Fatty liver index and somatic composition in subjects receiving medical health checkup.

Aims: To elucidate the relationship between fatty liver index (FLI) and somatic composition among health checkup recipients (4533 men and 4877 women).

Methods: Fat (F) index, fat-free (FF) index, and fat mass to fat-free mass (F-FF) ratio was measured by bioimpedance analysis. Skeletal muscle mass (SMM) loss was defined as FF index <18 kg/m² in men and FF index <15 kg/m² in women. The impact of FLI on the somatic composition (i.e., F index, FF index, and F-FF ratio) was retrospectively investigated.

Results: The median age in men and women was 54 and 52 years (p < 0.0001). The median body mass index in men and women was 23.4 and 21.1 kg/m² (p < 0.0001). The prevalence of fatty liver on ultrasonography was 52.5% in men and 22.1% in women. The median FLI in men and women was 25.1 and 6.9 (p < 0.0001). Fatty liver index correlated significantly with F index (r > 0.5 in all analyses). In all analyses, the decreased SMM group had significantly lower FLI than the nondecreased SMM group. In receiver operating characteristic (ROC) curve analysis for the SMM decrease, in both genders, area under the ROCs of FLI were all over 0.80 (optimal cut-off point: 19.7 in men and 8.4 in women). The FLI correlated significantly with F-FF ratio (r > 0.5 in all analyses).

Conclusion: The FLI can be a good indicator of not only fat mass but also FF mass and body composition balance in health checkup subjects. The FLI may not be just a marker of hepatic steatosis.