Fat and fat-free mass as important determinants of body composition assessment in relation to sarcopenic obesity.

Background: Fat and fat-free/muscle mass and their ratio reflecting the possible presence of obesity or sarcopenic obesity are important in assessing body composition.

Objective: The aim of the work was to assess the use of fat and fat-free mass and their ratio in the diagnosis of sarcopenic obesity, as well as correlations with selected anthropometric, somatic and biochemical parameters and indices.

Material and methods: The object of the study was a group of 201 women (20-68 aged) randomly selected from the population without the presence of a serious disease or without the use of medication. Body composition was assessed by the MFBIA method (InBody 720). We used the ratio of fat to fat-free mass (FM/FFM) to define sarcopenic obesity. A Biolis 24i Premium biochemical analyzer was used to determine biochemical parameters.

Results: Using FM and FFM values and their mutual ratio, we identified women with a healthy body weight (28.9%), obese women (58.2%) and women with sarcopenic obesity (12.9%). Values of anthropometric parameters (body weight, BMI, WC, WHR, WHtR, BAI, FM (kg, %), FMI, VFA, FFM (kg), FFMI, SMM (kg), SMMI, ICW, ECW, TBW, CHC, HC), with the exception of FFM (%), SMM (%) and TBW (%), increased significantly with increasing FM/FFM values, so the highest values were found in subjects with sarcopenic obesity. In the case of biochemical parameters, with increasing FM/FFM values, the values of T-CH, LDL, TAG, GLU, hs-CRP, UA, systolic and diastolic blood pressure also increased, so the highest values were again found in women with sarcopenic obesity. HDL values, on the contrary, decreased. FM/FFM had the strongest positive association with the proportion of fat mass on body weight (r=0.989), then with FMI (r=0.980), FM (r=0.965), VFA (r=0.938), WHtR (r=0.937), BMI (r=0.922), WC (r=0.901. We found the strongest negative association with the proportion of FFM on body weight (r=-0.989), the proportion of total body water (r=-0.988) and the proportion of skeletal muscle mass (r=-0.987).

Conclusions: FM/FFM correlates excellently with FM and VFA and can be implemented to diagnose obesity. In order to comprehensively evaluate the state of health and body composition, the proportionality of not only fat, but also fat-free/muscle mass should be analyzed, because it turns out that a negative impact on health and survival is associated not only with an excessive amount of adipose tissue, but also with a lower muscle mass.