Why the mind affects the body: anxiety, somatization, and the nervous system that turns emotion into physical pain

Every emotion you don't process, your body turns into a symptom. If you've ever felt your heart race without having run, a knot in your stomach before a meeting, or simply lost your appetite for days without being ill, you've surely heard —or thought— one of these lines: “It's just stress, it's nothing,” “Relax, it's all in your head,” or “It'll pass, no need to dwell on it.”

We've been taught to separate mind from body as if they were two tenants living on different floors who never cross paths in the elevator. As if whatever you feel emotionally stayed locked away in some abstract corner of your head, without touching anything else.

There's a problem with that separation: it doesn't exist. Your nervous system doesn't distinguish between a physical threat —a car braking hard in front of you— and an emotional or psychological one —a message from your boss at eleven at night. Both activate exactly the same circuit. And that circuit doesn't stay in your head: it travels down to your heart, your gut, your muscles, and your immune system. We call this biological process, by which psychological distress shows up in physiology, somatization.

If you want to understand why the Mind pillar is just as non-negotiable as the Movement pillar → within NEXUS's philosophy, set aside the idea of “willpower” or “just push through it” for a moment. What happens to your body when your mind is overloaded is pure physiology —and it's much easier to understand than you think.

Why does your heart race in a meeting that isn't dangerous? Think of your autonomic nervous system as a car dashboard with two pedals, not one.

The problem isn't having the accelerator —you need it, it's saved your life more than once without you noticing. The problem is never letting go of it. A phone notification, an unresolved argument, a never-ending to-do list: to your nervous system, all of that can sound like a low-volume fire alarm that never quite switches off. And an accelerator pressed fourteen hours a day, every day, wears the engine down —literally.

This isn't just a figure of speech: a meta-analysis published in Psychiatry Investigation, which pooled 37 studies on heart rate variability (HRV) —the most direct physiological marker of the balance between the sympathetic and parasympathetic systems— found that low parasympathetic activity is the most consistent finding associated with sustained psychological stress.[1] In other words: when you live stressed, your body measurably loses its ability to brake.

Why does anxiety kill your appetite or send you into non-stop eating? Have you ever felt “butterflies in your stomach” before something important? That's not just a figure of speech: it's the direct manifestation of the gut-brain axis.

Your digestive system has its own neural circuit —the enteric nervous system, with more than 500 million neurons— and it's connected bidirectionally to your brain through the vagus nerve.[2] When you experience anxiety, that pathway sends the alarm signal downward; and when your microbiota or digestion is disrupted, the signal travels upward, feeding the state of mental alertness.

That's why stress doesn't produce a single, predictable psychosomatic symptom. In some people it shuts down hunger signals entirely —the body interprets that “this isn't the time to digest, it's time to survive” and redirects energy to the muscular system. In others, the opposite happens: stress triggers food-seeking, especially foods dense in sugar and fat, as a fast —if not particularly effective long-term— way of calming the nervous system.

The evidence backs both patterns: a meta-analysis published in Health Psychology Review, which combined 54 studies with more than 119,000 participants, found that stress is, on average, associated with higher consumption of ultra-processed foods and a reduction in nutritious food intake —but with individual variability so high across studies that the authors themselves insist there's no single “correct” stress response, but several forms of regulation.[3]

For a long time, depression was treated as if it were just a mood or a chemical deficit. Current neuroscientific evidence also describes it as a measurable, low-grade inflammatory state in the blood.[4]

When the body keeps inflammatory markers like C-reactive protein or interleukin-6 activated for weeks, those same molecules interfere with the neurotransmitters that regulate mood, motivation, and appetite. It's not that you “lack motivation”: your immune system, without you deciding it, redirects resources toward what it interprets as a sustained threat. It works the same way a phone enters power-saving mode and shuts down non-essential functions: appetite, concentration, and the urge to socialize all drop.

A 2024 review published in BJPsych Open, which analyzed 44 studies on inflammatory biomarkers in depression, found that elevated C-reactive protein levels consistently correlate with appetite loss and difficulty concentrating, while interleukin-6 is especially linked to anhedonia —the inability to feel pleasure.[4]

The same physical symptom —a twinge in the chest, a tension headache— can feel radically different depending on the interpretation your mind builds around it.

If you interpret tachycardia as “I'm having a heart attack,” the sympathetic nervous system receives a second alarm signal —this time generated by the thought itself— and the somatization cycle feeds itself. It's exactly the same dynamic we cover in our piece on what pain is and how the brain processes it →: the brain doesn't react only to what's happening in the tissue, it reacts to what it interprets is happening.

A large part of your nervous system is regulated through other people, a biological phenomenon known as co-regulation —the same territory we'll be developing further down the line in the Journal's Social Relationships pillar.

A conversation with someone you trust can measurably lower your heart rate and cortisol levels. Prolonged isolation, on the other hand, keeps the alarm system more active than necessary. It's no coincidence that unwanted loneliness is one of the most consistent risk factors for both anxiety and cardiovascular disease.

It's essential to tell everyday acute stress —activating and even useful in short doses— apart from a sustained state of somatization that starts limiting your quality of life.

Some physical and emotional signs that call for a health professional's assessment (psychologist, psychiatrist, or your GP):

As the Health Psychology Review meta-analysis with more than 119,000 participants confirmed, there's no single “correct” way to express stress: some people lose their appetite, some overeat, some develop insomnia, and some experience constant drowsiness. That variability isn't a flaw on your part —it's precise information about how your nervous system is managing the threat.

Asking for professional support isn't the last resort reserved for “when you truly can't take it anymore”: it follows the exact same logic as seeing a physiotherapist for persistent joint pain →, before it turns into a chronic problem. At NEXUS, we don't separate mental health from physical health.

At NEXUS, we don't believe mental health is an isolated compartment, or that “toughing it out” is a physiological virtue. We believe in accurately interpreting what your nervous system has been trying to tell you through your body.

If you've had a racing heart, a closed-off stomach, or drained energy for a while, the answer is almost never “think positive” and keep going. The answer is giving your nervous system biological certainty that the danger has passed: breathing differently, moving, connecting with someone, and —when needed— asking for professional help without waiting for a crisis.

Remind your body that your mind and it aren't separate tenants, but the same house.