Fat-free mass index cutoff values for reduced muscle mass in older community-dwelling adults in Japan: A descriptive cohort study

Background

The Global Leadership Initiative on Malnutrition criteria emphasize the importance of assessing muscle mass, recommending the fat-free mass index (FFMI) as a key measure. This study aimed to establish FFMI cutoff values for Japanese individuals and examine the risk factors of falls using these values.

Methods

This descriptive cohort study included 696 older adults from a Japanese outpatient frailty clinic located within a hospital. FFMI was measured via bioelectrical impedance analysis, and the appendicular skeletal muscle index (ASMI) was measured using dual-energy X-ray absorptiometry. Receiver operating characteristic analysis identified optimal FFMI cut-offs against low ASMI (<7.0 kg/m² for men; <5.4 kg/m² for women). Logistic regression was used to analyze the relationship between reduced muscle mass and falls over 1 year.

Results

Participants (mean age 76.1 ± 7.4 years; 64.8% female) experienced falls in 180 cases (25.9%), with 244 participants (35.1%) exhibiting low ASMI. The optimal FFMI cut-offs were <17.5 kg/m² for men (area under the curve [AUC]: 0.926; 95% confidence interval [CI]: 0.893–0.958) and <14.4 kg/m² for women (AUC: 0.927; 95% CI: 0.902–0.953), yielding 84.0% sensitivity, 91.2% specificity, and 88.6% accuracy. Low ASMI was not significantly linked to falls (odds ratio [OR: 1.04; 95% CI: 0.70–1.53; P = 0.860), whereas low FFMI was predictive (OR: 1.49; 95% CI: 1.01–2.20; P = 0.044).

Conclusion

FFMI cut-offs of <17.5 kg/m² for men and <14.4 kg/m² for women effectively identified reduced muscle mass and predicted falls. The results suggest that FFMI may be a useful tool in malnutrition diagnosis.