Reply to the letter to the editor How is sarcopenic obesity positioned in the "obesity paradox"?

I read with great interest the article by Sabatino et al., recently published in Clinical Nutrition [[1]Sabatino A. Avesani C.M. Regolisti G. Adinolfi M. Benigno G. Delsante M. et al.Sarcopenic obesity and its relation with muscle quality and mortality in patients on chronic hemodialysis.Clin Nutr. 2023; 42 (PMID: 37418843. Online ahead of print): 1359-1368https://doi.org/10.1016/j.clnu.2023.06.032Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar]. They demonstrated that in hemodialyzed patients, those with sarcopenic obesity, defined as decreased abdominal skeletal muscle area and increased total abdominal fat area, had the highest all-cause mortality risk. They also suggested that myosteatosis, deterioration of muscle quality, increased the mortality risk in patients with sarcopenic obesity. It is indeed a fascinating article; however, some important issues need clarification. First, I recently proposed the potential clinical usefulness of simultaneous muscle and fat mass assessment using abdominal computed tomography (CT) to evaluate nutritional status and predict mortality [[2]Yajima T. Recommendation of simultaneously assessing abdominal fat and muscle-A clue to disclose a mystery of the “obesity paradox”.J Ren Nutr. 2023; (S1051-2276(23)00102-4) (PMID: 37315704. Online ahead of print)https://doi.org/10.1053/j.jrn.2023.05.009Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar]. Therefore, I fully agree with the methodology of Sabatino et al. While sarcopenic obesity is usually defined as a combination of sarcopenia, reduced muscle function and skeletal muscle mass, and obesity, increased body fat percentage [[3]Donini L.M. Busetto L. Bischoff S.C. Cederholm T. Ballesteros-Pomar M.D. Batsis J.A. et al.Definition and diagnostic criteria for sarcopenic obesity: ESPEN and EASO consensus statement.Clin Nutr. 2022; 41 ([Epub 2022 February 22]. PMID: 35227529): 990-1000https://doi.org/10.1016/j.clnu.2021.11.014Abstract Full Text Full Text PDF PubMed Scopus (74) Google Scholar], CT-assessed sarcopenic obesity has not yet been clearly defined. Therefore, its association with sarcopenic obesity should be examined. Second, Sabatino et al. categorized the patients into reference, obesity, sarcopenia, and sarcopenic obesity groups. However, it is unclear to which category patients with low skeletal muscle mass and abdominal fat mass, who are at a higher mortality risk than those with sarcopenic obesity [[4]Yajima T. Arao M. Yajima K. Takahashi H. Yasuda K. The associations of fat tissue and muscle mass indices with all-cause mortality in patients undergoing hemodialysis.PLoS One. 2019; 14 (PMID: 30759133)e0211988https://doi.org/10.1371/journal.pone.0211988.eCollection 2019Crossref Google Scholar], were assigned. Moreover, for the survival analysis, why were patients not categorized into groups with low or high abdominal skeletal muscle and total abdominal fat areas? Third, Sabatino et al. suggested that patients with sarcopenic obesity have poor muscle quality based on the increased intermuscular fat area and low attenuation muscle area. In the general population, myosteatosis is used as a surrogate marker for muscle quality [[5]Heymsfield S.B. Gonzalez M.C. Lu J. Jia G. Zheng J. Skeletal muscle mass and quality: Evolution of modern measurement concepts in the context of sarcopenia.Proc Nutr Soc. 2015; 74 (Epub 2015 Apr 8. PMID: 25851205): 355-366https://doi.org/10.1017/S0029665115000129Crossref PubMed Scopus (252) Google Scholar]. However, the associations between myosteatosis and muscle quality (handgrip strength and/or gait speed) have never been examined in patients on hemodialysis. Therefore Sabatino et al. should clarify these correlations before discussing the association between muscle quality and mortality risk in patients with sarcopenic obesity. Finally, based on the concept of the “obesity paradox,” an increase in fat and muscle mass can positively impact survival in hemodialysis patients by preventing protein-energy wasting. Thus, I believe that disclosing the positioning of sarcopenic obesity can help understand the “obesity paradox” in this population. Therefore, future studies on the associations between CT-measured abdominal muscle mass, muscle quality, visceral fat mass, subcutaneous fat mass, and mortality are required to understand the “obesity paradox” better. This research received no specific grant from public, commercial, or not-for-profit funding agencies.