There has been a long push to replace BMI with something better. Various successors have been proposed — body roundness index, multi-measurement frameworks, imaging-based definitions. A study published in JAMA Network Open in August 2026 tested whether the complexity actually buys anything.
It largely does not. A tape measure did about as well.
What the study found
Researchers at Rutgers Health compared several approaches to identifying unhealthy body fat. Their finding: combining BMI with waist circumference — or using waist circumference alone — performed as well as a newly proposed obesity definition incorporating multiple body measurements.
They also found that BMI on its own missed a substantial number of people who met body-fat criteria for obesity.
That second point is the important one, and it is not new so much as newly confirmed. BMI cannot distinguish muscle from fat and cannot see where fat is stored. Both limitations have been understood for years; what keeps changing is how much they are shown to matter.
What we found in the same national data
We ran a related question ourselves against the CDC’s NHANES 2021–2023 survey, and the results line up.
Among 5,745 US adults, applying survey weights, strata and primary sampling units:
- 47.0% (95% CI 42.5–51.5) of adults with a BMI in the healthy range of 18.5–24.9 had a waist-to-height ratio of 0.5 or above — roughly 28.7 million American adults
- By age: 22.5% at 20–39, 54.4% at 40–59, 75.5% at 60 and over — within the same BMI band
- Across all adults, BMI classified 40.0% as obese while an elevated waist-to-height ratio flagged 82.9%
Our BMI figure of 40.0% closely matches the CDC’s own published estimate for that period, which is how we checked that the survey weighting was behaving correctly. Full method and confidence intervals are in the complete analysis, and the figures are free to cite.
The caveat we would rather state than bury
That 42.9-percentage-point gap between the two definitions is not simply BMI failing. It also reflects the waist threshold being deliberately sensitive.
When a marker flags four out of five adults in a country, it is describing a risk gradient rather than diagnosing a disease. A ratio of 0.51 is not meaningfully different from 0.49. Anyone presenting the waist measurement as a precise diagnostic replacement for BMI is overstating what it does.
The honest framing is that both measures are screening tools with different blind spots, and using them together is better than either alone — which is essentially what the Rutgers study concluded.
How to measure it correctly
Most people do this wrong, and the error is always in the same direction.
Measure at the top of your hip bones — the iliac crest — not at your natural waist or narrowest point. Do it at the end of a normal exhale. Keep the tape snug without compressing the skin. Do not hold your breath or pull your stomach in.
Then divide by your height in the same units. Under 0.5 is the general target: your waist should be less than half your height. Our free calculator does the arithmetic.
One important qualification: the 0.5 threshold is applied uniformly, but body fat distribution at a given waist size genuinely differs by ancestry. Several bodies recommend lower thresholds for people of South and East Asian descent, meaning standard screening likely under-detects risk in those groups.
What to do if you are above it
An elevated ratio with a normal BMI is not a diagnosis — it is a reason to get three specific tests that a normal BMI often prevents anyone from ordering: a fasting glucose or A1C, a lipid panel, and a blood pressure reading. Those, plus your waist, are four of the five criteria for metabolic syndrome.
The response is mostly not weight loss, because there may be little excess weight. It is resistance training and adequate protein to build the muscle that sets your metabolic floor (why this pattern matters, and how much protein). Visceral fat is metabolically active and tends to respond early, which is why the tape often moves before the scale does (what works).
When to see a doctor
Ask for an A1C or fasting glucose, a lipid panel and a blood pressure check if your waist-to-height ratio is 0.5 or above — and say so explicitly, because a normal BMI can end that conversation before the tests are ordered. This matters more with a family history of type 2 diabetes or early heart disease.
See a doctor about rapid waist increase without weight gain, or abdominal swelling that develops over weeks, which needs a different evaluation entirely.
The honest bottom line
A new JAMA Network Open study found that a waist measurement performs about as well as elaborate multi-measurement obesity definitions, and that BMI alone misses many people carrying obesity-level body fat. Our own analysis of the CDC’s national survey found the same gap from the other direction: 47% of adults with a healthy BMI have an elevated waist-to-height ratio. The tape measure is not a better diagnostic — it is a sensitive screen that sees something the scale cannot. Use both.
Frequently asked questions
Is waist circumference better than BMI?
For detecting unhealthy body fat, it captures something BMI cannot — where fat is stored. A JAMA Network Open study in August 2026 found waist circumference performed as well as elaborate multi-measurement obesity definitions, and that BMI alone missed many people with obesity-level body fat. But waist thresholds are deliberately sensitive screening cut-offs rather than diagnostic tests, so the practical answer is to use both rather than replacing one with the other.
How do you measure waist-to-height ratio correctly?
Measure your waist at the top of your hip bones, at the end of a normal exhale, with the tape snug but not compressing the skin. Do not measure at the narrowest point, do not hold your breath, and do not pull your stomach in. Then divide the waist measurement by your height in the same units. Under 0.5 is the general target — your waist should be less than half your height.
Can you have a normal BMI and still be unhealthy?
Yes. Our analysis of NHANES 2021–2023 found that 47% of US adults with a BMI in the healthy range of 18.5 to 24.9 had a waist-to-height ratio of 0.5 or above — roughly 28.7 million people. The pattern rose sharply with age, from 22.5% at ages 20 to 39 up to 75.5% at 60 and over, within the same BMI band. A normal BMI is weaker reassurance than most people assume, particularly after 40.