The debate about what makes us sick — the pathogen, the host, or some interaction between the two — is older than modern medicine and more alive than most people realise. Covid forced a generation to engage with it. The honest answer is more interesting than either camp wants to admit.
During the Covid years I went down most of the rabbit holes. Not in a panicked way — in the way a clinician who has spent 37 years questioning the first answer goes down rabbit holes. Deliberately, with note-taking, and with the specific intention of coming back out with a clearer understanding rather than a more comfortable one.
I looked at the virology — the isolation methodology, the transmission studies, the spike protein, the vaccine mechanism and its limitations, the emerging data on natural immunity. I read the establishment position and I read the dissenters. I read Malcolm Kendrick on the cardiovascular implications and Uffe Ravnskov on the cholesterol parallel — the pattern of an inconvenient finding being systematically marginalised because it threatened a profitable consensus. I read the terrain theorists who argued that the host mattered more than the pathogen. I read thinkers like Andrew Kaufman whose exosome argument — that what we call viruses may in some cases be endogenous cellular communication particles rather than external infectious agents — is intellectually serious even where the conclusion is contested. I encountered the position that no virus has ever been properly isolated under Koch's postulates, and I spent time with that argument rather than dismissing it.
And Thomas Cowan and Sally Fallon Morell's The Contagion Myth — which questions the foundational assumptions of germ theory from a terrain and electromagnetic perspective — I read that too. It stretches further than the evidence comfortably supports in places. But it asks important questions that the mainstream did not want asked, and in my experience those are often the questions most worth sitting with.
What I want to do in this post is lay the spectrum out honestly. Not to tell you what to believe. To show you the full range of thought, explain why each position exists, flag where the evidence is strong and where it is thin, and then tell you where my own clinical position actually lands — and why, practically speaking, it may not matter as much as both sides of the debate think it does.
"The most important health question Covid raised was not 'how do we avoid the virus?' It was 'why did the same exposure produce such radically different outcomes in different bodies?'"
The germ-versus-terrain debate has a specific origin point, and understanding it helps clarify why the argument has never fully resolved.
Louis Pasteur, working in the second half of the nineteenth century, developed and championed the germ theory of disease — the idea that specific microorganisms cause specific diseases, and that the route to preventing and treating illness is to identify and eliminate those organisms. His work on fermentation, pasteurisation, and the anthrax and rabies vaccines was transformative. Germ theory became the foundation of modern microbiology, infectious disease medicine, and the pharmaceutical model of treatment.
His contemporary Antoine Béchamp held a different view. Béchamp argued that microorganisms were not the primary cause of disease but a consequence of it — that the internal environment, or terrain, determined whether microbes became pathogenic, and that the same organism could behave differently depending on the host conditions it encountered. He proposed the concept of pleomorphism — that microorganisms could change form and function in response to their environment — a concept that mainstream biology rejected but that has never entirely disappeared.
Pasteur is reputed, on his deathbed, to have said: "Bernard had it right. The pathogen is nothing. The terrain is everything." Whether he actually said it is disputed. That the sentiment captures something real is not.
Claude Bernard — the third figure in this triangle — had argued for the importance of the milieu intérieur, the internal environment, as the primary determinant of health. His framework sits between Pasteur and Béchamp: the germ matters, and the terrain matters, and understanding their interaction is where the real clinical insight lives.
Pasteur: the pathogen causes the disease. Béchamp: the terrain determines whether the pathogen causes disease. Bernard: the internal environment is the primary variable. All three were right about something. The binary that developed between germ theory and terrain theory was a political and commercial construction as much as a scientific one.
Robert Koch's postulates, published in 1884, set out the criteria for establishing that a specific microorganism causes a specific disease. In their original form they require: that the organism be found in all cases of the disease; that it be isolated from the diseased host and grown in pure culture; that the cultured organism cause disease when introduced into a healthy host; and that the organism be re-isolated from the experimentally diseased host and shown to be identical to the original.
These postulates were a genuine advance — they created a testable standard for causal attribution that had not previously existed. They also have well-documented limitations that even mainstream microbiology acknowledges. They do not work cleanly for organisms that cannot be cultured in isolation. They do not work for organisms whose pathogenicity depends on host factors. They were designed for bacteria and do not map straightforwardly onto viruses, which are obligate intracellular replicators — they cannot replicate outside a host cell, which makes the "pure culture" criterion impossible in its original form.
This is why Koch's postulates were adapted — first by Thomas Rivers in 1937 for viruses, and later by Stanley Falkow for molecular microbiology. The adaptations are not an admission of defeat. They are science doing what science should do: revising methodology when the original tools do not fit the phenomenon being studied.
The argument that "viruses have never been proven to exist because they cannot be isolated under Koch's postulates" treats the original postulates as a fixed and final standard rather than as one methodology among several. It is a legitimate philosophical challenge to the isolation methodology used in virology. But the logical leap from "the isolation methodology is imperfect" to "therefore the entities do not exist" is not supported by the totality of the evidence — electron microscopy, genomic sequencing, and the reproducible clinical and epidemiological patterns of viral illness all point in the same direction.
Where this line of thinking has genuine value is in forcing a harder look at the standards of evidence used to establish causation in virology — a scrutiny that the field arguably needed and that has produced better methodology as a result.
I have spent time at every point on that spectrum. I hold positions 02 through 05 with varying degrees of confidence. I find position 06 intellectually interesting and worth following. I do not hold position 07 as a clinical conclusion — but I think engaging seriously with it sharpened my understanding of what I do hold and why.
The pandemic was, among other things, the largest uncontrolled experiment in public attitudes to health and personal responsibility that most of us will ever witness. And it revealed something important: the two extreme positions on the spectrum were, in different ways, both abdicating the same responsibility.
The fully pro-vaccine, comply-and-mask position, at its most passive, was an act of faith that the State and the pharmaceutical industry would manage your health on your behalf. Get the jab, follow the rules, trust the institutions. Personal biology — your nutritional status, your immune health, your underlying conditions, your vitamin D level — was largely irrelevant to the official public health message. The implicit promise was that the intervention would protect you regardless of the state of the host.
The "no virus" position, taken to its logical conclusion, is a different kind of abdication. If there is no pathogen and no contagion, there is no external threat to defend against, no reason to consider transmission or your effect on vulnerable others, and — crucially — no particular reason to build host resilience either, since the illness you might develop is a product of your own internal terrain rather than anything you have encountered. In its extreme form it dissolves both collective responsibility and individual health-building imperative simultaneously.
The radical middle — the position that the threat is real, the host matters enormously, and your job is to build the most resilient possible biology regardless of how the virology debate resolves — is the most clinically useful and the most intellectually honest. It requires the most work, which may be why it attracted the least attention during a period when most people wanted simple answers.
During Covid, the people I knew personally who had severe outcomes shared recognisable terrain characteristics: metabolic dysfunction, obesity, vitamin D deficiency, diabetes, cardiovascular disease, immune suppression from medication or chronic stress. The people who sailed through — including people in their seventies and eighties — had something different operating. Same exposure. Radically different outcomes. The host was not a secondary variable. It was the story.
I want to address something that comes up whenever heterodox thinking is discussed in health and science contexts: the Galileo argument. The claim that a minority position must be taken seriously because Galileo was a minority position, and Galileo was right.
This is partly correct and importantly incomplete. Galileo was right. He was also right at a time when the technology to definitively test his position did not yet exist in the form required to achieve consensus. His persecution was ideological and institutional, not based on a fair reading of available evidence.
The correct epistemological standard, as I have come to think about it, is not "this conclusion is wrong" but "this conclusion is not yet consistently evidenced or reproducibly demonstrated." Those are very different positions. The first closes a door. The second holds it open while being honest about where the evidence currently stands.
H. pylori as the cause of peptic ulcers was a minority position when Barry Marshall drank a Petri dish of the bacterium to prove his point and was widely mocked. It is now established medicine. The gut-brain axis — the idea that the microbiome communicates bidirectionally with the central nervous system and influences mood, cognition, and behaviour — was fringe twenty years ago. It is mainstream now. Mitochondrial dysfunction as a driver of chronic disease was not in the textbooks when I trained. It is a growing and serious field today.
The lesson is not that fringe positions are usually right. Most are not. The lesson is that the absence of current consensus does not equal the absence of future evidence, and that the method of inquiry matters as much as the conclusion. A position that is testable, that makes falsifiable predictions, and that follows the evidence wherever it leads — even when that is uncomfortable — deserves engagement rather than dismissal.
"The correct standard is not 'this conclusion is wrong' but 'this conclusion is not yet consistently evidenced.' Those are very different positions. One closes a door. The other holds it open honestly."
Blastocystis is a protozoan found in the gut of a significant proportion of the human population — estimates range from 20% to over 50% in some populations. It is routinely reported as a pathogen on stool testing. And yet the clinical picture is more complicated than a simple pathogen-causes-disease model suggests.
Studies have found Blastocystis in completely asymptomatic individuals with healthy, diverse microbiomes. Other studies have found associations with IBS, gut permeability, and systemic symptoms. The emerging picture is of an organism whose pathogenicity is context-dependent — in a depleted microbiome, it occupies and expands into niches that a healthy microbial ecosystem would not leave available. In a diverse, resilient gut environment, it may be essentially neutral or even part of a complex ecological balance.
This is not germ theory and it is not pure terrain theory. It is the interaction model — the organism and the host environment together determining the outcome. That is where the most interesting and clinically useful thinking in this space is happening.
H. pylori is present in roughly half the global population. In most people it causes no clinical symptoms. In some it is associated with gastric ulcers, gastritis, and — in the context of additional cofactors — an elevated risk of gastric cancer. Marshall and Warren won the Nobel Prize for demonstrating the bacterial cause of peptic ulcer disease, overturning decades of dogma that stress and stomach acid were the sole culprits.
But the story has developed since then. There is growing evidence that H. pylori plays a co-evolutionary role in immune regulation — that its presence in childhood may modulate immune development in ways that reduce allergic and autoimmune risk. Some researchers argue it should be considered a commensal organism in many contexts rather than a pathogen to be eradicated.
Again: the organism is real. Its effects are context-dependent. The host terrain determines whether it behaves as a threat or a neutral inhabitant. The binary of pathogen versus safe organism is inadequate to capture what is actually happening.
H. pylori positive findings are common. What changes the clinical significance is the context — is secretory IgA adequate? Is the rest of the microbiome diverse and robust? What is the inflammatory picture? A positive H. pylori in a client with depleted commensal bacteria, elevated beta-glucuronidase, low secretory IgA, and multiple gut symptoms is a different clinical picture from a positive result in someone with a healthy, diverse microbiome and no symptoms. The test tells you the organism is present. The full picture tells you what to do about it.
The vitamin C story is a useful lens on how the same substance, in different doses and contexts, can do opposite things — which maps directly onto how the same organism in different host contexts can produce opposite outcomes.
At physiological doses, vitamin C is an antioxidant — it donates electrons to neutralise reactive oxygen species and supports immune function, collagen synthesis, and iron absorption. At pharmacological doses — the kind used in high-dose intravenous protocols in cancer research — vitamin C becomes pro-oxidant in certain conditions. In the presence of free iron and the relatively lower catalase activity of cancer cells compared to normal cells, high-dose vitamin C generates hydrogen peroxide that is selectively toxic to tumour cells while leaving normal cells relatively unharmed.
This is not contradictory. It is dose-dependent and context-dependent pharmacology. The same molecule. Different doses. Different cellular environments. Different effects. The research into high-dose vitamin C and glutathione production — including work connected to whey protein supplementation and its role as a cysteine donor for glutathione synthesis — sits at exactly this intersection of nutritional biochemistry and oncology.
The lesson for the germ-host debate is the same: the question "is this organism dangerous?" cannot be answered without specifying "dangerous to whom, in what context, at what dose, in what host environment?"
There is a clinical observation that sits underneath all of the above and that, in my view, makes the germ-versus-terrain debate practically resolvable even if it is not theoretically resolved.
The body runs extraordinary compensatory mechanisms under nutritional and metabolic stress. It has adapted over hundreds of thousands of years to function under conditions of periodic insufficiency — fasting, seasonal food scarcity, periods of high demand. Those adaptations are remarkable. They are not infinite. And they have a cost.
When the deficit is chronic rather than acute — when the demand is consistently higher than the supply — the compensatory mechanisms that normally maintain homeostasis begin to fail in predictable sequence. Detoxification capacity declines. Immune surveillance degrades. Inflammatory resolution slows. DNA repair becomes error-prone. The internal environment shifts from one that is hostile to pathogens and aberrant cells to one that is permissive to both.
This is where the germ-host interaction becomes clinically actionable regardless of where you sit on the theoretical spectrum. If you hold position 01 — it is the germ — then building a robust host makes you more resistant to the germ and more capable of clearing it if infected. If you hold position 04 — it is the terrain — then building a robust host addresses the primary cause directly. If you hold position 07 — there is no virus — then building a robust host addresses whatever internal dysregulation is producing what gets misattributed to viral infection. In every case, the answer is the same: build the host.
I do not need the germ-terrain debate to be resolved to know what to do clinically. I need to know the state of my client's terrain — their nutritional status, their inflammatory load, their gut microbiome, their HPA axis function, their detoxification capacity. Those things are testable. They are addressable. And addressing them improves outcomes regardless of which theoretical framework turns out to be correct.
That is not a dodge. It is the most honest clinical position available. The debate is intellectually fascinating. The practice is straightforward: measure the terrain, address what you find, and let the biology work for the person in front of you.
I want to say something directly about the intellectual experience of engaging seriously with heterodox positions, because I think it is undervalued in clinical practice and overvalued in online wellness culture — simultaneously and in different communities.
Going down the rabbit hole on cholesterol in the early internet era — reading Karl Loren's sprawling text-heavy website, printing off forty-page articles because there was no other way to save them, following the thread from there to Malcolm Kendrick, to Uffe Ravnskov and the Cholesterol Sceptics, to the broader question of how scientific consensus gets manufactured and maintained — that was one of the most valuable intellectual experiences of my clinical career. Not because every conclusion I encountered was correct. Most were not, or not entirely. But because the process of seriously engaging with a counter-narrative forces you to interrogate your own assumptions with a rigour that comfortable agreement with the consensus never demands.
The same was true of the no-virus rabbit hole. I did not emerge from it believing there are no viruses. I emerged from it with a much clearer understanding of what I do believe about virology and why, what the actual limitations of the isolation methodology are, what the exosome distinction means and does not mean, and where the genuine uncertainty in the field lives. The head-hurting is productive. The confusion that comes from taking a hard position seriously is preferable to the false clarity that comes from never having tested it.
The risk is not in going down. It is in not coming back up. The people who enter the no-virus position as a permanent worldview — or the simulation hypothesis, or any other total explanatory system that dissolves the need for further inquiry — have usually found something that feels more satisfying than uncertainty. Certainty is comfortable. It is not the same as understanding.
The Test, Don't Guess philosophy is an epistemology as much as a clinical methodology. It says: hold your position lightly, test your assumptions wherever you can, follow the evidence wherever it leads, and be honest about the distance between what you know and what you believe. That applies to the germ-terrain debate as much as it applies to a client's cortisol pattern or their GI-MAP results.
The terrain argument applied specifically to cancer — immune surveillance, nutrient depletion, the conditions we create over years — is covered in Cancer Doesn't Happen in a Vacuum. The cholesterol-inflammation distinction and the follow-the-money history of dietary guidelines is in Follow the Money: Seven Health Narratives That Got Distorted.
After 37 years in clinical practice, four books, and a significant amount of time in the rabbit holes — here is my honest position.
Pathogens are real. Viruses are real. Contagion is real. The evidence for their existence and their capacity to cause disease is not manufactured. But the orthodox germ theory model — in which the pathogen is the primary variable and the host is largely a passive recipient — is demonstrably incomplete as a clinical framework. The host is not a secondary variable. In most cases of chronic illness and in many cases of infectious disease, the host is the primary story.
The same pathogen in different hosts produces radically different outcomes. That is not theoretical. It is observable, measurable, and actionable. The factors that determine which outcome you experience — your nutritional status, your inflammatory load, your gut integrity, your sleep quality, your stress history, your HPA axis function — are all modifiable. All testable. All within the scope of what functional medicine can address.
The fringe positions on the spectrum have contributed something real even where their conclusions are wrong. The terrain theorists forced a reckoning with the limits of the seed model. The exosome researchers asked important questions about the precision of viral isolation methodology. The cholesterol sceptics were eventually vindicated in their core claim even while being marginalised for decades. Holding the door open to heterodox thinking, while being rigorous about the standard of evidence required to act on it clinically, is not a compromise. It is the correct scientific posture.
And practically — whether the germ or the terrain wins the theoretical argument — the clinical answer is the same. Build the host. Test comprehensively. Address what you find. Give the biology what it needs to function at its best. Everything else is a fascinating conversation for a long evening with a good whisky.
If you want to understand where your own terrain actually stands — start with the Health Pattern Finder. Or book a call and we will look at the data together.
Wherever you sit on the germ-terrain spectrum, the clinical answer is the same — understand your terrain, address what you find, and give the biology what it needs. The TDG Five-Test Programme is where that investigation starts.
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