Why BMI Was Never Designed for You

Your last blood panel came back fine. Your doctor glanced at your height and weight, pronounced your BMI normal, and moved on. Yet your energy has been sluggish for months, your body composition feels wrong, and recovery after exercise takes longer than it should. If that gap between the number and the reality feels familiar, there is a structural reason for it — one that dates back nearly two centuries.

BMI was not invented by a clinician. In 1832, Adolphe Quetelet — a Belgian mathematician and statistician best known for founding the Brussels Observatory — developed the formula to describe what he called the l'homme moyen, the 'average man', for population-level statistical modelling. It was a tool for counting, not for clinical assessment. Quetelet never intended it to evaluate individual health, body fat, or disease risk, and the reference data he drew from was derived exclusively from European white males — an assumption quietly embedded in every reading since.

The formula sat largely outside medicine for well over a century. It was not adopted clinically until the 1970s, and the cut-offs most people still recognise — 'overweight' at 25, 'obese' at 30 — were standardised only in 1998, when the US National Institutes of Health aligned with WHO thresholds. Millions of people were reclassified as overweight overnight, without a single biological change.

Peer-reviewed consensus has caught up with this history. A 2024 PMC review by Wu et al. and a 2023 clinical analysis by Muscogiuri et al. both conclude that BMI functions as a useful population-screening shorthand but is poorly suited to predicting individual chronic disease risk or assessing excess fat with any precision.

The Chemistry pillar in Professor Paul Lee's Regeneration by Design framework rests on reading the body's internal environment accurately. That environment — hormones, metabolic signals, inflammatory load — is invisible to a number derived from height and weight. BMI describes a population. It says very little about you.

What a Scale Number Cannot See

Two people can share an identical BMI of 24 — both classified 'healthy' — while their bodies are doing entirely different things. One may carry lean muscle built from years of consistent training; the other may have low muscle mass and a substantial accumulation of fat gathered silently around the organs. The formula registers both as the same.

Muscle and fat are metabolically opposite. Muscle is active tissue that draws on glucose and supports insulin sensitivity. Visceral fat — stored around the liver, pancreas and intestines — behaves less like a storage depot and more like a broadcasting organ, continuously releasing free fatty acids and inflammatory proteins directly into the portal circulation. Those signals nudge the liver towards insulin resistance and push lipid profiles in an atherogenic direction. A height-and-weight ratio captures none of this.

This is where the normal-weight central obesity finding becomes the sharpest challenge to BMI's authority. Research published in BMJ Open in 2017, and confirmed by a 2025 Springer study, found that up to one in five adults with a BMI in the healthy range carries excess visceral fat — and that their cardiometabolic risk is comparable to, or in some cases exceeds, that of individuals formally classified as overweight. 'Skinny fat' is not an aesthetic concern; it describes a metabolic state that weight-based screening misses entirely.

Waist circumference offers one practical first step — measurements above 80 cm in women or 94 cm in men signal central fat accumulation that BMI would never flag. Yet even that measurement stops at the body's surface. What the visceral fat is actually releasing into circulation, and how far that process has already progressed, is a question only the bloodstream can answer.

The Four Blood Markers Worth Knowing

Four markers come up repeatedly in longevity medicine as the precision tools that BMI cannot replicate — each answering a distinct question about what is unfolding inside the body.

Fasting insulin asks: how efficiently is the body managing its fuel? Insulin rises when cells begin to resist its signal, and the pancreas compensates by producing more. That compensatory rise is detectable in a fasting blood draw an estimated 10 to 15 years before glucose levels cross any threshold of clinical concern. It is one of the earliest readable signals of a metabolic process already in motion.

ApoB asks: what is actually building up in the vessel walls? A standard lipid panel measures cholesterol mass — specifically LDL-C. ApoB counts the total number of atherogenic lipoprotein particles circulating in the blood, each capable of embedding in arterial tissue. It is a more direct indicator of cardiovascular risk than the cholesterol content those particles happen to carry.

HbA1c asks: what has the average glycaemic load been doing over the past 8 to 12 weeks? Haemoglobin binds irreversibly to glucose; the proportion that is glycated reflects sustained blood sugar rather than a single-morning snapshot. Prolonged elevation accelerates the formation of Advanced Glycation End-products — AGEs — that stiffen connective tissue and are implicated in both cardiovascular and cognitive ageing.

hs-CRP asks: how much inflammation is running silently in the background? High-sensitivity C-reactive protein is produced by the liver in response to inflammatory signalling elsewhere in the body. Chronic low-grade elevation often produces no felt symptom, yet the research consistently links it to accelerated biological ageing and the same insulin resistance and vascular risk mapped by the other three markers.

Read together, these four markers trace the internal chemistry that Professor Paul Lee describes in Regeneration by Design as the body's most legible environment — the one that determines how well every other biological process is running, and the one that a height-and-weight ratio will never reach. What matters is not simply whether any single result falls within a 'normal' reference range, but where it sits relative to the levels associated with sustained long-term function — a distinction worth examining in some detail.

The Gap Between 'Normal' and Optimal

Passing a reference range and thriving within it are not the same thing. The thresholds printed on a standard blood report are calibrated to identify disease — they tell a clinician where population averages tip into clinical concern, not where a given person's markers need to sit to sustain decade-long vitality.

Think of it as the difference between a car engine running 'within spec' and running cleanly. The engine may pass its diagnostic check at every service while quietly accumulating wear that a more precise reading would catch years earlier.

The numbers illustrate the gap precisely. The conventional reference for fasting insulin sits below 10 μIU/mL; longevity medicine tends to work towards 2–5 μIU/mL — the zone where insulin sensitivity is genuinely intact rather than merely compensated. For ApoB, standard panels may accept anything below 90–100 mg/dL; the longevity-medicine target is below 80 mg/dL. HbA1c has a conventional alert threshold of 5.7%; the longevity-optimal window sits between 4.8 and 5.2%. For hs-CRP, true chronic-inflammation control may mean below 1.0 mg/L, rather than the standard clinical alert level of 3.0 mg/L.

Someone can receive an entirely unremarkable set of results — 'all normal' — while carrying years of low-grade metabolic or inflammatory burden that a tighter reading would surface. That is the gap where preventable decline quietly accumulates.

These narrower targets reflect emerging practice in longevity medicine rather than universal clinical guidelines, and they are best explored with a qualified clinician rather than self-prescribed. What they represent, as the framework in Regeneration by Design makes clear, is the difference between monitoring for illness and actively designing for function — a distinction that a height-and-weight ratio cannot begin to approach.

What Centenarians' Blood Showed Decades Earlier

The most direct evidence that biomarkers function as a long-range forecast comes from the Swedish AMORIS cohort — a 35-year study of more than 1,200 people who reached their hundredth birthday, published by Murata and colleagues in 2023.

What the researchers found was not a genetic lottery. Compared with individuals who died before the age of 100, the centenarians consistently displayed more favourable blood profiles from their mid-sixties onwards — measurably lower glucose, creatinine, uric acid, and liver enzymes including AST and GGT. Notably, higher total cholesterol and iron also featured in the centenarian group, a finding that complicates any single-marker story. The divergence between the groups was not concentrated in the final years of life; it was already visible at an age when most people receive 'all normal' results and ask nothing further.

The data supports a particular conclusion about monitoring: a single blood draw captures a position; a series taken across years captures a direction. It was trajectory — established through the sixties, sustained into the seventies — that separated the two groups, not any single alarming result at a late stage.

This is the Time pillar expressed in the clearest possible terms. Tracking glucose, creatinine, and liver markers longitudinally matters less for what any individual reading shows than for the sustained drift it may reveal — the slow movement in one direction that a one-off check cannot see and that, caught early, remains correctable.

Building Your Baseline: What to Do This Month

Getting started is more straightforward than the science might suggest. Four markers form a sensible minimum: fasting insulin, ApoB, HbA1c, and hs-CRP. None is exotic — all four can be requested through a GP or a private testing service — though standard NHS checks do not routinely include all of them, particularly ApoB and hs-CRP.

Breadth matters when selecting a panel. Inflammation, metabolic function, hormonal balance, cellular energy, cardiovascular risk, and liver and renal health each capture a different dimension of how the body is functioning — a principle central to Professor Paul Lee's Regeneration by Design, which treats the body as a set of interdependent systems rather than isolated readings. Structured panels that span these areas may surface patterns a narrower check would miss; the Regen PhD Blood Panel, built around this approach, covers 32 markers across those six categories, including HOMA-IR and Lp(a).

One result in isolation has limited value. What separated the Swedish centenarians from the rest was not a single alarming reading but a direction held across decades. Tracking the same markers annually — watching whether fasting insulin is drifting upward, whether hs-CRP is quietly rising — is more informative than any single draw, however comprehensive.

Blood data also works best alongside simple physical measures: waist circumference, grip strength, and walking pace each add context that no blood test alone can provide.

Whatever a panel returns, the most useful next step is a conversation with a qualified healthcare professional who can interpret the numbers in the context of a full health picture. These markers are a more specific starting point for that conversation — not a route to self-diagnosis, but a set of sharper questions worth arriving with.

1. [1] Body mass index — Wikipedia. https://en.wikipedia.org/?curid=4788 https://en.wikipedia.org/?curid=4788
2. [2] Adolphe Quetelet — Wikipedia. https://en.wikipedia.org/?curid=184215 https://en.wikipedia.org/?curid=184215