A new definition of obesity has emerged, shifting the focus from body weight and body mass index (BMI) to the location of body fat, particularly around the waist. According to a study published in The Lancet and endorsed by over 75 medical organizations, this revised framework suggests that approximately 75% of U.S. adults would be classified as obese, compared to only 40% under the traditional BMI criteria.
Experts emphasize that the intent of this change is not merely to label individuals but to identify health risks more accurately. “Factors such as an expanded waistline really are associated with an increased risk for poor health outcomes,” stated Kamil Faridi, MD, MSc, a cardiologist at Yale Medicine. He highlighted that obesity can negatively impact nearly every organ system in the body, particularly the cardiovascular system.
Understanding the New Framework
Historically, obesity has been defined by BMI, which is calculated using height and weight. A BMI of 30 or higher has been classified as obesity for most adults, while a BMI of 40 or higher is now considered sufficient for diagnosis under the new criteria. For certain populations, such as Asian individuals, the recommended cutoffs are lower.
The new definition, proposed in January 2025, combines BMI with three additional clinical measures: waist circumference, waist-to-hip and waist-to-height ratios, and evidence of weight-related conditions, such as high blood pressure or elevated blood sugar. This approach distinguishes between two categories of obesity: clinical and preclinical.
Clinical obesity refers to excess body fat that results in organ dysfunction or significant limitations in daily life, including specific conditions like diabetes and obstructive sleep apnea. In contrast, preclinical obesity indicates excess fat that does not yet cause symptoms but increases the risk of future obesity-related diseases.
Dr. Faridi noted the importance of having a clear definition, as obesity thresholds can influence insurance coverage, access to medications, and eligibility for treatments. Although clinicians have not yet widely adopted this new framework, further research is necessary to establish its application across various age groups.
The Impact of Waist Circumference
Abdominal fat is a significant health concern, and a waist circumference exceeding 34.6 inches for women and 40 inches for men is associated with an increased risk of cardiometabolic diseases. This type of fat, known as visceral adipose tissue, accumulates around vital organs and is metabolically active, contributing to inflammation and various health conditions.
Dr. Faridi pointed out that BMI does not account for fat distribution or the amount of adipose tissue present. “We know this extra fat tissue in the belly is not benign—it can contribute directly to disease,” he explained. Obesity is linked to over 200 health conditions, including heart disease, diabetes, and certain cancers.
The study, published in December 2025 in JAMA Network Open, analyzed data from more than 14,000 participants in the National Health and Nutrition Examination Survey (NHANES). Findings revealed that many individuals classified as “normal weight” or “overweight” based on BMI alone met obesity criteria when waist circumference was considered.
Dr. Faridi remarked, “People can still be at increased risk for adverse health outcomes from excess adipose tissue—even if their BMI is not in the obese range.” This underscores the importance of awareness regarding health measures, including blood pressure, blood sugar, and waist circumference.
While not everyone classified under the new criteria requires medical treatment, the focus is on raising awareness. Dr. Faridi advises that individuals monitor key health measures and consider lifestyle changes. Regular physical activity and managing calorie intake play crucial roles in weight management. Sustainable changes, such as reducing sugar-sweetened beverages or increasing fiber-rich foods, can lead to significant improvements over time.
For those with significant weight-related health conditions, medications or treatments may be necessary, and discussions with healthcare providers are essential. Dr. Faridi emphasized that preventing excessive abdominal fat gain is vital, particularly for young and middle-aged adults, as weight gain often occurs gradually during these life stages.
Monitoring weight and waist size can be particularly beneficial during periods of stress or mental health challenges. “If someone has excess body weight at any point, earlier intervention can prevent disease and improve long-term health,” Dr. Faridi concluded.
As awareness around this revised definition of obesity grows, the medical community aims to enhance the identification and management of obesity-related health risks, ultimately improving patient outcomes.
