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 whole-body and hepatic fat oxidation of patients with non-alcoholic 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 (Fat(ox)) were determined by indirect calorimetry under basal, insulin-stimulated and exercise conditions. Severity of disease and steatosis was determined by liver histology; hepatic Fat(ox) was estimated from plasma β-hydroxybutyrate concentrations; cardiorespiratory fitness was expressed as VO(2peak). 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 Fat(ox) 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.