University of Cambridge researchers propose new obesity definition, affecting 20 million Americans

A team of researchers from the University of Cambridge announced a new definition of obesity that could reclassify millions of adults as obese. The study, published on Monday in the journal Nature Medicine, proposes lowering the body‑mass index (BMI) threshold that marks obesity and adding waist‑circumference measurements to capture fat distribution. According to the authors, the change would shift about 20 million adults in the United States from the “overweight” to the “obese” category.

The move comes as public‑health officials grapple with a steady rise in obesity rates and criticism that BMI alone is an imperfect measure of health risk. BMI, which divides weight by height squared, does not account for muscle mass or where fat is stored. Recent evidence shows that abdominal fat is a stronger predictor of heart disease and diabetes than overall body weight. The study builds on earlier work by the World Health Organization, which has urged more nuanced metrics, but until now no consensus had been reached on how to implement them.

The proposed definition lowers the BMI cut‑off from 30 to 27 for adults, and couples it with a waist‑circumference threshold of 88 cm for women and 102 cm for men. The authors estimate that the new criteria would raise the obesity prevalence in the U.S. from 39 % to 52 %. Dr. Maria L. Hernandez, a co‑author, said the change would “unmask hidden risk” and help clinicians identify patients who need early intervention. The American Diabetes Association welcomed the proposal, noting that earlier detection could reduce costly complications. Critics warn that the shift could increase stigma and strain health‑care resources, but the authors argue that the benefits of earlier treatment outweigh these concerns.

The study’s authors are urging the World Health Organization to adopt the new criteria within the next two years. If the change is accepted, it could influence insurance coverage, public‑health guidelines, and research priorities. Health‑care providers may begin using the updated thresholds in routine screening, and insurers could adjust premiums and coverage for obesity‑related conditions. The broader impact will depend on how quickly policy makers and clinicians integrate the new definition into practice.