The findings of a recent study suggest that, while BMI remains a dependable measure of adiposity, it is more accurate for women, younger individuals, and those of U.S. descent, with weaker correlations in older adults and the Korean/Asian population.
Body mass index (BMI) is an inexpensive and simple measure of obesity. However, BMI is not a perfect way to measure adiposity. BMI does not differentiate between lean mass and fat mass, which is one of its significant limitations. Nonetheless, it is quite a dependable measure, with a correlation to body fat mass as high as 0.72 to 0.86.
However, the accuracy of BMI in predicting body fat mass also depends on factors like age, sex, and race. A study published in Scientific Reports evaluated BMI compared to dual-energy X-ray absorptiometry (DXA)-derived measures, especially in the context of age, sex, and race.
BMI as a Body Fat Biomarker in People of Different Age, Sex, and Race
This was a retrospective study in which investigators used the National Health and Nutrition Examination Survey (NHANES) database from 1999 to 2006 for individuals older than 18 years and those who were assessed using DXA. The U.S. dataset included 18,061 participants (9141 men and 8920 women). To understand the racial differences, researchers utilized the Korea NHANES database from 2008 to 2011, including data for 8107 men and 10,754 women. The researchers then calculated the correlation between BMI and DXA-derived percentage body fat (PBF) and fat mass index (FMI).
BMI showed a strong association with FMI and PBF. This association was 0.944 for men and 0.976 for women. Hence, it is evident that BMI was a better predictor of body fat mass for women. Further, the study found that the correlation between BMI and DXA results weakened with age in both sexes. The study also found that BMI was less correlated to body fat content in the Korean population (truncal fat mass r = 0.836 in men and 0.884 in women). Among other biomarkers, insulin had a strong correlation with adiposity.
The Bottom Line
The study confirmed that BMI is a good indicator of adiposity overall. However, it was a better predictor for women than men. It was also more precise for young U.S. individuals than older people and less precise for those of Korean descent. The findings are in line with other, less extensive studies confirming the reliability of BMI. Like previous studies, it confirmed that BMI was less precise for older adults and Asians.
The study had some limitations; for example, NHANES U.S. and NHANES Korea may have different approaches to assessing body fat composition using DXA. Further, older adults are less likely to undergo DXA. Finally, Korean data is not an accurate representation of all Asians.
Source:
Jeong, S., Lee, D. H., Rezende, L. F. M., & Giovannucci, E. (2023). Different correlation of body mass index with body fatness and obesity-related biomarker according to age, sex and race-ethnicity. Scientific Reports, 13(1). https://doi.org/10.1038/s41598-023-30527-w
