Stress · Nervous System · Claims graded
“Dysregulated nervous system” has become the explanation for almost everything: fatigue, bloating, anxiety, reacting to supplements, not getting better. Some of what's being said is well supported, some is half-true, and some can't be tested at all. Here is which is which, and what a test can and can't tell you.
Your body runs a stress response that's meant to switch on and off. The sympathetic side mobilises: heart rate up, blood to the muscles, digestion turned down. The parasympathetic side restores: digestion, repair, sleep. Both are always running; what changes is the balance. If the "on" side stays on for weeks and months, through work pressure, poor sleep, illness, grief or money worries, the things that need the "off" side get less attention. Digestion is one of the first.
That much is ordinary physiology, and it's why stress keeps coming up in a practice built around gut and hormone testing. I've written about it before: why calm isn't always the answer, why your stress isn't my stress, and the HPA axis.
The problem isn't the idea. It's what gets built on top of it.
How to read the grades. Strong: consistent results from good trials. Moderate: real trial evidence, but small effects, few trials or some risk of bias. Contested: serious published objections that haven't been answered. None: no evidence either way. Not testable: no result could ever count against it.
Grade: contested.
Polyvagal theory is the framework behind most "safe and social / fight or flight / shutdown" language. It's useful as a metaphor, and many people find it helps them describe how they feel. As physiology, it's in trouble. In 2023, the psychophysiologist Paul Grossman set out why each of its five core premises is either untenable or highly implausible on the available evidence. He also argued that the theory treats one breathing-linked heart-rate measure as if it were "vagal tone", which he calls a category mistake: confusing an approximate index with the thing itself (Grossman 2023).
What that means for you: the feelings are real. The three-state map of the vagus nerve that explains them is not established.
Grade: moderate, small effect.
A 2023 meta-analysis pooled 12 randomised trials (785 adults). Breathwork lowered self-reported stress compared with control conditions, with a small-to-medium effect (g = −0.35), and similar effects on anxiety and low mood. Most trials carried a moderate risk of bias, and the authors themselves warned against "a miscalibration between hype and evidence" (Fincham 2023).
So it helps, modestly, and it's cheap and safe for most people. "Reset" oversells it. More on the practical side in breathwork under pressure.
Grade: moderate, small-to-moderate effect.
Heart rate variability biofeedback, which trains slow breathing against a live readout of your heart rhythm, was reviewed across 58 randomised trials. The effect was small to moderate, no different from other effective treatments, and smaller when compared with an active control rather than no treatment (Lehrer 2020). A reasonable complementary tool, not a cure.
Grade: moderate for the relationship; none for one nervous system "regulating" another.
This is the claim I'd most like to be true, and part of it is. Across 295 studies and more than 30,000 patients in psychotherapy, the strength of the working relationship between client and practitioner correlates with outcome (r = 0.28) (Flückiger 2018). That's a consistent finding, though a correlation isn't proof that the relationship causes the improvement. What the research doesn't show is a practitioner's nervous system physically calming a client's. The honest version is simpler: being listened to, by someone who isn't rushed, matters.
Grade: half true.
No test gives you a validated "dysregulation" score, and anyone selling one should be asked for the validation study. But parts of the stress response can be measured. Cortisol across the day shows how much you're producing and when. The rise in the first 30–45 minutes after waking is a well-studied marker, but only if the samples are timed exactly from waking. An expert consensus warns that sampling errors are common and easily distort it (Stalder 2016). HRV from a wearable tracks a trend over weeks, but it moves with breathing, age, fitness, alcohol and sleep, so it's a personal trend line, not a diagnosis.
Grade: none.
A systematic review of 58 studies found no substantiation for adrenal fatigue as a condition (Cadegiani & Kater 2016). Stress changes cortisol output and rhythm, and that is worth measuring. "Your adrenals are exhausted" is not what the measurements show.
Grade: not testable.
As usually stated, every reaction confirms it and no result could count against it. That doesn't mean a reactive client is imagining things. It means the explanation needs to be specific enough to be checked: which reaction, to what, measured how, and what would we expect to change?
This is where Test, Don't Guess earns its place, and where it has to be careful not to overclaim.
| Tool | What it can show | What it can't |
|---|---|---|
| DUTCH (dried urine, with the waking samples) | Your cortisol pattern and output on the collection day, and how your body is clearing it | A diagnosis of "dysregulation" or "adrenal fatigue"; a pattern from one day can be thrown by a bad night |
| HRV (wearable) | Your own trend over weeks, and what moves it for you | A comparison with other people; a verdict on your "vagal tone" |
| The Metabolic Natures autonomic reading | A structured record of how you've tended to run for years (a questionnaire, not a measurement) | Anything measured. It only changes your plate when the reading is strong, and even then by about two tablespoons of rice a meal |
| Your own record (symptoms against sleep, workload, meals) | Whether your symptoms track a hard week more than your plate | Cause, on its own, but it's the evidence that matters most to you |
The point of testing isn't to put a label on your nervous system. It's to find the things that can be measured, such as a cortisol pattern, a gut finding or a low ferritin, so that stress isn't used to explain everything that's left over.
The alliance evidence is a good reason to protect your own capacity. You can't listen well at 6pm with nothing left. You don't need a theory of nervous-system transmission to justify that. You need a diary that doesn't break you, and the honesty to say when a client's picture is beyond your scope.
If you're an FDN practitioner, the "E" and "S" of D.R.E.S.S. already cover this ground, and they work better when they're specific. What an FDN-P does · FDN in the UK
When it isn't stress. Call 999 for chest pain; palpitations that don't settle or come with chest pain, breathlessness or fainting; collapse or loss of consciousness; sudden confusion; or sudden weakness, a drooping face or slurred speech. If you had palpitations or a faint that has now passed, see your GP urgently or call 111. Panic attacks are real and treatable, but they're a diagnosis to be made, not assumed. If anxiety or low mood is affecting your daily life, your GP is the first step.