It’s Not “Just Stress”: The Science Behind What’s Really Happening in Your Body (and How to Take Back Control)

21 May

The Misunderstood Power of Stress

We've all heard it — “You’re just stressed. You need to relax.” And yet, it’s often said with a dismissive tone, as if stress were a mere nuisance rather than a central player in our overall health. But what if we told you that chronic stress isn't just a mental burden — it's a full-body, system-altering force that fundamentally changes the terrain of your health? And what if the idea of the "terrain" — your body's internal environment — was the real key to understanding why some people thrive and others break down in the same circumstances?

Because here’s what exhausted, high-functioning parents are hearing on repeat:

From the doctor: “Your blood work looks fine. It’s probably just stress.”
From their partner: “You just need to calm down.”
From their teen: “You’re being extra — just chill.”
From their boss: “You’ve got to get it together.”

What sounds like everyday advice is actually a chorus of dismissal — and it misses the bigger picture. Stress isn’t just stress. It's not in your head. It’s in your hormones, your gut, your immune system, your sleep, your energy, your patience, your everything.

Understanding how stress reshapes our internal landscape is critical if we want to protect ourselves from chronic disease, infections, fatigue, and burnout. This isn’t just about managing stress for “wellness.” It’s about recognising stress as a core disruptor of the systems that keep you resilient, balanced, and alive.

The Terrain Theory: A Forgotten Foundation of Health

To understand how stress dismantles our health, we must begin with a different view of disease — one that has existed for centuries but was overshadowed by germ theory.

Antoine Béchamp, a French biologist and contemporary of Louis Pasteur, proposed terrain theory. He believed that germs are not the root cause of disease — the state of the body, or terrain, is. In other words, whether pathogens take hold or not depends largely on the condition of your internal environment.

Pasteur, famous for his work on germ theory, argued that microbes cause disease, period. But near the end of his life, Pasteur reportedly admitted, “The microbe is nothing. The terrain is everything.”

The terrain encompasses everything from the pH of your tissues, the integrity of your gut lining, your hormone balance, immune function, micronutrient levels, mitochondrial health, and yes, your stress levels.

When your terrain is strong, it resists infection and imbalance. When it's weakened by chronic stress, poor sleep, overwork, toxic exposure, and nutrient depletion, it becomes fertile ground for illness, fatigue, and chronic dysfunction.

What Is Stress? A Physiological and Hormonal Breakdown

Stress is not merely an emotion; it's a complex physiological response involving multiple systems in the body. While we often talk about stress as a negative force, it's important to understand that not all stress is bad. In fact, acute stress can be your superpower — if you learn how to use it.

Acute vs. Chronic Stress

Acute stress is short-term and can be incredibly beneficial. It sharpens focus, boosts motivation, and primes your body and brain to perform under pressure. When managed well, acute stress becomes a tool for growth and achievement — a secret weapon you can learn to harness. I explore this idea in depth in my blog, From Pressure to Power: Mastering the Stress That Fuels Your Success, where I share how to train your body and mind to turn acute stress into fuel for success.
Chronic stress, on the other hand, is a different story. It’s prolonged, often low-grade and relentless, and it gradually wears down your systems. Over time, it can suppress immunity, disrupt digestion, alter hormones, and set the stage for burnout and chronic disease.

Nervous System Shifts: Sympathetic vs. Parasympathetic

Your autonomic nervous system has two branches that work in tandem:

The sympathetic nervous system activates the stress response, increasing heart rate, dilating pupils, raising blood pressure, and diverting blood flow to muscles. It’s designed for immediate action.
The parasympathetic nervous system does the opposite — it promotes “rest and digest”, allowing for recovery, digestion, repair, and immune function.

Under chronic stress, your body remains stuck in sympathetic overdrive, and the consequences ripple through nearly every system:

Systems that are prioritised in stress mode:

Brain (heightened alertness)
Muscles (prepped for movement or defence)
Cardiovascular system (increased heart rate and blood pressure)
Liver (glucose release for immediate energy)

Systems that are deprioritised or suppressed:

Digestive system (slows or halts digestion)
Immune system (temporarily suppressed)
Reproductive system (libido and fertility take a back seat)
Repair and detoxification (reduced cellular repair and elimination)
Long-term memory and emotional regulation (impaired by prolonged cortisol exposure)

This is why people under chronic stress often struggle with gut issues, frequent colds, hormone imbalances, fatigue, and even brain fog or emotional reactivity — because the body is stuck in survival mode, and the systems that keep you healthy over time are running on empty.

How Stress Alters the Terrain

When the body is exposed to chronic stress, the systems that were deprioritised in the momentary stress response begin to deteriorate over time. What was once an adaptive survival strategy becomes a source of dysfunction, gradually reshaping your internal terrain and making you more vulnerable to illness, fatigue, and burnout.

Let’s explore exactly how this happens.

Immune Dysregulation

Prolonged cortisol exposure suppresses immune activity, weakening your body’s natural defences. Over time, this makes you more susceptible to infections, slows down wound healing, and can contribute to chronic inflammation and autoimmune issues.

Digestive Suppression and Microbiome Disruption

Your gut takes a direct hit under stress. Blood flow and enzyme production decrease, while stress hormones shift the balance of gut bacteria, reducing beneficial microbes and allowing harmful ones to thrive. Chronic stress also increases intestinal permeability (“leaky gut”), which can trigger food sensitivities, bloating, and systemic inflammation.

Hormonal Imbalance and Mitochondrial Dysfunction

Stress throws your hormones out of sync, disrupting thyroid function, reproductive hormones, and insulin sensitivity. At the same time, it impairs mitochondrial function, the energy factories of your cells, leading to persistent fatigue, brain fog, and slower recovery from exertion or illness.

When Stress Is Productive, and When It’s Devastating

Hormesis vs. Chronic Load

Hormesis refers to the beneficial effects of mild stressors, like exercise, which can enhance resilience.
Chronic stress, however, overwhelms the body's adaptive capacity, leading to detrimental health effects.

Stress as a Signal vs. Stress as a Threat

Acute stress serves as a signal for the body to respond to immediate challenges. Chronic stress, perceived as a constant threat, keeps the body in a prolonged state of alert, disrupting normal functions.

“You’re Too Stressed”: Why Doctors Are Often Right

While it may feel dismissive, attributing health issues to stress often has a solid physiological basis. Chronic stress isn’t just “in your head” — it can manifest through a wide range of "unexplained" symptoms, including persistent fatigue, digestive issues, hormonal fluctuations, and mood disturbances.

In some cases, stress may even contribute to the onset or worsening of autoimmune conditions, such as Hashimoto’s thyroiditis, rheumatoid arthritis, or lupus. The reason? Chronic stress dysregulates immune function, increasing systemic inflammation and impairing the body’s ability to distinguish between self and non-self. While it’s not the sole cause, stress is often the spark that lights the fuse in those already genetically predisposed.

When Stress Doesn’t Feel Like Stress

Many people say, “I’m not stressed.” And mentally, they might not feel overwhelmed. But stress isn’t just a conscious experience — it's also a physiological state. The body may be under pressure even when the mind is distracted or numbed. In fact, some of the habits we turn to for “relaxation” may actually be quietly stressing the system, altering hormone balance, impairing recovery, and disrupting the internal terrain.

Let’s look more closely at these hidden stressors:

Scrolling: Mindless scrolling can seem like downtime, but it overstimulates the brain with constant novelty, hijacks dopamine pathways, and can increase anxiety and mental fatigue. It also exposes you to blue light, which disrupts melatonin production when scrolling at night, impairing sleep quality, one of your body’s main tools for repair.
Alcohol: A glass of wine may take the edge off emotionally, but alcohol is a nervous system depressant that interferes with deep sleep, blood sugar regulation, and liver detoxification. The body treats it like a toxin, which means it’s a physiological stressor, even if it “feels relaxing” in the moment.
Skipping Exercise: While rest days are essential, completely avoiding movement reduces the circulation of mood-boosting neurotransmitters like serotonin and dopamine, weakens mitochondrial function, and prevents the healthy stress signal that builds resilience. Without it, you may feel sluggish and more reactive to stress.
Sacrificing Sleep for “Me Time”: Staying up late to catch a break from your day might feel like self-care, but sleep debt increases cortisol, decreases emotional regulation, and impairs immune function. It’s a costly trade-off that leaves the body less equipped to handle daily demands.
Processed Comfort Foods and Stimulants: Sugar and caffeine give short bursts of energy or comfort, but they destabilise blood sugar, deplete micronutrients, and strain the adrenal system over time. The result? Crashes, cravings, irritability, and more stress are layered into the body’s terrain.

How a Damaged Terrain Makes Us Vulnerable

When the body is constantly managing hidden stressors — poor sleep, overstimulation, processed food, or lack of movement — the terrain quietly weakens. These small, everyday habits chip away at foundational systems like the gut, the immune system, and the mitochondria, creating an internal environment where imbalance and dysfunction can thrive.

A compromised terrain doesn't just lead to fatigue or low mood — it lowers your resilience to external threats:

Susceptibility to Pathogens: When immune function is suppressed due to chronic stress and systemic inflammation, the body is less able to recognise and respond effectively to bacteria, viruses, and even internal threats like abnormal cell growth. You might find yourself catching colds more often, recovering slowly, or dealing with lingering symptoms from minor illnesses.
Variable Responses to the Same Exposure: Ever wonder why one person gets sick while another doesn't — even in the same household or office? It often comes down to terrain. A well-regulated body with a balanced nervous system and strong cellular health can buffer the impact of daily exposures. In contrast, a stressed, depleted body may tip into illness more easily, even if the trigger appears minor.

This isn’t about living in a sterile bubble — it’s about building a strong internal environment that can handle life’s challenges without breaking down.

Rebuilding the Terrain: What Real Resilience Looks Like

If chronic stress can wear down your terrain, then resilience isn’t just about being “tough”—it’s about creating an internal environment that supports recovery, balance, and vitality over time. This is the true essence of health: not avoiding every challenge, but being able to face them without falling apart. Rebuilding the terrain means intentionally restoring the systems that stress depletes.

Regulating Stress

To shift from survival mode back into balance, we need to actively regulate our stress response. This doesn’t just mean “relaxing” — it means training your nervous system to move fluidly between action and recovery.

Practices like mindful breathing, meditation, or journaling can reduce sympathetic dominance.
Regular physical activity, especially rhythmic movement like walking, swimming, or strength training, helps burn off excess stress hormones while stimulating calming neurochemicals. Exercise increases cortisol and adrenaline as an acute response, but in a healthy, purposeful context, it actually trains the nervous system to shift between stress and recovery more effectively. This adaptability is key to long-term resilience. Additionally, shared movement experiences — like walking with a friend or attending a group class — can release oxytocin, enhancing feelings of connection and safety. Movement also boosts endorphins, dopamine, and myokines, all of which support emotional resilience, cognitive function, and overall health.
Even short daily pauses — stepping outside, stretching, or practising stillness — can rewire your brain’s stress pathways over time.

Real Recovery Habits

True recovery isn’t about escaping stress; it’s about creating space for repair. This includes both physical and emotional restoration.

Sleep is one of the most powerful tools for healing the terrain. Deep sleep supports hormone regulation, immune repair, and detoxification.
Restorative activities like time in nature, unstructured play with your kids, or quiet time away from screens allow your system to reset.
Strong social connections can buffer the effects of stress by activating oxytocin and the parasympathetic nervous system. A single warm conversation can be more healing than a whole bottle of supplements.

Supporting Detox and Immunity

When your body isn’t overloaded, it can do what it was designed to do: cleanse, regulate, and defend itself.

Eat a nutrient-dense, whole-food diet that supports your gut, liver, and immune system. Think colourful vegetables, high-quality protein, healthy fats, and fermented foods.
Stay well-hydrated to support lymphatic flow and cellular detox.
Reduce your toxic load by limiting alcohol, smoking, highly processed foods and being mindful of your environment (indoor air quality, plastics, etc.).

Conclusion: A Call to Take Stress Seriously

Understanding the profound impact of stress on our internal terrain underscores the importance of proactive stress management. Stress is not just a mental or emotional issue — it reshapes our biology, alters our immunity, and determines how resilient or vulnerable we are to chronic illness.

But here’s the empowering part: we’re not powerless. As I explore in my blog, From Pressure to Power: Mastering the Stress That Fuels Your Success, stress doesn’t have to be the enemy. In fact, when understood and harnessed wisely, stress can become a tool for growth, clarity, and performance.

By recognising and addressing the ways stress alters our physiology — and by making intentional changes in how we move, rest, eat, and think — we can rebuild a stronger, more adaptive terrain. The goal isn’t to eliminate stress, but to build the internal resilience to thrive through it.

This is your invitation to turn awareness into action. Not tomorrow — today.

Dimitrina Fileva