Independent effects of diet and exercise training on fat oxidation in non-alcoholic fatty liver disease

AIM To investigate the independent effects of 6-mo of dietary energy restriction or exercise training on wholebody and hepatic fat oxidation of patients with nonalcoholic fatty liver disease(NAFLD).METHODS Participants were randomised into either circuit exercise training(EX;n = 13;3 h/wk without changes in dietary habits),or dietary energy restriction(ER) without changes in structured physical activity(ER;n = 8).Respiratory quotient(RQ) and whole-body fat oxidation rates(Fatox) were determined by indirect calorimetry under basal,insulin-stimulated and exercise conditions.Severity of disease and steatosis was determined by liver histology;hepatic Fatox was estimated from plasma β-hydroxybutyrate co.ncentrations;cardiorespiratory fitness was expressed as VO2 peak.Complete-case analysis was performed(EX:n = 10;ER:n = 6).RESULTS Hepatic steatosis and NAFLD activity score decreased with ER but not with EX.β-hydroxybutyrate concentrations increased significantly in response to ER(0.08 ± 0.02 mmol/L vs 0.12 ± 0.04 mmol/L,P = 0.03) but remained unchanged in response to EX(0.10 ± 0.03 mmol/L vs 0.11 ± 0.07 mmol/L,P = 0.39).Basal RQ decreased(P = 0.05) in response.to EX,while this change was not significant after ER(P = 0.38).VO_(2peak)(P < 0.001) and maximal Fa_(tox) during aerobic exercise(P = 0.03) improved with EX but not with ER(P > 0.05).The increase in β-hydroxybutyrate concentrations was correlated with the reduction in hepatic steatosis(r =-0.56,P = 0.04).CONCLUSION ER and EX lead to specific benefits on fat metabolism of patients with NAFLD.Increased hepatic Fat_(ox) in response to ER could be one mechanism through which the ER group achieved reduction in steatosis.