My FDN Certification Review: Why I Changed How I Investigate Health

I have been helping people improve their health since I was 18 years old. I started as an athletics and boxing coach. By my mid-twenties I had a science degree, a serious interest in nutrition, and more opinions about what worked and what didn't than most people twice my age. Along the way I added an MSc, a Postgraduate Certificate in Health Informatics, postgraduate training under Paul Chek, advanced metabolic typing certification under Bill Wolcott, and a lot of time in clinical practice watching what happened when the theory met real human beings.

None of that prepared me for the one type of client I kept encountering and couldn't fully serve. You'll know this client if you've worked in health for any length of time. Their bloods come back normal. Their GP finds nothing of concern. And yet they are clearly not well — tired in a way that sleep doesn't fix, struggling with weight that doesn't respond to the obvious interventions, digestion that never quite settles, hormones that seem permanently off. They've already tried different diets and different supplements. Some things help a little; nothing gets to the bottom of it. Some of them have started to wonder if it's all in their head.

That client is why I went looking for Functional Diagnostic Nutrition. And what I found when I got there reorganised the way I work more fundamentally than anything else in the twenty years before it.

Where I Started — And Why It Wasn't Enough

My undergraduate years at university coincided with the peak of low-fat orthodoxy. In second-year physiology, the Framingham Heart Study findings were presented as settled science: saturated fat and cholesterol cause heart disease. Six years of university only reinforced that position. It took several years of working with real clients, studying hormones, and watching what happened when people followed that advice, before I started questioning it seriously.

Once I understood how steroid hormones — cortisol, testosterone, oestrogen — are synthesised from cholesterol, the low-fat model started to look less like settled science and more like an expensive error. That was the beginning of a longer process of following evidence wherever it led, rather than wherever it had been pointed.

Over the years that followed I built a significant toolkit. I studied under Paul Chek. I trained with Bill Wolcott and became one of the few people in the UK holding advanced metabolic typing certification through Healthexcel. I incorporated DUTCH hormone testing, food sensitivity analysis, and organic acids testing into my practice. I built a multidisciplinary clinical practice. I co-founded Omnos, a functional laboratory platform that's now integrated with Regenerus Labs.

By the time I enrolled in FDN, I was already running functional labs with clients. I was already looking at hormones, digestion, and metabolism in an integrated way. What I didn't have was a system that connected all of it reliably, case after case, into something reproducible.

The Problem With Pieces Without a System

This is the thing nobody tells you about accumulating clinical knowledge over decades: you can end up with extraordinary depth in individual areas and still lack the connective tissue that ties it into a coherent, repeatable methodology. Each client case felt like building from scratch. When you're dealing with people whose issues span multiple body systems simultaneously — hormones feeding into gut function, gut function feeding into immune response, immune response feeding into energy production — you need more than knowledge. You need a methodology.

That is what FDN gave me. You can explore FDN here.

What FDN Actually Is

Functional Diagnostic Nutrition was developed by Reed Davis. His name was already familiar to me — he moved in the same circles as Paul Chek and Bill Wolcott, people whose work I respected. The core principle is the same one that runs through everything I do now: test, don't guess. Instead of matching symptoms to probable causes and building a protocol around a hypothesis, FDN teaches you to run a specific set of functional labs, interpret what you find across multiple body systems simultaneously, and build your recommendations around the data.

The goal isn't a diagnosis. The goal is what Reed calls healing opportunities — areas of dysfunction that, once addressed, allow the body to do what it's designed to do. That distinction matters. You're not trying to name the problem. You're trying to find where the system is breaking down and give it what it needs to restore itself.

The assessment framework is organised around six categories Davis calls H.I.D.D.E.N.: Hormones, Immune function, Digestion, Detoxification, Energy production, and Nervous system regulation. These are the six areas functional lab testing is designed to screen simultaneously. Not one at a time. All six, looked at together, so you can see how dysfunction in one area is driving problems in another.

For someone who had already been testing for years, this wasn't a revelation about the value of lab data. It was a revelation about how to use it systematically.

What the Training Was Actually Like

FDN is self-paced, but that description undersells the depth. The curriculum covers stress and hormone physiology in two dedicated modules, metabolic health, digestive health, antigens and pathogens, food sensitivities, metabolic typing, the D.R.E.S.S. for Health Success protocol — Diet, Rest, Exercise, Stress Reduction, Supplementation — and you work through all of it while running the functional labs on yourself.

That last part is not incidental. Running the labs on yourself is the point. You don't learn to interpret results theoretically and then apply that theory to clients. You get your own data, sit with a mentor, and go through what you find. I had run plenty of labs on clients. But seeing the full FDN assessment applied to my own physiology, through a structured interpretive lens, was a qualitatively different experience. You understand something differently when the data is yours.

A few things stand out looking back:

The H.I.D.D.E.N. framework. What makes it powerful is not any single test — it's the fact that you're looking at all six categories simultaneously. Gut dysfunction is almost always an immune issue as well. Hormonal chaos almost always has a digestive or detoxification driver. The framework forces you to hold the whole picture, which is exactly what individual specialist appointments prevent you from doing.

The D.R.E.S.S. protocol. The components aren't novel. The way FDN teaches you to apply them — sequenced by lab findings, specific to each client's pattern of dysfunction, revisited as markers improve — is what makes the difference. It becomes the backbone of every client interaction rather than a generic lifestyle checklist.

The mentorship structure. Weekly live calls. One-to-one reviews of your own lab results. A community of practitioners who are doing this work seriously. If you've done online certification programmes that leave you to figure things out on your own, FDN is notably different. The access to Reed Davis directly, and to the lead instructors, is substantial.

The Medical Director Programme. This gives practitioners legal access to order over 70 functional labs without a medical licence. For anyone building a serious functional health practice outside of a clinical medicine structure, this changes what's possible.

One caveat on that last point, because it is the part most often repeated without checking: lab access is a United States framing. It does not transfer to the UK. Nutritionist is an unprotected title here, dietitian is protected, and what you may say about a result is governed by advertising and consumer-protection rules rather than by who is permitted to order the test. I have written that distinction up in full on the GLP-1 page, and for UK practice generally on FDN in the UK.

What Changed in Practice

Professionally, completing FDN gave me what I had been trying to build for years: a single integrated system that connects testing, interpretation, and protocol design into one repeatable process. I no longer start a client engagement by guessing what might be going on. I start by investigating.

The TDG Five-Test Programme I now run through Detective Health is built directly around this model. Five integrated functional tests — blood chemistry, GI-MAP stool analysis, DUTCH Plus hormones, organic acids testing, and food sensitivity analysis — read together, interpreted through the FDN framework and my own nearly forty years of working with people. The clients who benefit most are exactly the ones I kept running into before I found FDN: people who've been told their bloods are fine but don't feel fine, people with stubborn weight and unresolved digestive issues and hormonal disruption who have been managing symptoms rather than finding what's actually driving them.

On a practical level, the consistency I now have across cases has also made me a better communicator. When you can show someone precisely where their labs are falling short of optimal function — not just whether they're within the normal range, which tells you almost nothing useful — the conversation changes. People understand why they feel the way they do. That understanding is often the first thing that actually helps.

Who This Is For

If you're a health practitioner, personal trainer, or nutrition professional who feels like you're working hard and getting inconsistent results, FDN is worth a serious look. Particularly if you're already curious about functional lab testing but don't have a system to use it reliably. Or if your clients follow your recommendations and improve partially but never fully. Or if you keep encountering people whose conventional medical results don't explain their symptoms, and you know something is being missed, but you're not sure what to do with that.

You don't need a clinical background to enrol. You need intellectual curiosity, a genuine commitment to finding what's actually going on with your clients rather than managing what's on the surface, and the willingness to do real work — including on yourself.

I enrolled because I had pieces without a system. FDN gave me the system. Practising it since 2009, and a five-test programme later, it remains the most rigorous and most practically useful clinical training I've completed.

Who It’s Not For — and What It Costs

The cost. When I checked FDN’s payment page on 4 October 2026, it listed two instalment plans: 12 monthly payments of $716.42, or 24 of $383.21. That is about $8,600 or $9,200 in total. The page doesn’t name the currency; FDN is a US company, so read them as US dollars. I didn’t see a pay-in-full price. Check the current figure yourself before deciding (FDN payment page). On top of that come your own lab costs while you train, and the cost of finding clients afterwards.

It suits coaches, trainers and therapists who want a testing-led method and are prepared to run a business, not just learn a method.

It doesn’t suit you if:

• You want a regulated title. FDN-P is a certification from a private training company, not a regulated profession.
• You want to diagnose or treat disease. In the UK an FDN-P does neither. What you can and can’t say about a result is set out in FDN in the UK.
• You expect the certificate to bring clients. It won’t. Marketing does. FDN publishes pages about what practitioners can earn; treat those as marketing, and don’t plan around the figures.
• You can’t fund lab costs, and the months it takes to build a client list, alongside the fees.

What I would do first: take the free sample modules (the “Try FDN Free” link below), and read Module 01 of my clinical manual, which is free. Both before you pay anything.

How I use it now. What FDN gives you is a repeatable, test-led system and real mentorship, and it’s designed to be taken as a whole: the tests, D.R.E.S.S. and the coaching together. In my own practice I hold every test and recommendation to an evidence-first standard, and I publish it when I change my mind (my corrections page). That has moved how I read a couple of tests. I read a zonulin result cautiously (more in intestinal permeability), and I use IgG food results as leads for a supervised elimination and reintroduction rather than an avoidance list. That’s my choice for my clients, not a verdict on the training.

I earn a commission if you enrol through the links on this page. That is why the costs and the reasons not to enrol are here too.

What I Wrote Down Afterwards

The thing FDN gave me was a system. What I did with it over the following years was write the system down — not the FDN curriculum, which is theirs, but my own clinical reasoning built on top of it: why a test gets ordered, what a marker means when it sits inside the laboratory range and outside the optimal one, and how a gut finding and a hormone finding turn out to be one problem rather than two.

That is the TDG Clinical Manual: thirteen modules, around eight hours of reading. Module 01 is free and complete — the one about why the advice you have already followed probably did not work. No email required to read it. The other twelve are £97. The £97 comes off the TDG Five-Test Programme if you enrol as a client within 60 days of buying the manual. It isn’t credited against single tests or combined with the retest discount.