New research reveals a revised definition of obesity, indicating that over 75% of U.S. adults could now be classified as obese. This stark increase is based on a recent study’s findings.

Currently, approximately 43% of Americans meet the traditional body mass index (BMI) standard of 30 or above. However, when researchers expanded the definition to include waist-to-height and waist-to-hip ratios, the estimated obesity prevalence soared to 75.2%.

A detailed analysis conducted by a research team from Yale School of Medicine and Harvard University emphasizes that relying solely on BMI may significantly underestimate the actual number of individuals with excess body fat.

According to the study director, Dr. Nora Al Roub, a professor at the Yale School of Public Health, “BMI is a straightforward calculation based on weight and height. While it is simple to compute, it does not provide insight into fat distribution or the composition of a person’s weight pertaining to fat versus muscle.” – BBC Science Focus.

The updated criteria classify all adults with a BMI of 30 or higher as obese, as well as 38.5% of individuals with a BMI under 25, which is typically deemed healthy.

Dr. Al Roub states, “This increase underscores how many individuals possess unhealthy levels of body fat, even while having a normal or slightly elevated BMI.”

The study notes that while these newly identified obese individuals may not require immediate medical interventions, they are at an elevated risk for conditions such as diabetes and heart disease, highlighting the importance of early preventive strategies.

The new guidelines, first suggested in January 2025 by the Lancet Diabetes and Endocrinology Committee led by Professor Francesco Rubino of King’s College London, have received endorsement from over 70 healthcare organizations.

Professor Rubino pointed out that the recent analysis may slightly misinterpret these guidelines. The additional metrics were intended to help identify individuals who may have obesity even if their BMI is just under the obesity threshold.

He further notes that the thresholds can differ based on gender and ethnicity, but generally, a BMI of 25 is considered well below the obesity classification.

Dr. Al Roub emphasized that the goal of the study was not to redefine obesity but to understand how population-level obesity estimates change when these criteria are uniformly applied to real-world datasets.

What are the Updated Guidelines for Obesity?

The new guidelines propose utilizing BMI as an initial screening tool to identify individuals at risk, followed by several additional measurements. While specific thresholds can vary by age, gender, and ethnicity, commonly accepted cutoffs include:

• Waist circumference of 102cm or more for men, and 88cm or more for women
• Waist-to-hip ratio of 0.9 or greater for men, and 0.85 or greater for women
• Waist-to-height ratio exceeding 0.5

To be categorized as obese, individuals must meet one of the following criteria:

• BMI of 40 or more
• BMI between 30-39 (or ethnicity-specific threshold) along with at least one additional measurement
• BMI less than but close to 30 (or ethnicity-specific threshold) plus at least two additional measurements

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