The normal-weight person with a metabolic problem

Picture someone who clears every box on the standard health check: BMI 23, no obvious symptoms, told everything looks normal. On paper, they are fine. In their blood, something different may be unfolding.

Roughly one in five normal-weight adults belongs to a category researchers call metabolically obese normal weight — MONW for short. These individuals carry excess visceral fat and impaired metabolic function despite a healthy-looking weight-to-height ratio. Studies suggest this group faces more than three times the cardiovascular and mortality risk of metabolically healthy people at an identical BMI.

A blood panel separates them immediately. In a 2015 characterisation study, metabolically unhealthy normal-weight adults showed mean HbA1c of 6.1% against 5.3% in their healthy counterparts — a difference that flags glucose dysregulation well before diabetes is diagnosed. Triglycerides told the same story: 1.47 mmol/L versus 1.11 mmol/L. Both gaps are clinically meaningful and both are invisible to BMI, because BMI is a ratio of weight to height squared. It has no biochemical substrate; it simply cannot see inside.

This is not a statistical quirk at the edges of a bell curve. It is a structural limitation of what BMI was designed to do — track population-level body size in 19th-century France, not assess the internal chemistry of any individual alive today.

Which raises the obvious question: your BMI may be fine, but what is actually happening in your blood?

BMI as a 19th-century tool in a 21st-century body

The gaps Professor Paul Lee identifies go beyond the familiar complaint about muscular athletes registering as overweight. In Practical Regeneration (February 2026), his follow-up to the Amazon #1 bestselling Regeneration by Design, he sets out three specific blind spots: BMI says nothing about bone density, it cannot account for ethnic variation in metabolic risk — the same number may mean quite different things depending on an individual's ancestry and body composition — and it offers no window whatsoever into the body's biochemistry. A lean person and someone who has lost substantial muscle mass through inactivity can sit at identical BMI values while their internal states diverge completely.

These are not measurement errors; they are category errors. BMI was designed to count bodies at population scale, not to interrogate any individual body's chemistry. What it cannot see is precisely what matters most for healthspan.

Lee's Regeneration by Design addresses this directly through its Chemistry pillar — one of four interdependent pillars that form the basis of the Regen PhD approach. Chemistry covers nutrition, hormones, inflammation, and what Lee calls the body's internal environment: the living, shifting biochemical landscape that determines how well the body repairs, regulates, and regenerates. Unlike a weight-to-height ratio, that landscape is directly readable. Blood markers respond to what a person eats, how they sleep, how they manage stress. They can be tracked, compared against established thresholds, and acted upon. For anyone genuinely trying to design their healthspan rather than simply monitor their silhouette, that is where the real signal lies.

The metabolic layer — glucose, insulin, and fat signals

A fasting blood draw captures the body's chemistry before a meal triggers compensatory responses — and three clusters of markers reveal what is actually happening in the glucose-insulin axis and the fat-handling system.

Glucose and HbA1c measure the same problem at different time horizons. Fasting glucose reflects the moment; a healthy value sits below 100 mg/dL (5.6 mmol/L). HbA1c shows the average blood-sugar level over the preceding two to three months by measuring how much glucose has bonded to haemoglobin in red blood cells. A reading below 5.7% indicates the body is managing sugar well; values creeping toward 6.0% suggest the regulatory system is straining — often years before a formal diagnosis appears.

HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) uses fasting glucose and fasting insulin together to calculate how hard the pancreas is working to keep blood sugar stable. It is one of the few routine ways to detect early insulin resistance — a state where cells become progressively less responsive to insulin's signal — without a specialist clinical test. A weight-to-height ratio cannot estimate it.

Triglycerides and HDL cholesterol reflect how efficiently the body is clearing fat from the bloodstream. The ratio between them — TG divided by HDL — is widely used as a practical proxy for insulin resistance: a high ratio may suggest fat is accumulating where it should not be.

Together these markers form a metabolic fingerprint: individual, responsive to lifestyle choices, and measurable across time. A fingerprint can be tracked against a personal baseline and meaningfully shifted — which is precisely what makes it useful for anyone actively designing their healthspan rather than simply monitoring their weight.

Visceral fat, inflammation, and the markers that see what scales cannot

Most people think of body fat as inert — stored energy sitting beneath the skin. Visceral fat, the fat wrapped around the organs deep in the abdominal cavity, behaves entirely differently. It functions as a metabolically active secretory tissue, releasing pro-inflammatory cytokines — including IL-6 and TNF-α — directly into the bloodstream. The result is chronic low-grade inflammation that suppresses insulin sensitivity and gradually undermines the body's capacity to repair itself. A set of scales detects none of this.

Several blood markers reflect this burden directly. High-sensitivity CRP (hs-CRP) rises as the liver responds to circulating IL-6. The adipokines — leptin and adiponectin — are produced by fat tissue itself and shift in opposite directions as visceral fat accumulates: leptin climbs (amplifying appetite dysregulation and inflammatory signalling), while adiponectin falls (removing a key anti-inflammatory, insulin-sensitising brake). A 2021 study in 196 women found that hs-CRP, IL-6, leptin, adiponectin, triglycerides, HDL, and insulin all correlated with molecular-level tissue changes linked to disease pathogenesis — confirming that these markers carry genuine mechanistic signal, not just population-level noise.

The leptin-to-adiponectin balance deserves particular attention: a widening gap between the two is associated with accelerating metabolic decline even when body weight stays flat.

A 2025 MDPI study makes the BMI contrast precise: a diverse inflammatory biomarker panel showed no straightforward association with BMI-calibrated obesity in clinically healthy adults. BMI cannot reliably proxy internal inflammatory status — not even at group level.

This is the 'internal environment' Lee describes in Regeneration by Design — the body's background chemistry that either supports regenerative processes or quietly erodes them. Tracking it directly, rather than inferring it from a weight-to-height ratio, moves assessment from approximate to actionable, and gives anyone serious about their healthspan a genuine read on what is happening beneath the surface.

The wider panel — cardiovascular signals and sex-specific differences

Beyond metabolism and inflammation, a complete panel adds two further layers that BMI cannot begin to address: cardiovascular risk architecture and organ function.

Cholesterol and atherogenic burden. Standard lipid panels report LDL cholesterol as a weight of cholesterol in the blood. ApoB (apolipoprotein B) is more informative: each LDL particle carries exactly one ApoB molecule, making the ApoB count a direct measure of atherogenic particle number — regardless of how much cholesterol each particle happens to carry. Two people with identical LDL readings can have very different ApoB counts, and the higher count carries greater arterial risk. BMI offers no information on either figure.

Organ-function signals. ALT and AST (liver enzymes) and uric acid extend the picture further. Elevated ALT is among the earliest biochemical signs of metabolic liver stress — it can rise years before any weight change or visible symptom, making it a genuinely early-warning marker. Uric acid reflects purine metabolism and is associated with insulin resistance at levels once considered unremarkable.

Sex matters at the panel level. A 2025 comparative study analysing plasma concentrations of more than 90 biomarkers found meaningful sex-stratified differences in inflammatory and metabolic markers within the same BMI categories. The same reading can conceal very different internal chemistry depending on sex — a nuance that a population-level ratio cannot express but a panel, interpreted in context, can.

For the 40–70+ reader, hormonal status — DHEA-S, testosterone, IGF-1 — adds a longevity dimension that sits beyond the standard metabolic and cardiovascular panel. Each reflects biological age and regenerative capacity in ways no weight-derived metric can approach. The evidence linking them to structured healthspan protocols is still developing, but they represent a natural next step for anyone ready to go further than the metabolic baseline.

From numbers to action — making your panel work for you

Getting a panel is simpler than many people assume. A GP or private clinic can run a comprehensive metabolic panel, lipid panel with ApoB, hs-CRP, and fasting insulin alongside a full blood count — the starting toolkit for understanding the internal environment. The first result is not a verdict; it is a baseline. The real value accumulates over time as trends become visible: inflammation quietening after dietary changes, the glucose-insulin axis responding to sleep improvements, the leptin-to-adiponectin balance shifting as body composition is actively managed.

This is where the Chemistry pillar connects to the rest of what Professor Paul Lee sets out in Regeneration by Design. Better internal chemistry supports better Physics — tissue repair and physical recovery both depend on a low-inflammation substrate. It feeds Biology too: the gut, the immune system, and sleep architecture all run more efficiently when metabolic and inflammatory load is reduced. One reading tells you where you are; serial readings, tracked against what you are changing, reveal whether the system is actually responding.

The practical aim, then, is to move from a static number on a scale to a living read of the body's chemistry — a picture that changes as you change, and that gives your decisions somewhere to land. That is what it means to design a healthspan rather than wait for it to arrive.

This article is for general educational purposes only. It does not constitute medical advice. Please discuss any blood test results or health concerns with a qualified healthcare professional.

1. [1] Body mass index — Wikipedia. https://en.wikipedia.org/?curid=4788 https://en.wikipedia.org/?curid=4788