Measuring the waist may be one of the simplest ways to reveal hidden health risks linked to excess body fat, according to a new analysis by Rutgers Health researchers. The study, published in JAMA Network Open, suggests that clinicians may not need a complicated series of body measurements to identify adults whose fat distribution places them at elevated risk of diabetes, cardiovascular disease, stroke and certain cancers. Instead, a tape measure used alongside body mass index, or even by itself, performed nearly as well as a recently proposed definition of obesity that combines several indicators of body composition. The findings challenge the idea that more measurements automatically produce a more accurate diagnosis and point toward a practical screening tool that could be used in almost any primary care setting.
The researchers analyzed data from 1,900 adults between the ages of 20 and 59 who took part in the U.S. National Health and Nutrition Examination Survey, a long-running program that combines interviews, physical examinations and laboratory testing to track the health of the population. Participants’ body fat was assessed using a highly accurate reference method, allowing the investigators to compare several clinical definitions of obesity against a more direct estimate of adiposity. Adiposity refers to the amount of body fat a person carries, while obesity is a medical condition in which excess body fat is associated with impaired health or an increased likelihood of disease. The distinction matters because body weight alone cannot reliably reveal how much of that weight is fat, muscle, bone or fluid.
The analysis focused in part on a recently proposed framework developed by an international, multidisciplinary group of experts and commonly described as the Lancet definition of obesity. Rather than relying only on BMI, the framework incorporates waist circumference, waist-to-height ratio and waist-to-hip ratio. BMI is calculated by dividing weight in kilograms by height in meters squared, but it is an indirect measure and cannot distinguish muscle from fat. Nor does it show where fat is stored. Two people with the same BMI can have very different levels of visceral fat, the metabolically active fat accumulated around internal organs. Visceral fat is strongly associated with insulin resistance, abnormal blood lipids, inflammation and high blood pressure, making the location of fat clinically important.
The Rutgers team found that a simpler definition based on either BMI or waist circumference provided a better balance between sensitivity and specificity than the more complex framework. Sensitivity describes how well a test identifies people who truly meet a body-fat criterion for obesity, while specificity measures how effectively it avoids labeling people as having obesity when they do not. A test with high sensitivity but poor specificity may produce many false-positive results, potentially leading to unnecessary concern or follow-up testing. Conversely, a highly specific test can miss people who face genuine health risks. In this study, using BMI or waist circumference captured relevant cases while limiting the number of inaccurate classifications.
Waist circumference alone also performed nearly as well as the combined approach. That result is important because abdominal fat can be a stronger marker of metabolic risk than total body weight. Fat stored beneath the skin is not biologically identical to fat surrounding the liver, pancreas and intestines. Visceral adipose tissue can release fatty acids and signaling molecules that interfere with insulin action and promote chronic, low-grade inflammation. Over time, these processes can contribute to elevated blood glucose, type 2 diabetes, fatty liver disease and atherosclerosis. A waist measurement cannot directly quantify visceral fat, but it provides an accessible proxy for central fat accumulation and can identify risk that BMI may overlook.
The researchers emphasized that BMI alone missed a substantial proportion of adults who met the study’s body-fat criteria for obesity. This limitation has been recognized for decades, particularly among people with high muscle mass, older adults who have lost muscle, and individuals whose fat is concentrated around the abdomen. BMI may also perform differently across sex, age and ancestry groups because the relationship between body mass, body fat and disease is not identical in every population. A person can fall below a conventional BMI threshold while carrying a level of abdominal fat associated with metabolic disease. Conversely, a muscular person may have a high BMI without having an unhealthy amount of body fat. Adding waist circumference can provide information that the scale and height-based calculation cannot.
The investigators noted that the measurements required by the newer framework may be difficult to incorporate into ordinary medical visits. Hip circumference, in particular, is rarely recorded in routine clinical practice, and calculating several ratios introduces additional opportunities for measurement or calculation errors. Waist circumference, by comparison, can be obtained quickly with a flexible tape measure. For consistency, clinicians generally measure around the abdomen at a defined anatomical location, with the person standing naturally and breathing normally. The exact protocol matters because measurements can vary depending on where the tape is placed, how tightly it is pulled and whether the abdomen is held in or expanded. Even with those limitations, the procedure requires little equipment and can be repeated over time to monitor change.
“Pay attention to the need to loosen your belt or get bigger pants,” said Aayush Visaria, a Rutgers Health researcher and the study’s lead author. Clothing size is not a standardized medical measurement, but a gradual increase in waist size may serve as an early warning that body fat is accumulating. Visaria said that measuring the waist together with body weight could help identify health risks earlier, creating an opportunity for people and clinicians to address diet, physical activity, sleep, medications and other factors before disease develops. The researchers are not suggesting that waist circumference replace clinical judgment or laboratory testing. Rather, they argue that it should be used as a practical screening signal that can prompt a fuller evaluation of blood pressure, glucose, cholesterol and overall health.
The findings may influence future recommendations for obesity screening, particularly as medical organizations reconsider whether BMI should remain the dominant entry point for diagnosis. The study does not establish a universal waist threshold for every individual, nor does it prove that a single measurement can predict a person’s future health with certainty. It is based on observational survey data and uses body-fat criteria as the reference standard, while the biological effects of obesity also depend on age, genetics, fitness, existing disease and the duration of excess fat exposure. Still, the results offer a strikingly simple message: a tape measure may capture much of the clinically useful information provided by a far more elaborate assessment. In a health system where time and resources are limited, that simplicity could make waist measurement one of the most widely useful tools for detecting obesity-related risk.
Subject of Research: People
Article Title: Lancet Definition vs Other Criteria for Obesity Diagnosis in Adults
News Publication Date: 7-Aug-2026
Web References: Rutgers Health study announcement: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2852541?widget=personalizedcontent&previousarticle=2852509; DOI: https://doi.org/10.1001/jamanetworkopen.2026.27738
References: JAMA Network Open, “Lancet Definition vs Other Criteria for Obesity Diagnosis in Adults,” DOI: 10.1001/jamanetworkopen.2026.27738
Keywords: Body mass index, waist circumference, obesity, body fat, metabolic disorders, nutrition disorders, weight loss, diabetes, cardiovascular disease, visceral fat
