National Reference Values of FFMI and FMI Using Body Composition Chart in Korean Adults

Area of Science:

• Human Physiology
• Body Composition Analysis
• Public Health

Background:

• Body mass index (BMI) fails to differentiate between fat mass (FM) and fat-free mass (FFM).
• Fat-free mass index (FFMI) and fat mass index (FMI) offer a more detailed assessment of body composition by normalizing FFM and FM to height squared.
• Establishing national reference values is crucial for accurate body composition assessment in diverse populations.

Purpose of the Study:

• To establish the first nationally representative, Bioelectrical Impedance Analysis (BIA)-based FFMI and FMI reference values for Korean adults.
• To visualize body composition trajectories across different age groups.
• To classify obesity subtypes using a novel body composition chart.

Main Methods:

• Analysis of cross-sectional data from 10,140 Korean adults (aged 10-80 years) from the KNHANES IX (2022-2023) survey.
• Measurement of FFM and FM using multifrequency BIA (InBody 970).
• Classification of obesity subtypes (underlean, proportional, heavy) based on FFMI and FMI percentiles relative to an 18-59-year-old reference group.

Main Results:

• In men, FFMI peaked in middle age and declined significantly by 70-80 years, while FMI remained stable.
• In women, FMI showed a substantial increase with age, accompanied by stable FFMI.
• Prevalence of underlean obesity in men increased markedly with age (0.7% in 30-39 years to 17.4% in 70-80 years), often missed by traditional BMI or waist circumference measurements.

Conclusions:

• The developed FFMI and FMI reference values provide essential benchmarks for assessing body composition in Korean adults.
• The body composition chart serves as a practical tool for identifying underlean obesity, a condition not adequately captured by BMI.
• These findings underscore the importance of utilizing detailed body composition metrics beyond BMI for comprehensive health assessments.