Body Fat Or Lean Mass - Which Is More Important For An Aging Population?

It is well accepted that body fat increases and muscle mass decreases as a part of the normal aging process. While increased levels of body fat are a concern for health-related diseases (e.g., diabetes, coronary artery disease), losses in lean mass have implications for an individual’s ability to function independently. Both subsequently impact morbidity and mortality. PURPOSE: To examine the relationship between body fat (% fat) and lean tissue in adults aged 50 and older. METHODS: Participants were 63 females (57.4 ± 7.3 yr) and 38 males (60.5 ± 7.7 yr) who reported to the laboratory after refraining from food, water, and exercise for at least 2 hours. During a single visit, % fat and appendicular lean mass (ALM) were assessed via bioelectrical impedance analysis (BIA). Body mass index (BMI) was calculated from measured height (stadiometer) and weight (via BIA). Based on three published operational definitions for sarcopenia, lean mass is reported as 1) ALM alone, 2) ALM adjusted for stature (ht in m2; ALM/Ht), and 3) ALM adjusted for BMI (ALM/BMI). RESULTS: Our results showed a significant relationship between BMI and % fat (r = 0.647, p < 0.001) as well as between % fat and ALM/BMI (r = -0.627, p < 0.001). Of the 101 participants, 54 (29F, 25 M) were categorized as overweight according to BMI (≥25 kg/m2) and 38 (22F, 16 M) were overfat when utilizing % fat (sex specific cut-points according to Gallagher et al., 2000; i.e., >36.5%F, >24%M). In terms of lean mass, 15 participants were characterized as having low lean mass by at least one method (ALM/BMI: n = 11, 4F, 7 M; ALM/Ht: n = 8, 2F, 6 M; ALM alone: n = 8, 4F, 4 M). Of these 15 participants, 11 were characterized as overweight by BMI and 8 as overfat according to % fat. In our population, a much higher proportion of individuals were categorized as “at risk” according to BMI (53.5%) and/or % fat (37.6%) than low lean mass (sarcopenia: 14.9%). CONCLUSION: Our results suggest that the ALM/BMI method suggested by Dam et al. (2014) was more likely to identify those with low lean mass, thus may be utilized as a screening tool for sarcopenia. In conjunction with this value, % fat can be used to identify those who are sarcopenically obese – a population that is at risk for both long-term health and short-term functional issues.