Half of Overweight Americans May Actually Have Obesity, Study Finds

A new study is challenging one of the most basic tools doctors use to measure body weight. The results suggest that BMI has been getting it wrong for millions of Americans.

Researchers at Keck Medicine of the University of Southern California published the study on June 1, 2026, in the Annals of Internal Medicine. They examined data from over 5,600 adults and uncovered a pattern that is hard to ignore.

Among people with a normal BMI reading, one in four actually had obesity by clinical standards. Among those carrying an overweight label, the number climbed even higher. Half of them actually qualified as having obesity. That gap between what BMI shows and what exists inside the body is significant.

So why does BMI fall short? The answer comes down to what it actually measures. BMI only looks at weight in relation to height. It has no way of telling fat apart from muscle. A person who works out regularly and carries a lot of muscle could get flagged as overweight. At the same time, someone with a slim frame could carry dangerous levels of fat around their organs with no warning sign showing up on the scale.

Brian P. Lee, MD, the lead researcher on the study, put it plainly. “Many people assume that if their BMI says they are not obese, they don’t have to worry,” he said. “Our findings show that millions of Americans may already have obesity-related health impacts and may be missing needed interventions.”

That is where waist-to-hip ratio, or WHR, comes in. Instead of looking at total weight, WHR measures where fat sits on the body. Fat that builds up around the abdomen causes far more harm than fat stored around the hips or thighs. It wraps around internal organs, disrupts the body’s normal functions, and raises the risk of serious illness over time.

A 2023 study in JAMA Network Open backed this up. Researchers found that WHR carried the strongest link to the risk of dying from any cause, regardless of a person’s BMI. The takeaway was clear: where fat sits on the body matters more than total body weight.

Dan Azagury, MD, a surgery professor at Stanford University, explained why this distinction matters so much in practice. “Two patients with the same BMI may experience very different health effects,” he said. WHR gives doctors a clearer picture of the fat that actually drives disease.

The consequences of getting this wrong are real. When a patient’s BMI falls below a certain threshold, doctors may not recommend medication or surgery for weight loss. Insurance companies apply the same cutoffs to decide what they cover. People who receive the wrong classification simply do not get the help they need.

Mir Ali, MD, a bariatric surgeon in California, agreed that BMI has clear limits. He also explained why the medical community has not replaced it. “BMI remains the most widely used measure because it is easier to calculate,” he said. Tools like WHR and body composition scans deliver more accuracy, but they cost more and take longer to carry out.

The numbers at the population level tell a striking story. The CDC currently estimates that about 40% of American adults have obesity, using BMI as the measure. A separate report in JAMA from December 2025 put that figure closer to 75% when researchers factored in waist measurements. That difference accounts for tens of millions of people.

The CDC also reports that non-Hispanic Black adults carry higher obesity rates than other groups. Adults between 40 and 59 form the most affected age group. A flawed diagnostic tool hits these communities the hardest.

Obesity raises the risk of heart disease, type 2 diabetes, high blood pressure, and certain cancers. It also shortens life expectancy. Catching it early leads to more effective treatment and better outcomes.

Azagury summed it up directly. “Initiating effective therapy early is important, ideally before complications develop.” That process starts with knowing who actually needs help.

BMI is not going away anytime soon. It is simple, and doctors use it widely. But the evidence keeps building that it misses too many people. Until the medical community adopts something better as standard practice, a meaningful portion of Americans will go undiagnosed and untreated. Anyone with concerns about their own weight and health risks should speak with a healthcare provider about more complete screening options.