Short communicationInverse relationship between “a body shape index” (ABSI) and fat-free mass in women and men: Insights into mechanisms of sarcopenic obesity
Introduction
Obese adults have, on the average, a larger skeletal muscle mass than normal weight or lean subjects, of the same age and sex. These differences are the result of the muscle anabolism induced by the loading effect of the heavier body weight associated with obesity [1]. There is a direct correlation between the body mass index (BMI) and muscle mass. Furthermore obese subjects, compared with non-obese, have a mean larger total daily energy expenditure from a higher resting metabolic rate, correlated with their increased skeletal muscle mass [2]. Despite these findings, obesity may be associated with sarcopenia, especially in the elderly or in patients with chronic diseases or cancer [3], [4]. Sarcopenic obesity is a syndrome characterized by a progressive and generalized loss of skeletal muscle mass and function, leading to adverse outcomes such as physical disability, poor quality of life and higher morbidity and mortality [3]. In the clinical setting, sarcopenic obesity is defined by a higher fat mass (FM) relative to fat-free mass (FFM). FM and FFM are clinically determined by bioelectrical impedance analysis (BIA) [3], [5], [6]. Mechanisms of obesity-related sarcopenia include activation of inflammatory mediators, oxidative stress, unbalanced hormonal milieu or unloading. Visceral adiposity may play a pivotal role in the development of sarcopenic obesity. Catabolic adipokines (IL-6, TNF-α, leptin, resistin, etc.) are preferentially released by visceral adipose tissue and may induce protein catabolism in skeletal muscle [7]. In addition, muscle unloading and physical inactivity directly promote visceral fat accumulation [8] causing systemic inflammation, oxidative stress and muscle atrophy [9], [10]. Despite the fact that mechanisms of sarcopenia are strictly linked to those of visceral adiposity, an inverse relationships between abdominal fat accumulation and lean body mass depletion have never been shown in clinical studies using the waist circumference (WC) as an index of abdominal fat. In fact, WC is positively correlated with BMI to the extent that it is difficult to differentiate the two as determinants of skeletal muscle mass.
To avoid the drawbacks regarding the direct relationship between BMI and WC, a body shape index (ABSI) has been recently developed as a new anthropometric parameter based on WC and BMI [11]. In large series of pooled male and female individuals, ABSI did not correlate with height, weight or BMI and strongly predicted morbidity and mortality [11], [12], [13]. In this study we have assessed the efficiency of ABSI to predict variability of the fat-free mass index (FFMI) (a height-normalized marker of lean body mass) in males and females with BMI >25 kg/m2.
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Subjects and methods
Two hundred consecutive overweight/obese patients (111 women and 89 men), excluding individuals with diabetes mellitus or other clinically relevant comorbidities (i.e. organ insufficiency, infection diseases, cancer), were recruited from the hospital outpatient obesity clinics of: Trieste (Italy), Bolzano (Italy) and Izola (Slovenia). The study was approved by the appointed ethics committees of Italy and Slovenia. All subjects provided written informed consent. For each patient, demographic,
Results
Characteristics of patients are shown in Table 1. Female and male subjects were comparable for age and BMI. FFMI was greater in men while the FM/FFM ratio was higher in women. The male subjects had greater WC and ABSI. Plasma insulin levels were more elevated in men while plasma CRP concentrations were not significantly different between genders. Pearson's correlations between different variables are shown in Table 2. WC was positively associated with BMI, while ABSI was not significantly
Discussion
We have investigated the relationship between abdominal fat deposition and skeletal muscle mass in overweight/obese women and men using, as surrogate markers, ABSI and FFMI. The ABSI is a recently introduced measurement of abdominal fat that may give a better measure of the central deposition of fat tissue [11], [12], [13]. The WC has been questioned as valid methods to assess the risk of visceral adipose tissue accumulation. WCs are highly and positively correlated (Table 2) to all parameters
Conflict of interest
None to declare.
Acknowledgments
Statement of authorship: GB, study concept and design, study supervision, data collection, manuscript draft. FGDG, data analyses, manuscript draft. AB, data collection, data analyses, manuscript draft. MC, data collection, data analyses. VB, data collection, data analyses. PV, data analyses, manuscript draft. GT, data analyses, critical revision of the manuscript for important intellectual content. LL, study design, study concept and design, data analyses, manuscript draft, critical revision of
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