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

A new study suggests that body mass index (BMI) may not be a sufficient indicator for metabolic health. Instead, researchers say a complete understanding of cardio-metabolic health also requires measurements of the body’s muscle, bone, and water percentage as well as the amount of fat in the abdominal versus the thighs.

The research was presented in June at ENDO 2023, the Endocrine Society’s annual meeting in Chicago, Illinois. At the meeting, Aayush Visaria, MD, MPH, an internal medicine resident at the Rutgers Robert Wood Johnson Medical School in New Brunswick, New Jersey, described how she and her colleagues conducted the investigation and what they found.

"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," said Visaria.

For the study, Visaria and her colleagues identified non-pregnant adults from the United States aged 20-59 years from the 2018 National Health and Nutrition Examination Survey with whole body dual x-ray absorptiometry (DEXA) scan data. The researchers categorized the subjects’ BMI by their ethnicity.

Then, investigators estimated the odds of obesity among adults as normal or overweight based on BMI or total body fat percentage as equal to or more than 25 percent in males and 32 percent in females by race. The researchers also estimated mean DEXA adiposity measures by race.

The study showed that nearly 36 percent of the subjects were considered obese by BMI standards, a BMI of 30 or more. However, according to obesity standards of total body fat percentage, 74 percent of the participants had obesity.

The data also suggested that Asian Americans and Hispanics with seemingly normal BMIs were more likely to have obesity according to total body fat standards as well as a greater proportion of abdominal fat than non-Hispanic whites. In addition, the research indicated that non-Hispanic blacks had significantly lower chances of obesity at normal to overweight BMI ranges and a lower proportion of abdominal fat.

According to Visaria, these results highlight the inconsistencies in determining obesity rates and metabolic health through BMI measurements alone.

"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 in a statement.