Study of the Efficacy and Safety of Nicotinamide in Patients With Liver Fibrosis (NICOFIB)

Inclusion Criteria: * Patients aged between 18 and 85 years. * Diagnosis of non-alcoholic fatty liver disease (NAFLD) by their referring physicians (NAFLD defined as the presence of hepatic steatosis and in the absence of significant alcohol consumption, having excluded other liver diseases). * BMI between 27-40 kg/m2. * Fibroscan® value greater than 9.2 kPa, obtained within the last 6 months prior to the start of the study. Exclusion Criteria: * Patients with any medical condition or illness that, in the opinion of the investigator, could interfere with the study results and/or affect the patients' ability to participate or complete the study. * History of clinically significant heart disease (ejection fraction \<40% \[normal range 50-70%\], heart failure defined as New York Heart Association \[NYHA\] Class \> 2; clinically significant congenital or acquired valvular disease; symptomatic coronary artery disease such as myocardial infarction or angina, history of unstable arrhythmias, history of atrial fibrillation). * Decreased renal function (estimated glomerular filtration rate \<45 mL/min/1.73 m2, calculated using the CKD-EPI formula) at screening. * Alcohol consumption exceeding 30 g/day in men or 20 g/day in women. * Patients with significant impairment of liver function in the selection analysis defined as repeated values of AST, ALT, and bilirubin \> 3 times the upper limit of normal. * Positive for hepatitis B surface antigen or hepatitis C antibodies. * Patients with hepatocellular carcinoma. * Patients with liver cirrhosis (Fibroscan® \> 18, compatible biopsy, or those who have experienced decompensations of cirrhosis). * Patients diagnosed with human immunodeficiency virus (HIV). * Patients with hypersensitivity or a history of severe allergies to NAM or excipients used in the preparation of capsules (NAM and placebo). * Patients with iodinated contrast allergy. * History or evidence of an autoimmune disorder considered clinically significant by the investigator or requiring systemic, chronic use of systemic corticosteroids or other immunosuppressants. * Patients on treatment with hepatotoxic drugs (amiodarone, immunosuppressants, ART, antituberculosis drugs, corticosteroids, etc.). * Patients consuming narcotic and psychotropic substances with hepatotoxic effects. * Individuals with incapacitating diseases or cognitive impairment. * Institutionalized patients or those without a fixed address. * Principal investigator's discretion in case of indications of low adherence to the trial or follow-up visits. * Individuals with a life expectancy of less than 12 months. * Patients participating in another interventional clinical trial, excluding observational/natural history studies, at the start of the study or within the last 30 days before the start of the study. * Previous use of vitamin B3 (NAM), with abstinence required for at least 3 months before screening. * Pregnant women as determined by a positive high-sensitivity serum or urine pregnancy test (minimum sensitivity of 25 IU/L or equivalent units of hCG) within 24 hours prior to screening, dosing, or completion of the study. Women of childbearing potential (WOCBP) will undergo a pregnancy test (serum or urine) 24 hours prior to screening, dosing, or completion of the study. Such participants must use a highly effective contraceptive method, such as combined hormonal contraceptives or intrauterine device (IUD), in accordance with the Clinical Trial Facilitation Group, throughout the entire study. * Breastfeeding women. * Patients undergoing treatment/supplementation with vitamin E. * Patients receiving probiotics. * Patients on the waiting list for bariatric surgery in the next 12 months. * Patients undergoing treatment with drugs that may have an effect on the progression of liver disease. * Drugs for the treatment of T2DM with effects on NAFLD (GLP-1 analogs, thiazolidinediones such as pioglitazone) initiated within 6 months before the study start. * Drugs for the treatment of T2DM with effects on intestinal microbiota (metformin, α-GI inhibitors, DPP-4 inhibitors, and SGLT-2 inhibitors) initiated within 6 months before the study start. * Patients who do not sign the informed consent. * Patients with contraindications to the contrast agent to be used in imaging tests.