Norm references of fat-free mass index and fat mass index and subtypes of obesity based on the combined FFMI-%BF indices in the Korean adults aged 18-89 yr

Abstract

Objective: To establish reference values for fat-free mass index (FFMI), fat mass index (FMI), and percent body fat (%BF) in a large Korean adult group of apparently healthy subjects, and to analyze the characteristics of body composition indices among the subtypes of obesity in Korean adults.

Subjects and methods: A multicenter, cross-sectional study was conducted on a sample of 1275 community-dwelling healthy Koreans, 504 men and 771 women, aged 18-89 years. Body composition parameters were measured by dual-energy X-ray absorptiometry. FFMI (FFM/height squared) and FMI (FM/height squared) were calculated, and then three subtypes of obesity were divided by FFMI; underlean (or sarcopenic), proportional, and heavy (or muscular) obesity.

Results: The reference values (5th-95th percentile) of the reference group (18-59 yr) for the FFMI was 16.3-22.3 kg/m(2) in men and 13.3-17.8 kg/m(2) in women. The %BF increased with age because of the reduction of FFM. Due to lower FFMI in the oldest men, they had the lowest BMI while FMI and BMI of Korean women increased with age like Caucasian women. The %BF among three subtypes of obesity was similar while FMI and BMI were increased as FFMI increased. The prevalence of underlean obesity in men was more than double in women.

Conclusion: It is essential to analyze FFMI as well as %BF because %BF alone cannot explain the effects of ageing on FFM and the characteristics of subtypes of obesity. This is the first study to present DXA-determined age- and sex-specific percentiles for body composition indices in Korean adults. These reference values may be useful for clinical evaluation of body composition and nutritional status for Korean adults.