Obesity, a significant health concern, is often assessed using Body Mass Index (BMI). While some argue for alternative methods, a new study suggests BMI remains a robust indicator of excess body fat, particularly at the population level. This research, published in JAMA, challenges recent calls to phase out BMI as the primary obesity diagnostic tool.
Study Reinforces BMI’s Validity
Researchers at Johns Hopkins University analyzed data from the 2017-2018 National Health and Nutrition Examination Survey (NHANES). This survey, conducted by the Centers for Disease Control and Prevention (CDC), tracks Americans’ dietary and lifestyle habits. The study focused on participants who underwent both BMI assessments and additional measurements like body fat percentage and waist circumference. Traditional obesity criteria include a BMI of 30 or higher (27 for individuals of Asian descent). Alternative criteria involve body fat percentages (25% for men and 35% for women) or waist circumferences (40 inches for men and 35 inches for women).
The study found a strong correlation between BMI and other obesity measures. Over 98% of individuals classified as obese based on BMI also met the obesity criteria based on waist circumference or body fat percentage. This high concordance suggests that BMI effectively identifies individuals with substantial excess adiposity.
Implications for Obesity Diagnosis
This research comes at a pivotal time in obesity medicine. Earlier this year, experts advocated for a shift away from solely relying on BMI for obesity diagnosis. They proposed using two body size measurements (including BMI) or direct body fat measurements. They also suggested categorizing obesity as preclinical or clinical, based on the presence of obesity-related health issues.
Furthermore, body positivity and fat acceptance movements have long criticized BMI, advocating for its removal. These views have gained support from organizations like the American Heart Association and the World Obesity Federation.
Cost-Effectiveness and Accessibility of BMI
The Johns Hopkins researchers acknowledge the benefits of alternative measurements but highlight the practicalities. Direct body fat assessments require specialized equipment and may increase out-of-pocket costs for patients. Given the strong correlation between BMI and other measures, they suggest the added expense and effort may not be necessary for most individuals.
Ongoing Debate and Future Directions
The study concludes that for the vast majority of US adults with elevated BMIs, confirming excess adiposity with other methods might offer limited additional value. While the debate continues, BMI remains a relevant tool for assessing obesity, especially at the population level. Current estimates indicate approximately 40% of US adults are obese, although this figure may be declining due to the introduction of new weight-loss medications like Wegovy.
The researchers note further investigation may be warranted for specific populations like athletes. However, they emphasize that such cases represent a small percentage of the population. The debate surrounding BMI’s role in obesity diagnosis likely will continue. However, this study provides valuable evidence supporting its continued relevance as a reliable and accessible obesity indicator.
