Age- and Sex-Specific Percentile Curves for the FM/FFM Ratio Using Data From the Canadian Longitudinal Study on Aging

Sarcopenic obesity is associated with a significant increase in morbidity and mortality, particularly in older adults. Common measures of sarcopenic obesity consider obesity and sarcopenia independently, despite their potentially synergistic harmful effects. The fat mass to fat-free mass ratio (FM/FFM) is an integrated measure of sarcopenic obesity that provides more useful information than measures that consider sarcopenia and obesity separately. The objectives of this study are to develop age- and sex-specific FM/FFM percentile curves for older adults and describe age- and sex-related patterns of FM/FFM percentiles.

Data from the Canadian Longitudinal Study on Aging (CLSA) were used (n = 28 791). FM/FFM was calculated as the ratio of total body fat mass (kg) to total body lean mass (kg) from dual-energy X-ray absorptiometry (DXA) scan. Weighted age- and sex-specific FM/FFM curves for the 1st, 5th, 25th, 50th, 75th, 95th and 99th percentiles were calculated using the LMS method. LMS provides a summary of the changing distribution of the measurement of interest by the three curves, lambda for the skewness (L), mu for the median (M) and sigma for the coefficient of variation (S). Weighted percentile curves were plotted with age (45-86 years) on the x-axis and FM/FFM on the y-axis for males and females, respectively.

Mean age of the CLSA at baseline was 59.6 ± 10.2 years, and 47.4% were males. For men, FM/FFM percentiles appear to increase slowly with aging and then stabilise after age 70. For women, FM/FFM percentiles appear to start at a higher value and increase more rapidly with aging, stabilising but then showing a stronger downward trend than males after age 65. At the 50th percentile, the maximum FM/FFM value is 0.42 at age 86 years for males and 0.71 at age 68 years for females.

The present study highlights the important age- and sex-related differences in FM/FFM percentiles in older adults. The FM/FFM curves could be used as a tool for identifying older adults with sarcopenic obesity and examining health risks associated with sarcopenic obesity.