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 (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 beta-hydroxybutyrate concentrations; cardiorespiratory fitness was expressed as VO2peak. 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. Beta-hydroxybutyrate concentrations increased significantly in response to ER (0.08 +/- 0.02 mmol/L versus 0.12 +/- 0.04 mmol/L, p = 0.03) but remained unchanged in response to EX (0.10 +/- 0.03 mmol/L versus 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). VO2peak (p < 0.001) and maximal Fatox during aerobic exercise (p = 0.03) improved with EX but not with ER (p > 0.05). The increase in beta-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 Fatox in response to ER could be one mechanism through which the ER group achieved reduction in steatosis.

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