For decades, body mass index (BMI) has been the standard tool doctors use to determine whether someone is overweight or obese. But new research suggests that the familiar calculation may be overlooking millions of Americans who are already experiencing obesity-related health problems.
A study published in the Annals of Internal Medicine found that obesity rates in the United States could be significantly higher than BMI estimates suggest. Researchers discovered that about one in four adults classified as having a healthy BMI actually met the criteria for obesity under a newer medical definition known as clinical obesity.
The findings add to growing concerns among health experts that BMI alone may not provide an accurate picture of a person’s weight-related health risks.
“Many people assume that if their BMI says they are not obese, they don’t have to worry about the many health problems linked to obesity,” said principal investigator of the study Brian P. Lee in a press release. “Our findings show that millions of Americans may already have obesity-related health impacts and may be missing needed health interventions.”
New Obesity Definition Reveals Hidden Health Risks
To better understand how often BMI may fail to identify obesity, researchers analyzed data from approximately 5,600 adults who participated in the National Health and Nutrition Examination Survey. They measured participants’ BMI and body fat distribution, including waist and hip circumference.
When researchers compared traditional BMI classifications with clinical obesity criteria, they found substantial differences. About 26 percent of adults with a healthy BMI qualified as clinically obese, while roughly 50 percent of those categorized as overweight also met the definition.
These findings highlight a growing shift in how obesity is being understood. Rather than focusing solely on body weight, researchers and clinicians are increasingly examining where fat is stored in the body and whether it is causing health problems.
BMI vs. Clinical Obesity: What Is the Difference?
Doctors calculate BMI using a person’s height and weight and place individuals into categories ranging from underweight to obese. While the tool is simple and inexpensive, it has limitations.
“BMI is problematic because it does not specifically measure body fat and instead reflects total body weight, which includes muscle and bone. So a muscular person can have a very high BMI but not have excess fat, while someone without much muscle can have a normal BMI but have excess fat causing health problems,” explained Lee.
The Lancet Diabetes and Endocrinology Commission introduced the newer concept of clinical obesity in 2025. Instead of relying on weight alone, it focuses on abdominal fat, sometimes called adipose fat, which accumulates around internal organs and can trigger inflammation throughout the body.
Doctors assess clinical obesity by using three measurements: waist circumference, waist-to-hip ratio, and waist-to-height ratio. If at least two of these measurements indicate excess abdominal fat and the person has obesity-related health issues, they may be diagnosed with clinical obesity.
Why Accurate Obesity Diagnoses Matter
The distinction is more than a medical technicality. Research links obesity to serious conditions including heart disease, Type 2 diabetes, high blood pressure, liver disease, elevated cholesterol, and several forms of cancer.
Because many treatment guidelines still rely heavily on BMI, people with clinically significant obesity but normal BMI may not qualify for medications, surgery, or other interventions that could improve their health outcomes. They may also miss opportunities for earlier lifestyle changes that could reduce future risks.
Researchers hope the findings encourage more healthcare providers to adopt the clinical obesity framework and move beyond BMI alone when evaluating patients.
“The good news is that obesity can be treated. Whether through lifestyle changes, medication or both, we have effective ways to reduce excess body fat and lower the risk of future health problems. The earlier we identify people at risk, the better chance we have of improving long-term health and quality of life,” concluded Lee.
This article is not offering medical advice and should be used for informational purposes only.
Read More: Calorie Counting and 10,000 Steps a Day — How Closely Should You Follow These 5 Health Goals?
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in the Annals of Internal Medicine: National Prevalence of Clinical Obesity by BMI Class: A National Cross-Sectional Study
