Pulse ·

Your BMI is normal — but you could still be clinically obese

By Dr HB Lo, FACRRM 4 min read
Verdict Yes — worth knowing about

Body mass index (BMI) is a population screening tool, not an individual diagnostic. New research shows 26% of adults with a normal BMI still meet criteria for clinical obesity when broader adiposity measures are applied.

BMI cannot detect visceral fat stored around the abdominal organs, which drives metabolic and cardiovascular risk. Perimenopausal fat redistribution can increase visceral fat substantially without any change in weight or BMI.

A normal BMI is not a complete metabolic clearance. Waist circumference, waist-to-height ratio, and a fasting metabolic panel add context that BMI alone cannot provide.

What just happened

The Medical Republic ran a GP-focused piece this week on research that will not surprise many women in their 40s — but that should change how their results are interpreted. A study of over 5,600 US adults, published in the Annals of Internal Medicine and using data from the 2021-2023 National Health and Nutrition Examination Survey (NHANES), found that 26.1% of adults with a body mass index in the normal range still met criteria for clinical obesity when assessed against broader anthropometric measures.

One in four. Normal BMI. Clinical obesity.

The study participants had a mean weighted age of 48.7 years — right in the middle of the perimenopausal window for women. The clinical obesity definition applied was drawn from the Lancet Commission’s updated framework, which moves beyond BMI to include waist circumference, waist-to-height ratio, and physiological signs that excess adipose tissue is generating metabolic stress in organs.

This matters in Australian general practice not as a headline scare but as a long-overdue correction to a clinical shorthand. Many women arrive at a GP appointment having been told for years that their weight is within the normal range. The Medical Republic piece is part of a broader movement in clinical medicine to retire BMI as the sole diagnostic lever — and to acknowledge what many patients have suspected for some time.

The both-and

BMI is a useful tool — within its original limits

Body mass index is not a fraud. It is a quick, costless, no-equipment screening tool that correlates reasonably well with body fat at the population level. The Australian Institute of Health and Welfare uses BMI as a primary metric when tracking national trends in overweight and obesity — and for that purpose, it is fit for purpose. Population-level surveillance is exactly what BMI was designed to do.

The problem is not BMI itself; it is what BMI was never designed to do. It cannot distinguish fat from muscle. It cannot tell us where fat is distributed. It cannot capture the difference between subcutaneous fat — stored under the skin, which is metabolically relatively inert — and visceral fat, which wraps around the abdominal organs and actively drives insulin resistance, inflammation, and cardiovascular risk.

At a BMI of 23.5, one woman may have no visceral fat and excellent metabolic markers. Another woman at the same BMI, navigating perimenopause, may have significant central fat redistribution, a waist circumference above the Australian evidence-based threshold of 80 cm, and blood glucose quietly creeping toward the pre-diabetic range. BMI reports them identically.

The perimenopausal problem with “normal weight”

This is where the research hits differently for women in midlife. Oestrogen plays a role in fat distribution. As oestrogen levels decline during the perimenopausal transition — a process that can span a decade — the body’s fat storage pattern shifts. Subcutaneous fat, which oestrogen preferentially supports in the hips and thighs, migrates toward the abdomen. Central and visceral fat increases. This can happen in the absence of any meaningful change in total body weight or BMI.

The NHANES dataset underlying this week’s Annals of Internal Medicine study had a mean participant age of 48.7 years. The 26.1% of normal-BMI adults found to meet criteria for clinical obesity were not outliers. They were, in many cases, precisely the demographic that sits in a general practice consulting room being told their weight is fine — while their waist circumference, lipid profile, and blood glucose tell a different story.

The Lancet Commission’s updated definition of clinical obesity requires abnormal anthropometric measures or evidence of adiposity-related organ impairment. Its purpose is not to classify more people as obese for its own sake. It is to surface the people whose risk profile is being missed by a number on the scales.

2 cents

If your BMI is normal but you carry weight around your abdomen, your waist measures more than 80 cm, and you have noticed fatigue or blood glucose results changing at recent health checks — the tools being used to assess your metabolic health are worth revisiting.

The relevant additions to BMI are not complicated. Waist circumference, waist-to-height ratio (below 0.5 is the current evidence-based threshold for lower metabolic risk), and a fasting lipid and glucose panel give your GP a substantially richer picture than weight and height alone. These are standard general practice investigations.

The conversation worth raising at your next appointment is not “I think I have clinical obesity.” It is: “My weight is stable, but I would like to understand whether my metabolic health is being assessed fully — beyond BMI.”

Verdict: yes — this research updates a clinical shorthand that has been leaving real metabolic risk undetected for too long.

Sources cited

  1. Medical Republic — A normal BMI doesn’t mean you aren’t clinically obese. 7 July 2026. https://www.medicalrepublic.com.au/a-normal-bmi-doesnt-mean-you-arent-clinically-obese/127029
  2. Annals of Internal Medicine — Clinical obesity prevalence study using NHANES 2021-2023 data. Published 2 June 2026. https://www.acpjournals.org/journal/aim
  3. AIHW — Overweight and obesity in Australia. https://www.aihw.gov.au

Frequently asked questions

  • What is clinical obesity and how is it different from BMI-based obesity?

    Clinical obesity is defined by the physiological consequences of excess fat — including waist circumference, waist-to-height ratio, and signs of organ stress from adipose tissue — rather than BMI alone. BMI measures weight relative to height but cannot tell us where fat is stored. Visceral fat, stored around the abdominal organs, carries more metabolic risk than subcutaneous fat — and BMI misses this distinction entirely.

  • Does this mean BMI is useless?

    No — BMI remains a useful quick screen at the population level. The problem is treating it as a definitive individual diagnostic. A 45-year-old woman can have a normal BMI while carrying significant central adiposity and elevated metabolic risk, particularly during perimenopause when fat redistributes even without meaningful weight change.