Sarcopenic Obesity : Definition , Health Consequences and Clinical Management

Over the last decade, a new condition, which occurs in the presence of both sarcopenia and obesity, has been termed “sarcopenic obesity”. The term describes the coexistence of obesity, defined as the increase in body fat mass deposition, and sarcopenia, defined as the reduction in lean mass and muscle strength. However, many uncertainties still surround the condition of sarcopenic obesity in terms of its definition, the adverse shortand long-term health effects (i.e., medical disease, psychosocial functioning, quality of life and mortality) and its clinical management. The aim of this short communication is to emphasize some crucial aspects that future research should take into account in order to avoid bias and misinterpretations and to underline that the study of sarcopenic obesity should be considered a scientific and clinical priority, as reported by the European Society for Clinical Nutrition and Metabolism (ESPEN) and the European Association for the Study of Obesity (EASO).


INTRODUCTION
The term sarcopenia was initially used to refer to an age-related progressive loss of lean mass and muscle strength [1], known to be associated with morbidity, reduction in quality of life, frailty disability and increased rates of mortality.With the increasing prevalence of obesity worldwide [2], a new condition, which occurs in the presence of both sarcopenia and obesity, has been termed "sarcopenic obesity" [3].However, many uncertainties still surround this phenomenon with regard to the definition, the potential "negative effects" on health (i.e., medical diseases, psychosocial impairment) and the clinical implications and usefulness in terms of its treatment.
The aim of this short communication is to emphasize some crucial aspects that future research should take into account in order to avoid bias and misinterpretations and to underline that the study of this condition should be considered a scientific and clinical priority, as reported by the European Society for Clinical Nutrition and Metabolism (ESPEN) and the European Association for the Study of Obesity (EASO).In doing so, the following questions should be addressed: What is the definition of sarcopenic obesity?I.
Is sarcopenic obesity harmful to health?II.
Is this condition worth treating?III.

DEFINITION OF SARCOPENIC OBESITY
Over the last decade, the clinical definition and diagnostic criteria for sarcopenia have been developed and both are now widely accepted and recognized by the international scientific community [4].However, no consensus has yet been reached on how to define sarcopenic obesity.In most studies, the definition of sarcopenic obesity has relied on body composition phenotypes (i.e., lean mass) [4 -7], low muscle strength (i.e., weak handgrip strength) and poor physical performance (e.g., slow walking) [4,6,7] cut-offs, usually used for the definition of sarcopenia in elderly people [4].However, without accounting for body mass (i.e., body mass index, body surface), definitions of sarcopenia in obesity that are based only on lean mass and physical fitness may be strongly skewed for at least two reasons.Firstly, patients with obesity tend to have a relatively large lean mass.Hence, sarcopenia criteria based on this parameter may not be met in these individuals and the prevalence of sarcopenia may, therefore, be greatly underestimated [8].Secondly, low physical fitness is more strongly associated with obesity than with sarcopenia [9], with the result that the prevalence of sarcopenia may be overestimated.
To address this problem, recent reports have recommended accounting for body mass or body fat mass when identifying individuals with sarcopenic obesity [8].In light of this recommendation, a new definition of sarcopenic obesity has been established, which in addition to the Appendicular Lean Mass (ALM) also includes the Body Mass Index (BMI) [10].The following cut-offs have been proposed: ALM/BMI <0.804 in males and <0.582 in females [11].Despite this progress, a lot of work is still needed to reinforce the concept of a suitable definition of sarcopenic obesity in order to avoid false positives and negatives.This issue is of extreme importance as the correct identification of sarcopenic obesity is fundamental to target interventions only on those patients that are really affected by this condition [12] (Fig. 1).

Fig. (1)
. Suggested approach to the study the sarcopenic obesity.
Diagnostic criteria that accurately define sarcopenic obesity, accounting for body mass, body fat or body surface consensus regarding the definition and diagnostic criteria Longitudinal studies that assess the effect of sarcopenic obesity on the onset/evolution of diseases and mortalityEvidence-based consensus regarding the cause-effect