The trials included in our review showed that the use of probiotics, prebiotics and synbiotics were related to reduction in BMI, total fat percentage, total cholesterol, triglycerides, fasting insulin, LPS, HOMA, TNF-α, IL-6, liver injury (AST, ALT, liver stiffness, fibrosis index, intracellular lipids, NAFLD and NASH scores), and Clostridia and Erysipelotrichia classes. The gene discussed is INS; the disease is metabolic dysfunction-associated steatohepatitis.