The nutrition conversation has a fundamental problem. It treats human metabolism as though it operates on a single template — as though the macronutrient ratios, food combinations, and eating patterns that produce good outcomes in the average clinical trial will produce good outcomes for you specifically. They often don’t. And the reason is not willpower, discipline, or adherence. It is biology.
Metabolic typing — the clinical framework developed most comprehensively by Bill Wolcott at Healthexcel, building on the foundational work of Weston Price, Francis Pottenger, Roger Williams, and William Donald Kelley — is the systematic approach to identifying how an individual’s metabolism is configured and what dietary approach is therefore most appropriate for them. It is the clinical science behind why your friend lost fifteen kilograms on keto and you gained two, why you feel terrible on a high-protein diet that made your colleague feel extraordinary, and why generic dietary advice produces such inconsistent results across different people.
The TDG clinical approach is built on the Healthexcel system. The six Metabolic Nature types are the framework through which we interpret not just dietary recommendations but supplement priorities, meal timing, macronutrient ratios, and the nutritional context in which functional test results make most clinical sense. Understanding your Metabolic Nature is the first layer of nutritional personalisation — the one that sits beneath everything else.
The Fundamental Concept — Two Dominant Systems
Metabolic typing rests on an understanding of two primary physiological systems that regulate energy metabolism, and how their relative dominance in an individual determines their nutritional needs.
The first is the autonomic nervous system — specifically the balance between sympathetic and parasympathetic dominance. The sympathetic nervous system drives energy mobilisation, stimulation, and the fight-or-flight response. The parasympathetic drives rest, digestion, tissue repair, and the conservation of energy. The relative dominance of one over the other has specific implications for how the body handles different macronutrients — sympathetic dominants tend to respond better to higher fat and protein intake, parasympathetic dominants to complex carbohydrates.
The second is the oxidative rate — the speed at which cells convert nutrients to energy through oxidative phosphorylation. Fast oxidisers burn through their fuel rapidly, require high-density nutrient sources (fat and protein) to sustain energy, and feel poorly sustained by carbohydrate-heavy meals. Slow oxidisers metabolise nutrients more gradually, tend to do better with carbohydrate as a primary fuel, and can feel heavy and sluggish on high-fat high-protein diets.
These two systems interact. A person who is simultaneously sympathetically dominant and a fast oxidiser has a particular metabolic configuration. Someone who is parasympathetically dominant and a slow oxidiser has a completely different one. The combination, along with several secondary systems covering cell permeability, blood type factors, and endocrine balance, produces the six Metabolic Nature types we use in clinical practice.
There is no universally healthy diet. There is the diet that is healthy for your specific metabolic configuration — which may be quite different from the diet that is healthy for the person sitting next to you. This is not a philosophical position. It is a clinical observation made by the same physicians who established the nutritional foundations of modern functional medicine.
The Six Metabolic Nature Types
Why This Explains So Much That Standard Nutrition Cannot
Consider Kevin — a man in his early sixties with abdominal fat accumulation, afternoon carbohydrate cravings, hair thinning, morning joint stiffness, and gradual weight gain despite no major lifestyle changes. His insulin resistance markers are significant. His thyroid pattern suggests impaired conversion. His inflammatory load is elevated.
A standard dietary recommendation for weight loss and insulin resistance might be: reduce total calories, reduce saturated fat, increase fibre and vegetables, moderate protein. Entirely reasonable as a population-level recommendation. But whether it works for Kevin specifically depends critically on his Metabolic Nature. A Kinetic type Kevin, for whom protein is the primary fuel source, will feel progressively worse on a calorie-restricted moderate-protein approach — he will be simultaneously underfuelling his dominant metabolic system and asking it to function efficiently on the wrong substrates. A Grounded type Kevin may thrive on exactly this approach.
This is not a hypothetical. It is the clinical observation that motivated the development of metabolic typing as a framework — the recognition that identical dietary advice produces entirely opposite results in different people, and that the variable is not compliance but metabolic individuality.
How Metabolic Nature Is Assessed
The clinical assessment of Metabolic Nature uses a structured questionnaire covering food reactions and cravings, energy patterns throughout the day, response to different meal compositions, sleep quality and patterns, stress response characteristics, physical characteristics, and health history. The questionnaire is available inside the Practice Better client portal as part of the TDG clinical intake process — it is one of the twelve intake forms completed before a paid consultation.
The questionnaire result gives an initial Metabolic Nature assessment. This is refined over time through food-symptom tracking and through the objective data from functional testing. Blood chemistry — particularly the glucose and insulin picture, the inflammatory markers, and the liver enzyme pattern — contextualises the Metabolic Nature assessment with hard data. The Organic Acids Test adds the cellular energy picture: which parts of the Krebs cycle are under stress, which cofactors are functionally depleted, which patterns of mitochondrial function are present. Together, the subjective Metabolic Nature assessment and the objective testing give a far more precise nutritional picture than either alone.
Food quality overrides macronutrient ratio. A Kinetic type eating poor-quality processed protein performs worse than a Grounded type eating high-quality whole food carbohydrates. The type tells you the direction; quality determines how far you can travel in it.
The ideal ratio shifts with health status. Someone with significant gut dysbiosis may temporarily need a modified approach to their Metabolic Nature while the gut heals. The type provides the nutritional destination; clinical status determines how directly you can travel there.
Breakfast determines the day for most types. The first meal sets the metabolic tone. A Kinetic type eating cereal and juice for breakfast is starting the day in metabolic deficit. A Grounded type eating three eggs and bacon may feel cognitively sluggish before midday. The first meal is the highest-leverage single dietary change for most people.
Supplements are type-specific. The supplement protocols appropriate for a Kinetic type and a Grounded type are different even when their functional test results show similar deficiencies — because the underlying reason for the deficiency and the metabolic context in which it operates differs by type.
The Nutrition Integration Engine
Within the TDG clinical tool suite, Metabolic Nature sits at the top of what we call the Nutrition Integration Engine — the six-layer framework that resolves conflicting dietary recommendations from different data sources into a coherent, actionable nutritional approach.
The hierarchy: Metabolic Nature is the first layer — the constitutional baseline that everything else is built on. Absolute exclusions come second — medically confirmed intolerances and allergies that override all other recommendations. The digestive ceiling comes third — what the gut can currently process, which may limit the ideal Metabolic Nature diet during gut healing. Blood chemistry findings come fourth — inflammatory load, glucose handling, and nutrient deficits that require targeted dietary compensation. DUTCH and OAT findings come fifth — hormonal and cellular context. And implementation context comes sixth — practical constraints around food access, cooking capacity, budget, and lifestyle that determine what is actually achievable.
The Metabolic Nature is the foundation of this hierarchy because it is the most constitutional factor — the one that reflects how the person’s metabolism is fundamentally configured rather than how it is currently performing due to illness, stress, or deficiency. Address the Metabolic Nature first, then layer the clinical findings on top of that foundation.
The reason metabolic typing produces such consistently good clinical results, in my experience, is not that it is complicated. It is that it is honest about the one variable that most nutritional advice pretends doesn’t exist: that human metabolism is individually variable in ways that matter enormously for what a given person should eat. Acknowledging that variable — and building the dietary approach around it — is what distinguishes personalised nutrition from generic advice, and what determines whether a dietary protocol will hold over the long term or become the latest in a long list of things that worked for everyone else but not for you.