An American study revealed that about 26% of people with a normal body mass index suffer from clinical obesity according to new medical standards, meaning that millions may not receive the appropriate treatment for their condition.
The study was conducted by researchers from the University of Southern California, led by Dr. Brian Lee, a liver specialist at the Keck Center for Medicine.
The team analyzed data from the National Health and Nutrition Examination Survey (NHANES), a nationally representative survey conducted by the U.S. Centers for Disease Control and Prevention.
The researchers focused on a group of middle-aged people who underwent comprehensive examinations in addition to measuring body mass index, such as measuring waist circumference, hip circumference, waist-to-hip ratio and waist-to-height ratio.
The study is based on new standards for measuring obesity developed by a large team of obesity experts around the world in January 2025, with support from The Lancet.
The new standards do not completely abandon the body mass index, but they add other measurements such as waist circumference and DEXA scan (a test that measures bone density and body fat percentage).
The criteria also distinguish between two stages of obesity:
Clinical obesity: The presence of obesity that causes actual harm to health, such as tissue damage or obesity-related diseases such as high cholesterol, type 2 diabetes, or chronic knee pain.
Preclinical obesity: The presence of excess fat without associated health problems so far.
Researchers found that 78% of Americans are considered obese according to the new criteria. Even more striking is that approximately 26% of people with a normal body mass index (BMI) (between 20 and 25) met the definition of clinical obesity, while more than 50% of those considered overweight (BMI between 25 and 30) met the same definition.
calculated using only weight and height, and classically classifies obesity as having a BMI over 30. However, experts argue that this definition is inaccurate because obesity is fundamentally linked to the amount of excess body fat, not just weight and height.
A thin person may have excess fat that the scale does not show, and a tall person or one with large muscles may be classified as obese even though their body fat percentage is normal.
Researchers point out that relying solely on body mass index means that millions of people with clinical obesity go undiagnosed and therefore do not receive appropriate medical care.
Dr. Brian Lee explains: "Because most doctors focus on BMI to screen for obesity-related conditions, this group of people may not receive enough attention for screening and treatment."
Effective treatments such as GLP-1 drugs (Ozempic and Govovi) and gastric bypass surgery are currently limited to those who meet the classic criteria for obesity (BMI 30 or higher). There are still insufficient studies on the effectiveness of these treatments for people with a normal BMI who have excess body fat.
Lee adds: "The important question is whether treating excess fat in people with a normal body mass index can reduce obesity-related health conditions. We need prospective studies and randomized clinical trials to answer this question
Researchers advise against relying solely on body mass index (BMI). Dr. Lee says, "Using a measuring tape to measure your waist, hips, and height is an easy way to determine if you have excess fat that could be detrimental to your health."
The results were published in the Annals of Internal Medicine.
