New Study Shows Waist Circumference and Body Fat Tell the Real Story
Two people can weigh the same, have the same BMI, but be con be total opposite when it comes to their risk of chronic disease and death. This is a common scenario and something I see daily in my clinic. A new study on BMI shines a light on this phenomenon, uncovering that the weight you see on the scale is simply not helpful.
I’m going to review a study published in the Annals of Family Medicine in June 2025 by a team out of the University of Florida. The study design posed a great question: which measurement is a better predictor of health: BMI, waist circumference (WC), or body fat percentage (BF%)?
Understanding BMI, Waist Circumference, and Body Fat Percentage
Before we get into the meat of the article, let’s review some terms:
- Body Mass Index (BMI)
- a standardized assessment of body size using weight and height. BMI has been the gold standard definition of healthy weight vs overweight vs obesity in major trials.
- BMI <25 is “normal”; 25-30 is overweight; >30 is obese
- BMI is a good predictor of health when studying thousands of people, with higher BMIs correlating to worse chronic health outcomes.
- BMI is far less helpful at the individual level: we see many people labeled as obese by BMI who are in pristine health whereas others labeled as “normal” BMI with a lot of chronic medical conditions.
- Waist circumference (WC)
- Measurement of your abdominal circumference at the level of the navel.
- Larger WC correlates to increased visceral fat, a particularly unhealthy form of fat that surrounds and damages internal abdominal organs.
- Increasing WC is directly correlated to worsening metabolic health and is used in the diagnosis of Metabolic Syndrome.
- Healthy WC = <35in for women and <40in for men
- Body Fat Percentage (BF%)
- Precise measurement of body fat in pounds or kilograms, often using a DEXA machine
- Your weight is made up of body fat, lean mass (weight of muscle + water + organs), and bone. Weight loss or weight gain can be affected by changing any of these metrics.
- From a health perspective, the goal is to reduce body fat and/or gain lean mass, which you can only ascertain using a body composition scan.
- Healthy BF%: 25-31% for women and 18-24% for men
What’s the Best Way To Measure Body Fat?
Now onto the study. The study looked to determine any connection between BMI or WC or BF% and all-cause mortality and cardiovascular mortality over a 15-year period. All-cause mortality is on of the most meaningful ways to assess health impact. Basically, does this health change reduce our chance of dying for any reason? Cardiovascular mortality is assessing whether an intervention reduces the risk of dying from a heart attack or stroke.
Study Population:
4200 individuals within the NHANES database (a large database of collected US health information)
How they defined “Unhealthy”:
- BMI: ≥25 = overweight/obese
- WC: >40″ for men; >35″ for women
- BF%: ≥27% in men, ≥44% in women
Here’s what they found:
- BMI: No correlation at all
- WC: 59% higher risk of death, 4x (300%) higher cardiovascular risk
- BF%: 78% higher risk of death, 3.6x (262%) higher cardiovascular risk
BMI had zero correlation to all-cause mortality or cardiovascular mortality over 15 years. But there was a HUGE correlation using WC or BF%. BF% is the best predictor of all-cause mortality, the health metric that really matters.
And if you do not have access to a DEXA machine, waist circumference is also a great tool.
Body Fat and Poor Health Outcomes
Excess body fat, especially excess body fat around the midsection (i.e. visceral fat), is a major driver of most chronic medical conditions: cancer, diabetes, heart attacks, strokes, dementia, and autoimmune conditions. Visceral fat is particularly inflammatory, damages organs, and disrupts the body’s ability to heal, create energy, and function at its best. The best way to really know if you have excess body fat is to measure this directly: waist circumference and body composition scan (which measures visceral fat + fat found elsewhere).
When you step on a scale, you are seeing a sum of body fat, lean mass, and bone. If your weight is changing, a scale cannot tell you what exactly is changing in your body. Is it fat? Is it muscle? Is it water? Since BMI is only based on weight, it fails to be a truly accurate measurement for health.
From a health perspective, focusing on reducing body fat to healthy ranges while also increasing lean mass to healthy ranges is the best strategy to experience your best state of health.
Body Composition Scans as a Health Vital Sign
Though we’ve been recommending this for years, this study gives us more data to back up our claims: if you really care about your health, get a body composition scan at least once per year (or 2-3 times per year if losing/gaining weight) and monitor your waist circumference as often as you like. Body fat percentage or waist circumference should be treated like vital signs and closely tracked over time.
Schedule a Body Composition Scan in Asheville, NC
To learn more about body composition scans at our office, click here. If you don’t live near Asheville, a quick internet search can likely find an option near you. r personalized care strategies might be right for you.