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A Framework for Deciding Where to Start

Metabolic
Natures

Every diet works brilliantly for someone and badly for someone else. Metabolic Natures is a structured way of working out which end of that you are on — two physiological axes, read together, with the strength of each shown rather than hidden. It is a starting point, not a test result, and this page says exactly what the evidence for it is.

Get the Book on Amazon → How a reading works ↓
AXIS 1 · OXIDATIVE SLOW FAST ENDURANCE slow ADAPTIVE mixed CATALYST fast AXIS 2 · AUTONOMIC PARA SYMP GROUNDED recovery CALIBRATED balanced KINETIC activation You get a position on each — with a percentage. E.G. FAST-OX 73% · PARASYMPATHETIC 37%
The Core Question

Why does every diet work
for someone — but not for everyone?

For decades, the nutrition conversation has been dominated by competing dietary ideologies — low fat, low carb, paleo, ketogenic, carnivore, plant-based. Each has its passionate advocates. Each has its disillusioned failures. And each keeps generating the same pattern: it works brilliantly for some people and makes others feel significantly worse.

This is not a paradox. It is what you would expect from applying population-level dietary advice to individuals. The person who does well on high protein and fat is not obviously the same metabolic system as the person who does well on complex carbohydrates. The difference is not willpower or adherence.

Metabolic Natures is the framework we use to decide where to start. Two physiological axes — how quickly your cells burn fuel, and where your nervous system sits between activation and recovery. Three positions on each axis, and the six names in the book are those positions: Endurance, Adaptive and Catalyst on the oxidative axis; Grounded, Calibrated and Kinetic on the autonomic one. You are not one of six types. You get a reading on both axes, each with a percentage — and the percentages matter more than the names.

"The question was never which diet is correct. The question was always which metabolic system it was operating on — and whether those two things were compatible."

What this is, and what the evidence for it actually is

Metabolic Natures is a framework for deciding where to start, not a test result.

The general idea is well supported: people do better on different balances of food, and the balance someone can actually sustain is the one that works. Dansinger and colleagues randomised 160 people to four named diets for a year and found weight loss correlated with how well people stuck to the plan (r = 0.60) and essentially not at all with which plan it was (r = 0.07, not significant). DOI

The specific categories are not validated by controlled trials, and we do not claim they are. No trial has tested whether assigning someone to an oxidative or autonomic category, and matching a macronutrient ratio to it, produces a better result. The closest test of that shape of argument is DIETFITS — 609 adults, healthy low-fat against healthy low-carbohydrate, twelve months, a difference of 0.7 kg between arms, and neither a genotype pattern nor baseline insulin secretion predicted which diet suited whom. DOI DIETFITS did not test oxidation rate or autonomic tone, so it is not a direct refutation — but it tested the logic, and the logic did not hold up.

So what are we claiming? That a structured way of recognising your own long-standing pattern, adjusted from what your test findings currently show, gives you an approach you can recognise yourself in and therefore sustain. And one thing more, which is the part that can be wrong: we write down, before your protocol starts, what we expect to change and by when — and we check it at retest. That prediction can come back not met. Nothing else in the framework can.

Read the correction to Chapter 6 of the book →

A READING, IN FULL 1 · OXIDATIVE Endurance Adaptive Catalyst 73% 2 · AUTONOMIC Grounded Calibrated Kinetic 37% Fast-oxidative dominant, 73% Parasympathetic subdominant, 37% SHORTHAND: CATALYST-GROUNDED

Two axes, read together — with the strength of each shown

Metabolic Nature sits at the intersection of two physiological systems that vary between people. We report both, always — a dominance and a subdominance, each as a percentage. Label order is fixed: oxidative first, autonomic second.

Reporting only the stronger of the two was the biggest defect in the original scoring. When the two are close, a one-point change to a single questionnaire answer flips the label — and a flipped label means a different food guide. Showing both, with percentages, removes the flip rather than hiding it.

01

Cellular oxidation rate

How quickly cells convert fuel into usable energy. Faster oxidation tends to suit more protein and fat; slower oxidation tends to suit more carbohydrate. Positions: Endurance (slow), Adaptive (mixed), Catalyst (fast). Read from the questionnaire. Krebs-cycle intermediates and fatty-acid oxidation markers on an organic acids test describe what your mitochondria are doing now — a related but different question.

02

Autonomic nervous system balance

Where you sit between sympathetic activation and parasympathetic recovery. Positions: Grounded (parasympathetic), Calibrated (balanced), Kinetic (sympathetic). Read from the questionnaire, and described by the cortisol diurnal curve on a DUTCH panel. This page previously listed a calcium:phosphorus ratio and an eosinophil:basophil pattern here. Both have been removed — this is why.

Six Names, Two Axes

The six names are positions —
not six kinds of person.

How a reading is written

You get one position from each axis, each with a percentage. So a result reads fast-oxidative dominant at 73%, parasympathetic subdominant at 37% — Catalyst-Grounded as shorthand where a short label is needed.

Strength maps to dietary intensity as a gradient, not a category: a strong fast oxidiser sits toward a ketogenic emphasis, a 50–60% fast oxidiser toward moderate protein and lower carbohydrate. That is more honest than a hard category, because it shows how close to the middle you actually sit.

Axis 1 · Oxidative

How quickly you burn fuel. This sets the macronutrient framework.

Slow oxidative
Endurance
The aerobic position

Built for sustained low-intensity output. Tends to do well on steady-state fuelling and to use carbohydrate efficiently. Struggles with high-glycaemic loads and erratic eating patterns. Often the person who genuinely does well on a predominantly plant-based diet — not because the ideology is correct, but because the physiology happens to suit it.

Characteristic signals
  • Good endurance, struggles with explosive intensity
  • Does well on steady, moderate eating patterns
  • Manages well on lower protein intake
  • Sensitive to glycaemic load and meal timing
  • Often does well on plant-forward diets
Position read from: the questionnaire. Described — not confirmed — by Krebs-cycle intermediates and fatty-acid oxidation markers on an organic acids test.
Mixed oxidative
Adaptive
The middle position

Neither dominantly fast nor slow. Context-dependent — shifts with stress load, season and life stage. Adaptable in principle, unpredictable in practice. Often fails at both extremes: a pure ketogenic approach destabilises, a high-carbohydrate approach flattens. Where blocking factors are heavy, this is also where an unclear picture lands until they are addressed.

Characteristic signals
  • Inconsistent energy — responds unpredictably to food
  • Neither extreme diet feels right
  • Highly sensitive to stress-related dietary shifts
  • Mixed hunger patterns
  • History of several failed dietary approaches
Position read from: the questionnaire. Described — not confirmed — by Krebs-cycle intermediates and fatty-acid oxidation markers on an organic acids test.
Fast oxidative
Catalyst
The fast position

Moves through glucose and carbohydrate quickly. Tends to need protein and fat to hold steady through the day. Carbohydrate-heavy eating is more likely to produce blood sugar swings, edginess and energy crashes. Generally does better on denser fuel at regular intervals.

Characteristic signals
  • Energetic, but crashes on carbohydrate-led meals
  • Strong appetite, gravitates to protein and fat
  • Struggles on high-carb or low-fat approaches
  • Hungry again soon after a light meal
  • Often reports doing well on lower-carbohydrate eating
Position read from: the questionnaire. Described — not confirmed — by Krebs-cycle intermediates and fatty-acid oxidation markers on an organic acids test.
Axis 2 · Autonomic

Where you sit between activation and recovery. This modifies the framework the first axis sets.

Parasympathetic
Grounded
The recovery-weighted position

Sits toward the restorative end. Slower to get going in the morning, better later in the day, digestion-forward, and easily over-stimulated by caffeine and by hard training too often. Under-recovery does not usually present as fatigue here — it presents as everything taking longer.

Characteristic signals
  • Slow to start, warms up through the day
  • Sensitive to caffeine and stimulants
  • Digestion generally comfortable when unstressed
  • Tolerates rest well, tolerates overreaching badly
  • Tends to under-eat rather than over-eat
Position read from: the questionnaire. Described — not confirmed — by the cortisol diurnal curve on a DUTCH panel.
Balanced
Calibrated
The middle position

Neither extreme. Reasonably well-regulated between activation and recovery. The position that conventional advice was implicitly written for — which is part of why standard guidance works for some people and not for others. Changes here tend to need less force than at either end.

Characteristic signals
  • Consistent, predictable energy across the day
  • Sleeps and wakes without much difficulty
  • Stress recovery is unremarkable
  • Responds to moderate, ordinary changes
  • Standard dietary guidance usually lands reasonably well
Position read from: the questionnaire. Described — not confirmed — by the cortisol diurnal curve on a DUTCH panel.
Sympathetic
Kinetic
The activation-weighted position

Sits toward the activated end. Quick to switch on, slower to switch off. Sleep onset, wind-down and appetite are usually the first things to go when load rises. Responds to structure and to deliberate down-regulation more than to more effort.

Characteristic signals
  • Wired in the evening, hard to wind down
  • Anxiety or reactivity under load
  • Appetite drops when stressed, then rebounds
  • Trains hard, recovers less well than expected
  • Caffeine tolerance masks the pattern rather than fixing it
Position read from: the questionnaire. Described — not confirmed — by the cortisol diurnal curve on a DUTCH panel.
Questionnaire and Tests

What the questionnaire does —
and what the tests actually do

Chapter 6 of the book has this the wrong way round, and the book contradicts itself on the point. Chapter 6 says the questionnaire measures your current functional expression and the tests reveal the constitutional type underneath. Chapter 7 says that sustained HPA axis dysfunction produces sympathetic indicators on both the questionnaire and the tests. If prolonged stress distorts the tests as well, the tests cannot be the window onto constitution that Chapter 6 claims.

Chapter 7 is the one that is right. The questionnaire is the closest available proxy for long-standing pattern — a starting hypothesis, not a measurement. The tests describe what your biochemistry is doing now. Where the two disagree, current function governs the protocol until the constraint clears. Read the full correction, dated →

What each panel actually tells us
Blood Chemistry · 46 Markers
Current metabolic state
Bicarbonate and CO₂ describe acid-base balance. Total protein and albumin describe catabolic versus anabolic tendency. Triglyceride:HDL describes how fat metabolism is running. Thyroid function modifies metabolic rate and can mask everything else. None of these has been tested against macronutrient response — they describe the current state, they do not assign an axis position.
Organic Acids Test · Krebs Cycle
Current mitochondrial pattern
Krebs cycle intermediates show where energy production is running efficiently or bottlenecked. Adipate and suberate are read as impaired fatty acid oxidation. Pyruvate and lactate patterns describe carbohydrate handling. Methylmalonic acid describes functional B12 status. Again: current function, and a reason to change the protocol — not a confirmation of the questionnaire.
DUTCH Plus · Hormone Panel
Current adrenal output
The cortisol diurnal curve describes where autonomic load currently sits. DHEA:cortisol maps anabolic against catabolic balance. Total metabolites describe overall output. This is the panel most likely to disagree with the questionnaire, and when it does, it wins for the duration of the protocol.
Corrections

What we removed from this page, and why

Deleting a claim quietly looks like covering a mistake. These were on this page until 8 September 2026.

Evidence grade: none

The calcium:phosphorus ratio

The calcium-to-phosphorus ratio reached this framework through hair tissue mineral analysis. In HTMA it is a hair measure, not a blood one, and it is read as an autonomic ratio — around 2.6 is taught as ideal, with a high ratio taken to indicate parasympathetic dominance and a low one sympathetic dominance. We had it on this page as a serum marker of fast oxidation above 2.5:1: the wrong specimen, the wrong axis, the wrong direction, and a figure closer to the middle of the range than to either edge.

It has never been tested against macronutrient response in any case. And in 2001 JAMA published a study in which a single hair sample, split between the six commercial laboratories handling most US samples, returned between-laboratory differences exceeding tenfold for twelve minerals, with nearly every mineral classified differently depending on the lab. Seidel et al., JAMA 2001;285(1):67–72. If split samples from one person disagree that badly, no ratio computed from them can be reliable — whatever the interpretation attached to it. We no longer present it as a marker.

Evidence grade: none

The eosinophil:basophil pattern

Presented here as an autonomic indicator. Searched in PubMed on 7 September 2026 for eosinophil and basophil with ratio and autonomic, sympathetic or parasympathetic: four papers returned, and not one uses an eosinophil:basophil ratio as an index of anything. One is mildly unhelpful to the claim — low birth weight predicted higher basophil and higher eosinophil counts together alongside blunted autonomic responses, which is not what a ratio index would predict. Removed. Scope of that search, stated so it can be challenged: PubMed only, English-language indexing.

Evidence grade: none

"Test-confirmed", and the genetic-baseline claim

This page used to be headed Six Types. One Framework. Test-Confirmed. No test confirms an axis position, because no test has been validated against one. The tests describe current function. That is useful and it changes protocols — it is not confirmation, and the word has been removed everywhere on this page.

The page also carried a section stating that SNPs governing oxidative phosphorylation and beta-oxidation establish a constitutional baseline. We are sometimes asked whether this is genetic. It probably has some genetic component — most physiological variation does — but no SNP panel has been tested against oxidative or autonomic position, we do not use one, and anyone selling you a gene test for your metabolic type is ahead of the evidence. The claim has been removed rather than softened.

The part that can fail

What counts as the constraint clearing

Where the tests disagree with the questionnaire, current function governs the protocol until the constraint clears. That phrase has to mean something checkable, so it does: the markers that define the constraint are named in advance, in writing, before the protocol starts, along with what change is expected in them and by when. They are retested.

There are three possible outcomes, and the third is the one that matters: the constraint clears and the picture shifts as predicted; the constraint does not clear, and the protocol continues; or the constraint clears and the expected shift does not happen. The third is a stated possible outcome, it is recorded as one, and it counts against the framework rather than being explained away.

An Important Distinction

Long-standing pattern vs current function

Long-standing pattern
What the questionnaire is reaching for
The way you have run for years, across different diets, jobs and life stages — the thing you recognise when you read it back. The questionnaire is the closest available proxy for it. It is a starting hypothesis, and it is the layer that decides where a protocol begins. It is not a measurement and we do not present it as one.
Current function
What the tests describe
HPA axis status, thyroid function, mitochondrial efficiency, nutrient cofactor availability, gut integrity. These shift how the long-standing pattern is currently expressing itself — someone who has run fast for thirty years can present as slow under sustained load. Where current function and the questionnaire disagree, current function governs the protocol until the constraint clears.

Four things distort the picture often enough to be worth naming. Each is a reason to treat a reading as provisional — and each is checkable.

HPA axis dysregulation
Sustained cortisol dysregulation flattens the markers that would otherwise describe current function, and — per Chapter 7 of the book — pushes the questionnaire toward sympathetic answers at the same time. That is the case where both instruments move together and neither is trustworthy. Address it first, then reassess.
Gut dysbiosis and permeability
Endotoxaemia from a permeable gut drives inflammation that suppresses anabolic signalling and distorts absorption. Someone whose reading calls for more protein and fat may not be absorbing or using it — which looks like the reading being wrong, when it is the gut. Evidence grade: mechanistic, with mixed human data on the downstream nutritional effect.
Nutrient cofactor depletions
Krebs cycle function requires B vitamins, magnesium, CoQ10 and iron. Depletion slows energy production regardless of position — a fast oxidiser runs functionally slow when cofactors are insufficient. This is why a reading taken before nutritional foundations are in place is worth less than one taken after.
Thyroid function
Thyroid hormone is the primary regulator of metabolic rate, and low function produces fatigue, weight gain and cold intolerance that look exactly like slow oxidation. Stated properly: laboratory upper reference limits for TSH differ between labs — commonly somewhere between 4.0 and 5.5 mIU/L — and no cut-off below a laboratory's own upper limit has been validated against clinical outcomes. A TSH in the upper part of the range is a reason to look harder, not a diagnosis, and we flag it as a possible confounder on that basis.
Now Available on Amazon
Metabolic Natures

Two axes. Six positions. A place to start.

The framework in full — the two axes and the six positions on them, what the functional tests do and do not tell you, the blocking factors that distort the picture, and the nutritional, supplemental and movement approaches that follow from a reading. Available in paperback and Kindle. Chapter 6 has a published correction, dated, and this site is authoritative where the two disagree.

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