Researchers Question BMI's Accuracy in Detecting Obesity-Related Diseases - Video

A healthy BMI may not tell the whole story when it comes to obesity.

A new study from Keck Medicine of USC, published in the Annals of Internal Medicine, suggests that millions of people who are considered a healthy weight by traditional standards may actually have obesity-related health risks that go undetected. The findings challenge the long-standing reliance on Body Mass Index (BMI), a measure based only on height and weight.

Researchers found that about one in four adults with a normal BMI met the criteria for what experts now call clinical obesity. Even more striking, half of those classified as overweight by BMI would be considered obese under the newer definition.

Unlike BMI, clinical obesity focuses on excess fat around the abdomen, known as adipose fat, which is strongly linked to inflammation and chronic disease. This deeper abdominal fat can damage organs and increase the risk of conditions such as heart disease, diabetes, high blood pressure, liver disease, and certain cancers.

The study analyzed data from nearly 5,600 adults who participated in the National Health and Nutrition Examination Survey. Researchers compared BMI classifications with a newer assessment method that uses waist circumference, waist-to-hip ratio, and waist-to-height ratio. Individuals who showed excess abdominal fat and obesity-related health problems were classified as clinically obese, regardless of their BMI.

BMI has important limitations because it cannot distinguish between fat, muscle, and bone. A muscular person may have a high BMI without excess fat, while someone with little muscle mass can have a normal BMI but still carry harmful levels of abdominal fat.

The findings suggest that relying solely on BMI could cause many at-risk individuals to miss out on early interventions, including lifestyle counseling, weight-management programs, medications, or other treatments that could improve long-term health outcomes.

The message is clear: a "normal" BMI does not always guarantee metabolic health, and obesity may be more common than previously recognized.

REFERENCE: Elhence, H., et al. (2026). National Prevalence of Clinical Obesity by BMI Class: A National Cross-Sectional Study. Annals of Internal Medicine. DOI: 10.7326/annals-25-05287. https://www.acpjournals.org/doi/10.7326/ANNALS-25-05287