Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide. The composition of the diet, especially quality of dietary fat, contributes to the susceptibility to hepatic lipid accumulation. Saturated fatty acids (SFA), but not polyunsaturated fatty acids (PUFA) increases intrahepatic triglycerides with and without concomitant weight gain. Therefore, the modification of dietary fat quality is the key dietary approach for the prevention of NAFLD.~PNPLA3 rs738409 (I148M) variant is associated with hepatic liver accumulation and chronic liver diseases including NAFLD. It has been shown that obesity augments genetic risk but studies investigating the interaction of PNPLA3 rs738409 risk variant and diet are scarce. Therefore, the aim is to investigate the effect of dietary fat quality modification (high unsaturated fat vs. high SFA) on liver fat and lipid and glucose metabolism in participants with different variants (CC or GG) of the PNPLA3 gene.~The investigators will conduct the randomized controlled 12-week dietary intervention trial in participants with different homozygous PNPLA3 variants (CC or GG). The primary outcome of the intervention is in the amount of liver fat measured by nuclear magnetic resonance imaging (MRI). Altogether 140 homozygous participants (PNPLA3 rs738409 CC and GG) will be recruited from the Metabolic Syndrome in Men (METSIM) study. The inclusion criteria include BMI < 35 kg/m2 and age < 75 years. The main exclusion criteria include diabetes, acute illness, or current evidence of acute or chronic inflammatory or infective diseases.~Dietary guidance in the intervention group is based on the Nordic and Finnish nutrition recommendations with an emphasis on the quality of dietary fat. The aims for the intake of fatty acids will be SFA < 10 % of energy intake (E%) and mono- and polyunsaturated fatty acids (UFA) >2/3 of the total fat intake.~The diet of the control group corresponds to the average nutrient intake in the Nordic countries, i.e. the intake of SFA about 15 E% and the proportion of UFA about 50 % of total fat intake.
PNPLA3 rs738409 (I148M) variant is associated with hepatic liver accumulation and chronic liver diseases including non-alcoholic fatty liver disease. It has been shown that obesity augments genetic risk but studies investigating the interaction of PNPLA3 rs738409 risk variant and diet are scarce. The aim is to investigate the effect of dietary fat quality modification in participants with different variants of the PNPLA3 gene (rs738409). The primary outcome is the change in liver fat measured by magnetic resonance imaging in the randomized controlled 12-week dietary intervention trial.