The Effects Of Combined Training On Hepatic Fat Content And The Role Of Metabolic Flexibility In Individuals With Non-alcoholic Fatty Liver Disease

Objective:Non-alcoholic fatty liver disease（NAFLD）is a global public health problem,affecting approximately 1/4 of adults worldwide.Exercise intervention is a primary approach for treating NAFLD,and it is necessary to explore the effects of different forms of exercise on NAFLD.Metabolic flexibility（MF）may play a significant role in this context,and further investigation is needed to explore the relationship between MF,exercise,and hepatic fat content（HFC）in the liver.Therefore,the aim of this study is to investigate the relationship between MF and HFC in NAFLD,and compare the effects of resistance exercise combined with moderate-intensity continuous exercise or high-intensity interval exercise on HFC and clinical blood parameters in NAFLD patients,and analyze the role of MF in reducing HFC through exercise.Method:Study 1:A total of 30 NAFLD patients were recruited to evaluate metabolic flexibility by measuring the difference in respiratory quotient（RQ）between sedentary and moderate-intensity exercise(60%VO_2peak)（ΔRQ=RQ exercise-RQ sedentary）using metabolic cart and were divided into a high metabolic flexibility group（HMF）and a low metabolic flexibility group（LMF）based on the median value ofΔRQ.Hepatic fat content（HFC）and abdominal subcutaneous and visceral fat content were assessed using magnetic resonance imaging,and clinical blood parameters were measured using standard methods.T-test and correlation analysis were used to compare the differences in HFC and clinical blood indicators between different groups and analyze the relationship between metabolic flexibility and HFC and clinical blood indicators.Study 2:A total of 53 NAFLD patients were recruited,and the HFC and clinical blood parameter measurement methods were the same as those in study 1.All subjects were randomly stratified and divided into a control group（CON）,a resistance training combined with high-intensity interval training group（R+H）,and a resistance training combined with moderate-intensity continuous exercise group（R+M）in a 1:1:1 ratio.The CON group continued their daily lifestyle,while the R+H and R+M groups underwent resistance training combined with high-intensity interval exercise or moderate-intensity continuous exercise three times per week for 12 weeks.The metabolic indicators of the NAFLD patients were evaluated in the same way as at baseline after the intervention.Paired samples t-test and analysis of variance were used to compare the differences within and between groups before and after the intervention.Study 3:A total of 34 NAFLD patients were selected from those who underwent baseline testing and intervention in experiment 2,including 10 in the CON group,12in the R+H group,and 12 in the R+M group.Fasting and 2-hour postprandial plasma samples were collected from the subjects and subjected to untargeted metabolomics analysis.The different metabolites between high-fat diet before and after,before and after exercise intervention,and different exercise modes were screened using fold change（FC≥1.5）and false discovery rate（FDR≤0.05）,and the relationship between HFC and different metabolites before and after high-fat diet was analyzed using Pearson correlation analysis.The content of different metabolites related to HFC in a deficient state was compared using a general linear model with adjustment for age,sex,and weight.Result:Study 1:The average liver fat content in the LMF group was 8.29%higher（95%CI:4.65,11.93）than that in the HMF group,but there was no statistically significant difference in the visceral and subcutaneous fat content.The LMF group had a higher fasting glucose level than the HMF group（1.75 mmol/L,p=0.046）,as well as higher levels of low-density lipoprotein cholesterol（p<0.001）,alanine aminotransferase（p=0.017）,and aspartate aminotransferase（p=0.031）.Multiple linear regression analysis showed that liver fat was negatively correlated with resting fatty acid oxidation（p=0.025）and positively correlated with exercise fatty acid oxidation（p=0.039）after adjusting for age,sex,BMI,and VO_2peak.Study 2:After 12 weeks of exercise intervention,the R+H group reduced liver fat content by approximately 5.51%（p=0.001）,while the R+M group reduced liver fat by approximately 5.02%（p=0.002）,with no statistically significant difference between the exercise groups.The R+H group significantly improved insulin sensitivity in NAFLD patients,including fasting insulin（-28.5 pmol/L,p=0.008）,HOMA-IR（-8.8,p<0.05）,QUICKI（0.003,p<0.05）,and Adipose-IR（-20.3,p<0.05）,and significantly reduced alanine aminotransferase（-22.9 U/L,p=0.014）,with a trend towards greater reduction than the R+M group（p=0.078）.The R+M group significantly reduced insulin AUC（-118.5,p=0.026）.Study 3:In individuals with NAFLD,the main differential metabolites between postprandial and fasting states are metabolites associated with lipid metabolism.After exercise intervention,there is an upregulation trend of lipid metabolism-related metabolites in response to high-fat diet stimulation.The resistance exercise combined with high-intensity interval training has a greater impact on lipid metabolism under high-fat diet stimulation compared to the combination of resistance exercise and moderate-intensity continuous exercise,and there is a negative correlation between the relevant metabolic products and high-fat diet-induced changes.ConclusionThere is a negative correlation between MF and HFC in NAFLD patients,indicating that NAFLD patients with higher MF have lower HFC.Furthermore,NAFLD patients with higher MF is better in glucose and lipid metabolism indicators,as well as liver function indicators.The combination of resistance exercise and high-intensity interval exercise produces similar reductions in liver fat content as moderate-intensity continuous exercise but in a shorter time and with lower energy expenditure.This combined exercise approach has a positive impact on a broader range of clinical glucose and lipid metabolism indicators and leads to better improvement in liver function indicators compared to the combination of resistance exercise and moderate-intensity continuous exercise.The results from non-targeted metabolomics reveal that the combination of resistance exercise and high-intensity interval exercise has a greater positive effect on lipid metabolism under a high-fat diet challenge in NAFLD.This effect is negatively correlated with changes in HFC,which explains why this combined exercise approach produces similar reductions in HFC as the combination of resistance exercise and moderate-intensity continuous exercise,despite the shorter exercise duration and lower energy expenditure.