Recent research suggests that the body mass index (BMI) may be a more precise measure than previously believed. A study conducted by scientists at Johns Hopkins University and published in JAMA reveals that the majority of individuals classified as obese by BMI also possess significant excess body fat.
The study utilized a nationally representative sample from the National Health and Nutrition Examination Survey (NHANES), managed by the Centers for Disease Control and Prevention. It discovered that adults with an obese BMI also typically met obesity criteria based on waist circumference or body fat percentage. This supports the continued use of BMI as a tool for assessing obesity, even as its use is debated.
The researchers evaluated 2017-2018 NHANES data from participants who underwent additional tests alongside BMI assessments. Obesity is traditionally defined by a BMI of 30 and above, or 27 for individuals of Asian descent, but can also be determined by body fat percentage (25% for men, 35% for women) or waist circumference (40 inches for men, 35 inches for women).
The study found that over 98% of individuals considered obese by BMI alone also met obesity criteria when waist circumference or body fat percentage were included. The researchers noted that while specific populations, such as athletes, might need more thorough evaluation, they represent a small portion of the population.
This research is relevant amidst recent calls by experts for a shift in obesity diagnosis methods. These experts advocate for using multiple measurements of body size or direct body fat assessment rather than relying solely on BMI. They propose categorizing obesity into preclinical and clinical based on health impact.
While some advocate for phasing out BMI, the researchers highlight that direct body fat tests can be costly and resource-intensive. They suggest that many individuals might not benefit from such extensive testing.
The ongoing debate regarding BMI’s utility in diagnosing obesity continues, as highlighted by the findings. Presently, approximately 40% of U.S. adults are classified as obese under current BMI criteria, though recent trends and effective weight loss medication may be contributing to a decline.
