This project aims to evaluate the roles of the autonomic nervous system (ANS) and gut microbiota as correlates of clinical improvement in metabolic dysfunction-associated fatty liver disease (MAFLD) and non-alcoholic fatty liver disease (NAFLD) in response to a therapeutic regimen comprising resistance exercise and probiotic supplementation. The primary objective is to investigate the effects of these non-pharmacological interventions on MAFLD/NAFLD and to identify patient phenotypes based on baseline ANS profiles and gut microbiota composition that predict clinical responses.

The human microbiome, understood here as the collective community of microorganisms, their genetic material, and metabolic products that colonize the body from birth, is particularly concentrated in the gut. The gut microbiome, dominated primarily by anaerobic bacteria, encompasses thousands of species and millions of genes distributed among the major phyla: Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, and Verrucomicrobia. Recent research has increasingly focused on the gut microbiome due to its dysbiosis being linked to numerous diseases that may be modifiable through diet, supplementation, or physical activity. Dysbiosis of the gut microbiome has also been implicated in MAFLD and NAFLD, which are the most prevalent liver diseases globally, affecting approximately 35% of the adult population, with this prevalence expected to rise. The gut-liver axis has been extensively studied in relation to MAFLD/NAFLD due to the bidirectional interactions between the gut microbiota and hepatic function. The portal vein, which supplies approximately 70% of the liver's blood flow, facilitates this interaction by connecting the intestines to the liver. Patients with NAFLD/MAFLD typically exhibit increased intestinal permeability compared to healthy individuals, thereby increasing the liver's exposure to gut-derived bacteria, endotoxins, bacterial products, and inflammatory mediators.

Probiotics, defined as live microorganisms that confer health benefits to the host, have been shown in previous studies to enhance the integrity of the intestinal barrier, regulate the gut microbiota, reduce intestinal permeability, and mitigate immune and metabolic disturbances. These effects are particularly relevant in patients with NAFLD/MAFLD, where probiotics have been observed to reduce hepatic steatosis and inflammation-related damage.

Physical exercise, particularly structured programs, has been demonstrated to significantly improve liver function in patients with NAFLD/MAFLD and positively modulate the gut microbiota. Exercise may attenuate the production of reactive oxygen species (ROS) and other oxidative agents in NAFLD by regulating antioxidant enzymes and anti-inflammatory mediators. Additionally, exercise interventions in these patients have been shown to improve blood lipid profiles, including triglycerides, cholesterol, AST, and ALT levels, offering substantial clinical benefits. Although the existing literature predominantly emphasizes aerobic training, this study seeks to compare the effects of resistance training and probiotic supplementation in patients with NAFLD/MAFLD and to assess potential changes in clinical outcomes. Furthermore, the study will explore the influence of baseline ANS and gut microbiota profiles on the patients' responses to these non-pharmacological therapies.

Study population: Patients diagnosed with non-alcoholic or metabolically mediated fatty liver disease (NAFLD/MAFLD), including the inflammatory form (NASH), confirmed by imaging (ultrasound, MRI-PDFF) or histopathological (liver biopsy) methods.

Inclusion criteria:

• Diagnosis of NAFLD/MAFLD or NASH (imaging or histological confirmation of fatty liver disease, e.g., ultrasound, MRI-PDFF, biopsy)
• Age 18-60 years
• Ability to understand the study procedures and provide informed consent.
• Stable clinical condition for at least 3 months prior to study initiation.

Exclusion criteria:

• Lack of fluency in English or Polish
• Significant (structural) limitation of upper and/or lower limb mobility
• Pregnancy or breastfeeding
• Inability to understand instructions
• Shift work
• Participation in any study or research project within the last 3 months
• Participation in an interventional drug study within the last 3 months
• Participants with hepatic steatosis and regular alcohol consumption > 30 g/day
• Individuals with any concomitant liver disease (viral hepatitis, drug-induced liver injury, metabolic/genetic diseases (e.g., Wilson's disease))
• Anticoagulant/antiplatelet therapy, antithrombotic therapy, immunosuppressive medications, prolonged immunosuppression (e.g., recent cytotoxic chemotherapy, HIV infection with CD4 count < 240), antibiotics, corticosteroids, valproic acid, amiodarone, tamoxifen within 3 months prior to study enrollment
• Use of medications such as steroids, methotrexate, metformin
• Use of agents such as vitamin E, omega-3 fatty acids, or medications with evidence of an effect on NAFLD (pioglitazone, GLP-1 analogues, dipeptidyl peptidase IV inhibitors, ursodeoxycholic acid)
• Active or previous history of invasive cancer (excluding curatively treated carcinoma in situ [e.g., cervical] or benign skin cancer), unless complete remission has been achieved
• Regular use of probiotic or prebiotic supplements within 3 months prior to study enrollment
• Known allergy to probiotics
• History of using an alternative diet within 3 months prior to study enrollment or changing diet during study entry
• Previous surgery (bariatric surgery, gastric or intestinal resection)
• Parenteral nutrition (TPN) within the last 6 months
• Insulin therapy
• Uncontrolled diabetes
• Cardiovascular disease (e.g., uncontrolled blood pressure, coronary artery disease, NYHA class III-IV heart failure, severe arrhythmias, orthostatic intolerance)
• Nervous system disorders
• Cognitive impairment and dementia
• Osteoporosis/osteopenia
• Active thyroid disease
• Cushing's syndrome
• Any implanted battery-powered device (e.g., AICD, pacemaker, cardiac rhythm recorder, cochlear implant)

Data would be shared upon a reasonable request from other researches. Requests could be made with a contact Authors after publication of papers on the collected data.