in our vegetables and fruits, and microplastic in our seafood.
“The relentless engagement of our stress systems comes at an increasing cost to the health of our bodies and minds.”
Unfortunately, these two type of stressors often occur together, in particular in individuals from lower socioeconomic segments of our society. The relentless engagement of our stress systems comes at an increasing cost to the health of our bodies and minds. Evolution had not foreseen these kind of stressors which we have never experienced as a species. While our stress response systems, the sympathetic nervous system and the HPA axis keep responding in the same way that has been so adaptive for human life, chronic hyperproduction of the stress mediators cortisol and noradrenaline, and chronic systemic engagement of the immune system (the low grade systemic immune system activation everybody is talking about) are responsible for many aspects of our current chronic non-infectious disease epidemic as I have described in detail in The Gut Immune Connection and in the upcoming paperback The Mind Gut Immune Connection.
Not everybody responds to these challenges in the same way: the responsiveness of our neurological and immunological stress system is influenced by genetic factors and is programmed during the first 18 years of life, starting prenatally, in utero, and postnatally, and will determine our lifetime risks for developing these common chronic diseases. This will result in a situation where two people exposed to the same kind and severity of stress will respond in very different ways: one will remain healthy and live to the age of 100 years, the other one developing a chronic disease and dying early. In other words, one person will have a longer health span before chronic disease sets in. Important factors that have been shown to influence the outcomes of living in a chronically stressful world is the quality of social interactions, and the adoption of a eudemonic lifestyle, which means doing meaningful things in life, including doing good for others.
If you want to learn more about this topic, you might also be interested in my upcoming book The Mind-Gut-Immune Connection that you can preorder now, and in the excellent recent book by bestselling author Elissa Epel, PhD, The Stress Prescription which will show you simple techniques how to deal with our current stress dilemma. I will be discussing this topic with Dr. Epel on Tuesday, September 19, 2023 in the evening at a free online event organized by the UCLA Friends of the Semel Institute. See information of how to register for this exciting event at the bottom of this blog.