Impact of exercise training on the sarcopenia criteria in non-alcoholic fatty liver disease: a systematic review and meta-analysis

Exercise in the Management of Metabolic-Associated Fatty Liver Disease (MAFLD) in Adults: A Position Statement from Exercise and Sport Science Australia

Metabolic-associated fatty liver disease (MAFLD) is the most prevalent chronic liver disease worldwide, affecting 25% of people globally and up to 80% of people with obesity. MAFLD is characterised by fat accumulation in the liver (hepatic steatosis) with varying degrees of inflammation and fibrosis. MAFLD is strongly linked with cardiometabolic disease and lifestyle-related cancers, in addition to heightened liver-related morbidity and mortality. This position statement examines evidence for exercise in the management of MAFLD and describes the role of the exercise professional in the context of the multi-disciplinary care team. The purpose of these guidelines is to equip the exercise professional with a broad understanding of the pathophysiological underpinnings of MAFLD, how it is diagnosed and managed in clinical practice, and to provide evidence- and consensus-based recommendations for exercise therapy in MAFLD management. The majority of research evidence indicates that 150-240 min per week of at least moderate-intensity aerobic exercise can reduce hepatic steatosis by ~ 2-4% (absolute reduction), but as little as 135 min/week has been shown to be effective. While emerging evidence shows that high-intensity interval training (HIIT) approaches may provide comparable benefit on hepatic steatosis, there does not appear to be an intensity-dependent benefit, as long as the recommended exercise volume is achieved. This dose of exercise is likely to also reduce central adiposity, increase cardiorespiratory fitness and improve cardiometabolic health, irrespective of weight loss. Resistance training should be considered in addition to, and not instead of, aerobic exercise targets. The information in this statement is relevant and appropriate for people living with the condition historically termed non-alcoholic fatty liver disease (NAFLD), regardless of terminology.

The Roles of Non-Pharmacologic and Emerging Pharmacologic Management of Non-alcoholic Fatty Liver Disease and Sarcopenia: A Narrative Review

Non-alcoholic fatty liver disease (NAFLD) is one of the most prevalent causes of chronic liver disease worldwide which is often seen in patients with metabolic abnormalities such as those with obesity and insulin resistance. On the other hand, sarcopenia is a generalized and progressive skeletal muscle disorder characterized by low muscle strength, low muscle quality, low physical performance, or a combination of the three. Both disease entities share several underlying risk factors and pathophysiologic mechanisms. These include: (1) cardiometabolic overlaps such as insulin resistance, chronic systemic inflammation, decreased vitamin D levels, sex hormone modifications; (2) muscle-related factors such as those mitigated by myostatin signaling, and myokines (i.e., irisin); and (3) liver-dysfunction related factors such as those associated with growth hormone/insulin-like growth factor 1 Axis, hepatokines (i.e., selenoprotein P and leukocyte cell-derived chemotaxin-2), fibroblast growth factors 21 and 19 (FGF21 and FGF19), and hyperammonemia. This narrative review will examine the pathophysiologic overlaps that can explain the links between NAFLD and sarcopenia. Furthermore, this review will explore the emerging roles of nonpharmacologic (e.g., weight reduction, diet, alcohol, and smoking cessation, and physical activity) and pharmacologic management (e.g., roles of β-hydroxy-β-methylbutyrate, branched-chain amino acid supplements, and testosterone therapy) to improve care, intervention sustainability, and acceptability for patients with sarcopenia-associated NAFLD.

Change in skeletal muscle mass is associated with hepatic steatosis in nonalcoholic fatty liver disease

The association between nonalcoholic fatty liver disease (NAFLD) and sarcopenia is known. We aimed to determine the association between skeletal muscle mass changes and NAFLD status. This retrospective single-center study analyzed patients who underwent health screening twice between November 2009 and December 2017, with a temporal gap of 6 ± 0.5 years. The degree of sarcopenia was assessed using appendicular skeletal muscle mass (ASM) adjusted for weight and body mass index (BMI). Changes in hepatic steatosis and fibrosis status were evaluated using noninvasive serum markers. Patients with a decrease in ASM/BMI (n = 353) had increased hepatic steatosis index (HSI) and fatty liver index (FLI) scores during 6 years (p < 0.05). The baseline sarcopenia group had a greater elevation in NAFLD fibrosis score (NFS) over 6 years than those without baseline sarcopenia. ASM changes over 6 years showed a negative correlation with variations in HSI (β = - 0.96 in ASM/Weight and -28.93 in ASM/BMI) and FLI (β = - 5.44 in ASM/Weight and - 167.12 in ASM/BMI). Subgroup analyses showed similar results according to sex and age. Sarcopenia may worsen steatosis and vice versa. Skeletal muscle status can be used to predict the course of NAFLD and establish individualized treatment strategies.

Impact of Sarcopenia on the Severity of the Liver Damage in Patients With Non-alcoholic Fatty Liver Disease

An extensive body of the literature shows a strong interrelationship between the pathogenic pathways of non-alcoholic fatty liver disease (NAFLD) and sarcopenia through the muscle-liver-adipose tissue axis. NAFLD is one of the leading causes of chronic liver diseases (CLD) affecting more than one-quarter of the general population worldwide. The disease severity spectrum ranges from simple steatosis to non-alcoholic steatohepatitis (NASH), cirrhosis, and its complications: end-stage chronic liver disease and hepatocellular carcinoma. Sarcopenia, defined as a progressive loss of the skeletal muscle mass, reduces physical performances, is associated with metabolic dysfunction and, possibly, has a causative role in NAFLD pathogenesis. Muscle mass is a key determinant of the whole-body insulin-mediated glucose metabolism and impacts fatty liver oxidation and energy homeostasis. These mechanisms drive the accumulation of ectopic fat both in the liver (steatosis, fatty liver) and in the muscle (myosteatosis). Myosteatosis rather than the muscle mass per se, seems to be closely associated with the severity of the liver injury. Sarcopenic obesity is a recently described entity which associates both sarcopenia and obesity and may trigger worse clinical outcomes including hepatic fibrosis progression and musculoskeletal disabilities. Furthermore, the muscle-liver-adipose tissue axis has a pivotal role in changes of the body composition, resulting in a distinct clinical phenotype that enables the identification of the "sarcopenic NAFLD phenotype." This review aims to bring some light into the complex relationship between sarcopenia and NAFLD and critically discuss the key mechanisms linking NAFLD to sarcopenia, as well as some of the clinical consequences associated with the coexistence of these two entities: the impact of body composition phenotypes on muscle morphology, the concept of sarcopenic obesity, the relationship between sarcopenia and the severity of the liver damage and finally, the future directions and the existing gaps in the knowledge.

Impact of Sarcopenia and Myosteatosis in Non-Cirrhotic Stages of Liver Diseases: Similarities and Differences across Aetiologies and Possible Therapeutic Strategies

Sarcopenia is defined as a loss of muscle strength, mass and function and it is a predictor of mortality. Sarcopenia is not only a geriatric disease, but it is related to several chronic conditions, including liver diseases in both its early and advanced stages. Despite the increasing number of studies exploring the role of sarcopenia in the early stages of chronic liver disease (CLD), its prevalence and the relationship between these two clinical entities are still controversial. Myosteatosis is characterized by fat accumulation in the muscles and it is related to advanced liver disease, although its role in the early stages is still under researched. Therefore, in this narrative review, we firstly aimed to evaluate the prevalence and the pathogenetic mechanisms underlying sarcopenia and myosteatosis in the early stage of CLD across different aetiologies (mainly non-alcoholic fatty liver disease, alcohol-related liver disease and viral hepatitis). Secondly, due to the increasing prevalence of sarcopenia worldwide, we aimed to revise the current and the future therapeutic approaches for the management of sarcopenia in CLD.