For both diseases the progression of liver damage is in close correlation with the lifestyle of patients (eg., nutrition, physical activity, ingestion of alcohol, etc.). In fact, it was shown that feeding imbalances may have implications in altering the normal immune functions of the subjects, suggesting that the metabolic and the immune systems are closely related to each other. Although it is well known the negative role of obesity on the progression of NAFLD and HCV liver diseases, the pathogenic mechanism underlying the alterations related to the immune response is not yet fully understood. Insulin resistance, altered lipid metabolism, lipid peroxidation, oxidative stress and mitochondrial alterations are pathogenic mechanisms that induce liver damage and its progression, both in NAFLD and in HCV infection.