What Does the ‘New’ Definition of Obesity Mean to You?

Many people think obesity is defined mainly by body weight or body mass index (BMI). But a new, widely endorsed definition suggests that where fat is carried—especially around the waist—may matter just as much as the number on the scale.

Under this proposed definition, about 75% of U.S. adults would meet criteria for obesity, compared with 40% based on BMI alone. While that number may be surprising, experts emphasize that the goal is not labeling—but better identifying health risks earlier and more accurately.

“Factors such as an expanded waistline really are associated with an increased risk for poor health outcomes,” says Kamil Faridi, MD, MSc, a Yale Medicine cardiologist. “We also know that obesity has a direct negative impact on nearly every organ system in the body, particularly the cardiovascular system.”

For decades, BMI—a calculation based on height and weight—has been the standard way to define obesity. A BMI of 30 or higher has previously been classified as obesity for most adults, while a BMI of 40 or higher alone is considered sufficient to diagnose obesity under the new framework. For Asian individuals, the recommended cutoff is lower.

But BMI has important limitations. It does not account for how much body fat a person has—or where that fat is located. As a result, it can miss people at increased health risk while mislabeling others who are metabolically healthy.

To address this, an international group of experts proposed a new definition in January 2025, published in The Lancet and endorsed by more than 75 medical organizations. The updated framework combines BMI with three other clinical measures, including:

• Waist circumference
• Waist-to-hip and waist-to-height ratios
• Evidence of weight-related conditions, such as high blood pressure, elevated blood sugar, or abnormal cholesterol levels

The report distinguishes between two categories—clinical obesity and preclinical obesity.

Clinical obesity: Excess body fat—often concentrated in the abdomen—that leads to organ dysfunction, functional impairment, or significant limitations in daily life. The definition includes specific clinical markers, such as diabetes, high blood pressure, or obstructive sleep apnea.

Preclinical obesity: Excess body fat that does not yet cause symptoms or physical impairment, but places a person at increased risk for developing obesity-related diseases in the future.

Dr. Faridi notes that having a clear definition matters because obesity thresholds influence insurance coverage, access to medications, and eligibility for treatments such as bariatric surgery or GLP-1 receptor agonists, including Wegovy and Zepbound.

Clinicians are not routinely using this new definition of obesity—yet. More research is needed before the definition becomes standard clinical practice, particularly to understand how it should be applied across age groups. For example, older adults tend to carry more weight around the middle than younger adults.

In the Yale-led study, obesity was common across all ages, but more than 90% of adults over 50 met criteria under the new definition, says Dr. Faridi, who was the lead author of the study.

“But the general framework is still very useful for clinicians who need to identify and manage patients they’re seeing in the clinic right now,” he adds. “It’s a total change in the way we think about obesity and really is an endorsement by the community to bring in these other measures so we can improve screening and identification.”

The health concern is abdominal (belly) fat, which causes the waistline to expand. A waist circumference greater than 34.6 inches for women and 40 inches for men is associated with increased risk for cardiometabolic disease.

This type of fat—called visceral adipose tissue—accumulates deep in the abdomen and surrounds organs such as the liver, pancreas, and kidneys. Unlike fat stored just under the skin, visceral fat is metabolically active and inflammatory.

“BMI doesn’t address any of that—it doesn’t address how much adipose tissue a person has, or importantly, where that fat is located,” Dr. Faridi says. “We know this extra fat tissue in the belly is not benign—it can contribute directly to disease.”

Obesity is linked to more than 200 conditions, including heart disease, diabetes, high blood pressure, fatty liver disease, sleep apnea, osteoarthritis, and certain cancers.

Waist circumference thresholds vary by population. For example, recommended cutoffs are lower for Asian adults—31.5 inches for women and 35.4 inches for men—because diabetes and related conditions tend to develop at lower body weights.

Yes, 75.2% of people in the U.S. are estimated to meet the criteria for obesity, according to the study, which was published at the end of December 2025 in Jama Network Open. By comparison, only 40% of Americans are considered obese based on BMI alone, says Dr. Faridi, who was the lead author.

The researchers based their findings on nationally representative data from over 14,000 people whose data was pulled from the National Health and Nutrition Examination Survey (NHANES), an ongoing national survey run by the CDC that measures the health and nutrition of adults and children in the U.S.

Many people classified as “normal weight” or “overweight” by BMI alone met criteria for obesity because of waist circumference measures.

“That’s how prevalence increased,” Dr. Faridi says. “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.”

The recommendations do not mean everyone needs medical treatment—but they do emphasize awareness. Dr. Faridi suggests knowing key health measures, including:

• Blood pressure
• Blood sugar
• Blood cholesterol
• Body weight and BMI
• Waist circumference

You can measure your waist at home by standing upright and placing a tape measure midway between your lowest rib and hip bone. Exhale normally before measuring.

Lifestyle changes remain foundational. Regular physical activity helps prevent weight gain, while calorie intake plays a larger role in weight loss. Small, sustainable changes—such as reducing sugar-sweetened beverages or increasing fiber-rich foods—can make a meaningful difference over time.

For some people, particularly those with significant weight-related health conditions, medications or other treatments may be appropriate, Dr. Faridi says, and should be discussed with a clinician.

Weight gain often occurs gradually, particularly during young and middle adulthood. “It’s really important for most young and middle-aged adults to make sure that they don’t gain excess abdominal fat over time,” Dr. Faridi says, noting that many people gain excess weight between ages 18 and 40 or 50.

For adults with borderline or elevated waist circumference, monitoring weight and waist size can be especially helpful during periods of stress, mental health challenges, or caregiving.

“If someone has excess body weight at any point, earlier intervention can prevent disease and improve long-term health,” he says.