Associations between physical activity and dietary live microbe intake with non-alcoholic fatty liver disease: findings from the NHANES, 2007–2018

Background: Physical activity (PA) and dietary live microbe intake protect against non-alcoholic fatty liver disease (NAFLD) by improving insulin resistance, yet whether they act through shared metabolic pathways - such as those reflected by the triglyceride-glucose (TyG) index - remains unclear. We aimed to investigate the independent and combined associations of PA and dietary live microbe intake with NAFLD and to explore the mediating effect of the TyG index. Methods: We retrieved data from the National Health and Nutrition Examination Survey 2007-2018, which defined NAFLD by the US fatty liver index, PA using the self-reported Global Physical Activity Questionnaire, and dietary live microbe intake levels through 24-hour dietary recall data. We assessed individual and joint effects of PA and dietary live microbe intake via weighted multivariate logistic regression models and explored the mediating effect of the TyG index via causal mediation analysis. Results: Our analysis encompassed 10 387 participants. The multivariate-adjusted odds ratios (ORs) were 0.84 (95% confidence interval (CI) = 0.72-0.99; P = 0.040) for NAFLD patients with sufficiently high PA and 0.78 (95% CI = 0.66-0.92; P = 0.003) for those with relatively high dietary live microbe intake. In the joint analysis, individuals with sufficiently high PA and higher dietary live microbe intake had the lowest risk of NAFLD (OR = 0.68; 95% CI = 0.56-0.84, P < 0.001), particularly those aged <65 years. The TyG index mediated 40.80% of the association between PA and NAFLD, as well as 28.44% of the association between dietary live microbe intake and NAFLD. Conclusions: Our findings suggest that public health strategies promoting both regular physical activity and consumption of foods rich in live microbes may offer a synergistic approach for NAFLD prevention, particularly in adults under 65 years of age.