Total and regional relationship between lean and fat mass with increasing adiposity-impact for the diagnosis of sarcopenic obesity

BACKGROUND/OBJECTIVE: Besides the effect of age used to define sarcopenia, there is need to understand the impact of adiposity on the relationship between lean (fat-free mass, FFM) and fat mass (FM) in order to diagnose sarcopenic obese phenotypes. More importantly, the regional distribution of skeletal muscle (SM) to adipose tissue (AT) or the composition of FFM (that is, SM proportion of lean mass) may also depend on adiposity. SUBJECTS/METHODS: In a large database (n=1737) of healthy males and females (age 11-84 years, BMI 13.5-52.5 kg/m(2)) we investigated changes in the relationship between FFM and FM (normalized by height as fat-free mass index and fat mass index: FFMI and FMI, kg/m(2) assessed by densitometry) with increasing adiposity and age. In a subgroup (n=263) we analyzed the relationship between regional SM and (i) AT (by magnetic resonance imaging) or (ii) lean soft tissue (by dual X-ray absorptiometry) with increasing adiposity. RESULTS: The relationship between lean and FM was influenced by adiposity, age and gender. With increasing adiposity, SM/AT declined faster at the trunk in men and at the extremities in women. The contribution of appendicular SM to lean soft tissue of arms and legs tended to decrease at a higher adiposity in both genders (FMI >6.97 kg/m(2) in women; FMI>7.77 kg/m(2) in men). CONCLUSION: Besides age and gender, adiposity and body region should be considered when evaluating the normal relationship between lean and FM, SM/FFM and SM/AT. European Journal of Clinical Nutrition (2012) 66, 1356-1361; doi:10.1038/ejcn.2012.138; published online 3 October 2012