The impact of DXA-derived fat-free adipose tissue on the prevalence of low muscle mass in older adults.

BACKGROUND/OBJECTIVES: To investigate the impact of eliminating fat-free adipose tissue (aFFAT) on the prevalence of low muscle mass in older adults.

SUBJECTS/METHODS: Three hundred and forty-three (153 men and 190 women) well-functioning Japanese older adults (aged 65-79) had their appendicular lean mass (aLM) and appendicular fat mass (aFM) measured using dual-energy X-ray absorptiometry (DXA). aFFAT was then estimated from DXA-derived aFM (aFM = (FM/0.15)*0.85). Both traditional cutoffs and those corrected for aFFAT were used for diagnosing low muscle mass.

RESULTS: With traditional cutoff values, the prevalence of low muscle mass using the unadjusted aLM index was 20.1%. After adjusting the aLM index for aFFAT, the prevalence increased to 49.0% (p < 0.001). However, when the cutoff values were also adjusted for aFFAT, the prevalence of low muscle mass only increased to 23.0% (p < 0.001). Further, ~5% of the participants (7 men and 8 women) were newly classified as having low muscle mass after correction for aFFAT. However, several women (n = 5) were not classified as having low muscle mass using the corrected cutoff value, although they would have been when using the non-corrected cutoff.

CONCLUSIONS: Adjusting for the effect of aFFAT on DXA-derived aLM significantly increases the prevalence of low muscle mass in older adults. For clinical research and practice, the influence of aFFAT on DXA-derived aLM may need to be taken into consideration when diagnosing low muscle mass.