Meta-analysis finds exercise training reduces intrahepatic lipids and improves metabolic markers in NAFLD

This systematic review and meta-analysis examined the effects of exercise training on intrahepatic lipid content and metabolic markers in adults with nonalcoholic fatty liver disease (NAFLD). The analysis pooled data from 1,880 participants across multiple studies. The population specifically comprised adults with and without NAFLD, though the exact clinical characteristics and baseline severity of liver disease were not detailed in the provided data. The setting of the included studies was not reported.

The intervention evaluated was exercise training, which encompassed several modalities: high-intensity interval training (HIIT), aerobic training, combined aerobic and resistance training, and resistance training. The comparator groups were either nonexercise control groups or groups receiving other types of exercise training, allowing for assessment of exercise versus no exercise and comparisons between different exercise regimens. Specific details on exercise dosing, such as frequency, intensity, duration, and total program length, were not provided in the input data.

The primary outcome was intrahepatic lipid content. Exercise training was significantly more effective than nonexercise controls at reducing intrahepatic lipids, with a standardized mean difference (SMD) of -0.33 (p = 0.001). This represents a small-to-moderate effect size favoring the exercise interventions.

Key secondary outcomes also showed significant benefits. For glucose homeostasis markers, exercise training led to greater reductions in fasting blood glucose (weighted mean difference [WMD]: -2.27 mg/dL, p = 0.007), fasting insulin (SMD: -0.16, p = 0.02), and glycated hemoglobin (SMD: -0.13, p = 0.03) compared to nonexercise groups. Regarding liver function enzymes, exercise was associated with greater reductions in alanine aminotransferase (ALT; WMD: -3.72 U/L, p = 0.001) and aspartate aminotransferase (AST; WMD: -3.51 U/L, p = 0.02). However, the analysis found no significant differences between groups for the outcome of insulin resistance.

Safety and tolerability findings were not reported in the provided data. There is no information on adverse events, serious adverse events, discontinuation rates, or general tolerability of the various exercise interventions across the pooled studies.

These results align with and consolidate evidence from prior smaller trials and reviews suggesting that physical activity is beneficial for reducing liver fat and improving metabolic parameters in NAFLD. The finding of no significant effect on insulin resistance, however, contrasts with some individual studies and highlights the complexity of measuring this outcome and the variable responses to exercise.

Key methodological limitations stem from the nature of meta-analyses. The quality and risk of bias depend entirely on the constituent studies, which were not described. Potential biases include publication bias, heterogeneity in exercise protocols and intensities across studies, and variability in how outcomes like intrahepatic lipids were measured (e.g., MRI-PDFF, MRS, biopsy). The lack of reported safety data is a significant limitation for clinical application. Furthermore, the analysis could not determine which specific exercise modality (HIIT, aerobic, resistance, or combined) was most effective, as comparisons between exercise types were not detailed.

The clinical implication is that this meta-analysis provides pooled, quantitative evidence supporting the integration of structured exercise training into the lifestyle management plan for patients with NAFLD. It demonstrates benefits beyond liver fat reduction to include improvements in glycemic control and liver enzymes. For practice, this reinforces current guideline recommendations promoting physical activity. However, clinicians should note that the evidence does not point to a single superior exercise type and that the absolute reductions in liver enzymes, while statistically significant, are modest.

Several important questions remain unanswered. The optimal exercise prescription—including the most effective type, required intensity, frequency, and duration—for NAFLD management is still unclear. The long-term sustainability of these benefits and their impact on hard clinical endpoints like progression to steatohepatitis (NASH), cirrhosis, or liver-related mortality are unknown. The safety profile of different exercise regimens in a NAFLD population, particularly those with comorbidities, was not reported and requires investigation. Finally, how exercise compares or synergizes with pharmacological therapies for NAFLD is a critical area for future research.