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

<p><strong>AIM:</strong> 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).</p> <p><strong>METHODS:</strong> Participants were randomised into either circuit exercise training (EX; <i>n</i> = 13; 3 h/wk without changes in dietary habits), or dietary energy restriction (ER) without changes in structured physical activity (ER; <i>n</i> = 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: <i>n</i> = 10; ER:<i> n</i> = 6).</p> <p><strong>RESULTS:</strong> 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, <i>P</i> = 0.03) but remained unchanged in response to EX (0.10 ± 0.03 mmol/L vs 0.11 ± 0.07 mmol/L,<i> P </i>= 0.39). Basal RQ decreased (<i>P</i> = 0.05) in response to EX, while this change was not significant after ER (<i>P</i> = 0.38). VO_2peak (<i>P </i>< 0.001) and maximal Fat_ox during aerobic exercise (<i>P</i> = 0.03) improved with EX but not with ER (<i>P</i> > 0.05). The increase in β-hydroxybutyrate concentrations was correlated with the reduction in hepatic steatosis (r = -0.56, <i>P</i> = 0.04).</p> <p><strong>CONCLUSION:</strong> 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.</p>