BMI Alone Not a Complete Measure of Metabolic Health, Study Finds

Aayush Visaria

Credit: Rutgers Robert Wood Johnson Medical School

Body mass index (BMI) may not be a complete measure of metabolic health, as a high proportion of adults in the United States with normal BMI exhibit obesity, according to new research.¹

The findings, presented at ENDO 2023, highlighted the importance of including the percentages of the body that is fat, muscle, bone, and water, and how much fat is in the abdomen versus the thighs, to better understand drivers for cardiometabolic diseases.

“We show that there are racial/ethnic differences in body fat, BMI, and body fat distribution which may provide evidence for future studies to further determine if these differences are possible drivers of the racial disparities seen in cardio-metabolic diseases,” Aayush Visaria, MD, MPH, an internal medicine resident at the Rutgers Robert Wood Johnson Medical School, said in a statement.²

Previous findings have shown increasing trends in the prevalence of metabolically healthy obesity among adults in the US. According to a recent 20-year analysis, the age-standardized prevalence of metabolically healthy obesity increased from 3% in 1999-2002 to 7% in 2015-2018. The proportion of metabolically healthy obesity among adults with obesity also increased significantly from 11% to 15% over the same period, with disparities in trends across sociodemographic subgroups.

The current research identified non-pregnant adults in the United States aged 20 - 59 years from the 2011 - 2018 National Health and Nutrition Examination Survey (NHANES) with whole-body DEXA scan data. BMI was then categorized by ethnicity including non-Asian (underweight <18.5; normal, 18.5 - 24.9; overweight, 25 - 29.9; obese, ≥30 kg/m2) and Asian (underweight, <18.5; normal, 18.5 - 22.9; overweight, 23 - 27.4; obese, ≥27.5).

After categorization, the investigative team estimated the odds of obesity among adults as normal/overweight based on BMI or total body fat percentage as ≥25% in male and ≥32% in female patients, by race (non-Hispanic White, non-Hispanic Black, Asian, Hispanic, and other). In addition, the team estimated mean DEXA adiposity measures by race.

Upon analysis, the results showed that nearly 36% had BMI ≥30, the traditional definition of obesity, but 74% had obesity per total body fat percentage. Among adults with normal BMI, 44% of non-Hispanic White adults, 27% of non-Hispanic Black adults, 49% of Hispanic adults, and 49% of Asian adults had obesity as per total body fat percentage.

In addition, among adults with normal BMI, the mean android-to-gynoid fat ratio was 0.84 for non-Hispanic White adults, 0.85 for non-Hispanic Black adults, 0.89 for Hispanic adults, and 0.91 for Asian adults. Based on the total body fat percentage obtained from DEXA scans, nearly 3 in 4 young-to-middle-aged adults in the US were considered to have obesity.

The analysis showed Asian-American adults and Hispanic adults with seemingly normal BMI were more likely to have obesity, and more likely to have a greater proportion of abdominal fat than non-Hispanic White adults. Moreover, the data found that non-Hispanic Black adults had significantly lower chances of obesity at normal/overweight BMI ranges and a lower proportion of abdominal fat.

“We hope this research will add to the idea of weight-inclusive care and allow clinicians to 1) routinely use supplementary measures of body fat such as waist-circumference or bioimpedance-based body fat measurements (e.g. smart scales) in addition to BMI, 2) engage in practices to prevent unconscious biases that may occur when caring for a patient with obese BMI, and 3) engage in clinical decision-making that is not solely dependent on a BMI calculation but rather an overall idea of body composition and body fat distribution,” Visaria said.²

References

Wang J, Xia P, Ma M, et al. Trends in the Prevalence of Metabolically Healthy Obesity Among US Adults, 1999-2018. JAMA Netw Open. 2023;6(3):e232145. doi:10.1001/jamanetworkopen.2023.2145