Clinical Writing

The Detective Health Blog

Gut health, hormones, blood chemistry, and functional medicine. Evidence-based, clinically grounded, written for people who want to understand what’s actually going on.

Latest articles — 2026
The Book · Test, Don't Guess May 2026
Why I Wrote This Book — And What Changes After You Read It
Five functional tests. 900+ data points. Seven body systems. One method that explains what your GP results never will. Includes video, the five-test framework, and three clinical examples from the blog.
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Resources · Lifestyle · Detox · Gut May 2026
Smart Choices — If You're Going to Do It, Do It Informed
I'm not the health police. Coffee, wine, air quality — how to reduce your exposure load without living like a monk. Practical, testing-informed upgrades for the choices you're making anyway.
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Case Study · Gut · Skin · Metabolic May 2026
Skin, Gut, Blood Sugar, Liver — One Pattern, Four Symptoms
A GP prescribed topical treatment. It failed. The next step was dermatology. A stool test told a different story — dysbiosis, parasites, and a metabolic pattern that connected every symptom to one root-cause picture.
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Supplements · Clinical Reality May 2026
Collagen Is Everywhere. Most of It Is Pointless.
The beauty industry sells collagen as a skin treatment. The wellness industry puts it in coffee. The clinical reality of collagen synthesis is more specific — and the cofactors that make it work are almost never discussed.
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Supplements · Clinical Reality May 2026
More Antioxidants Is Not Always Better.
The antioxidant industry sells protection from oxidative stress. What it doesn't tell you is that reactive oxygen species are signalling molecules the body needs — and that blanket antioxidant supplementation can blunt the very adaptations you're trying to create.
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Technology · Functional Medicine May 2026
Built With AI, Not Built On It.
AI can accelerate functional medicine analysis. It cannot replace 37 years of clinical pattern recognition. Here is what I mean by the difference — and why it matters for the people sitting across the desk from a practitioner using it.
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Gut Health · Nutrition May 2026
Everyone Needs More Fibre. Except When They Don't.
Fibre is critically underconsumed in the modern diet. It is also the category where one-size-fits-all advice causes the most predictable clinical problems. SIBO, low FODMAP, digestive capacity — the nuance the social media posts never mention.
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Blood Testing · Series Part 4 May 2026
The Tests Your Doctor Never Runs
Standard medicine tests for disease. Functional medicine tests for dysfunction — the state that precedes disease by years or decades. Here is what the tests conventional medicine never orders actually reveal.
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Blood Testing · Series Part 3 May 2026
30 Years on a Drug Studied for 8 Weeks
PPIs, statins, metformin, the pill. The medications treating your symptoms may be creating new ones — through nutrient depletion that was predictable, well-documented, and never mentioned at the point of prescription.
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Blood Testing · Series Part 2 May 2026
The Reference Range Problem — Why Normal Isn't Optimal
The reference range on your blood test was designed to identify disease, not optimise health. The gap between those two things is where most chronic symptoms live — and where conventional medicine consistently stops looking.
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Stress · HPA Axis · Life May 2026
Why Zebras Don't Get Ulcers on Sunday Evenings
The Sunday-to-Monday cortisol shift is real and measurable. A functional medicine practitioner watches his own HPA axis fire up on a dog walk in the rain — and writes about what it actually means biologically.
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Exercise & Movement May 2026
We've Been Measuring Exercise All Wrong
We count reps, track miles, log calories. But nobody talks about movement quality — and that's where most people are leaving the biggest gains on the table, and quietly accumulating the most damage.
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Blood Testing May 2026
Your Blood Test Was Wrong Before It Was Analysed
A cup of tea with sugar before the draw. The wrong arm. A non-fasted sample for markers that require fasting. The biggest failures in blood testing happen before the blood reaches the lab.
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✦ Start here
Blood Chemistry May 2026
Iron Deficiency Without Anaemia — The Hidden Epidemic Your GP Will Miss
Your ferritin is 14. Your GP says it’s normal. You’re exhausted, your hair is falling out, and you can’t concentrate. Here’s why optimal ferritin is not the same as normal ferritin — and what to do about it.
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Blood Chemistry May 2026
Your TSH Is Normal. So Why Do You Still Feel Like Your Thyroid Is Broken?
TSH is a pituitary hormone, not a thyroid hormone. A normal TSH tells you the pituitary is happy — it tells you almost nothing about how well your thyroid is actually functioning. Here’s what a full thyroid panel reveals.
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Blood Chemistry June 2026
Five Things Your Blood Test Results Are Telling You — That Nobody Explained
Standard blood tests contain far more information than most people realise. The problem isn’t what’s being measured — it’s the reference ranges, the markers being skipped, and the patterns nobody’s looking for.
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Medication & Nutrition June 2026
The Drug–Nutrient Interactions Your Pharmacist Probably Didn’t Mention
Long-term medication use depletes specific nutrients — often the very nutrients needed to manage the condition the medication is treating. Metformin, statins, PPIs, the contraceptive pill: here’s what each one takes from you.
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Hormones July 2026
Pregnenolone Steal — Why Chronic Stress Wrecks Your Hormones
When the body is under chronic stress, it prioritises cortisol production over every other steroid hormone. The result: low progesterone, low testosterone, thyroid suppression, and a DUTCH panel that looks like hormonal chaos. It isn’t.
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Gut Health July 2026
The GI-MAP Markers Standard Stool Culture Consistently Misses
Standard NHS stool culture identifies roughly 60% of clinically relevant gut pathogens. The GI-MAP uses quantitative PCR — DNA detection — with sensitivity exceeding 95%. Here’s what the difference means for your symptoms.
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Archive
Blood Chemistry
What Does "Your Blood Tests Are Normal" Actually Mean?
The phrase that ends more clinical conversations than it should. What the reference range is actually measuring — and what it consistently misses.
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Blood Chemistry
The Ferritin Reference Range Problem: Why 30 is Not the Same as 80
The lab says normal. The patient feels terrible. Understanding why the ferritin range used in standard practice is set far too low to reflect optimal function.
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Blood Chemistry
What is HOMA-IR? The Insulin Resistance Test Your GP Doesn't Run
Fasting glucose and HbA1c tell you when the problem is already established. HOMA-IR tells you it's developing — years before the thresholds are crossed.
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Gut Health
Five Things a GI-MAP Stool Test Reveals That a Standard Blood Panel Misses
Pathogen burden, gut immune function, microbiome composition, digestive enzyme output — none of these appear on a standard NHS blood panel. The GI-MAP reads all of them.
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Metabolism
Why Can't I Lose Weight Despite Eating Well and Exercising?
The question I hear more than almost any other. When the conventional answer — eat less, move more — has been tried and failed, the investigation needs to go deeper.
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Neurodivergent
ADHD Diagnosis Wait UK: What to Do While You're Waiting
NHS ADHD assessment waits run to years in most regions. What functional medicine investigation reveals in the interim — and what can be addressed without a diagnosis.
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Clinical
The Peptide Conversation Nobody Is Having Honestly
Peptides are moving from research to practice faster than the clinical conversation is keeping up. An honest assessment of what the evidence actually supports.
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About
What Is FDN? The Training Behind the Test, Don't Guess Approach
Functional Diagnostic Nutrition — the methodology, the training, and why it forms the clinical foundation of the Detective Health approach.
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The book

Test, Don’t Guess — why your tests are normal and you still feel terrible.

The clinical method behind every investigation. 5 tests, 900+ data points, 7 body systems.

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Interpretation Guides
Topics
Blood chemistry Gut health Hormones Thyroid Iron Stress Medication Nutrition Testing
About Stephen

Stephen Duncan MSc FDN-P is an Edinburgh-based functional medicine practitioner with 37 years of clinical experience. Founder of Detective Health and the Test, Don’t Guess approach.

Follow on Instagram: @stephenduncan_guthealth

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