Physician-authored summaries and commentary on the most important medical research, provided by the NEJM Group, a division of the Massachusetts Medical Society.
© Massachusetts Medical SocietyJune 2025
Nearly all adults with body mass indexes that indicated obesity had excess fat mass.
Body mass index (BMI) does not distinguish between fat mass and muscle or bone mass, leading some to question its use as a measure of obesity. Excess adiposity is considered a more accurate measure, but it is less convenient because it involves waist circumference measurements or dual-energy x-ray absorptiometry (DEXA) scans. Investigators used 2017 to 2018 health survey data to assess the concordance of BMI and excess adiposity in 2225 adults (mean age, 39 years) who had undergone anthropometric and DEXA measurements. Obesity as measured by BMI was defined as 30 kg/m2 or above (or 27.5 kg/m2 or above in non-Hispanic Asian participants). Standardised criteria were used for excess adiposity as determined by waist circumference (e.g. 102 cm or greater for men other than non-Hispanic Asians) and DEXA scanning (e.g. 35% or higher body fat in women).
The rate of obesity was 39.7% based on BMI and 39.1% based on excess adiposity. Among participants with obesity based on BMI, 98% also had excess adiposity; in other words, essentially the same individuals were considered as obese by both criteria. Results were similar across all age, racial, ethnic and sex groups.
Comment: These results run counter to the concern that BMI might label patients inappropriately with obesity because of their nonfat mass. Although some special populations, such as athletes, might deserve special assessments, the effort and possible expense of measuring waist circumference or performing a DEXA scan appears to be unnecessary in routine practice.
Thomas L. Schwenk, MD, Dean Emeritus, University of Nevada, Reno School of Medicine, Reno; Professor Emeritus, University of Michigan Medical School, Ann Arbor, USA.
Aryee EK, et al. Prevalence of obesity with and without confirmation of excess adiposity among US adults. JAMA 2025 Apr 17; e-pub (https://doi.org/10.1001/jama.2025.2704).
This summary is taken from the following Journal Watch titles: General Medicine, Ambulatory Medicine.