Association between bowel movement frequency, stool consistency and MAFLD and advanced fibrosis in US adults: a cross-sectional study of NHANES 2005-2010

BACKGROUND: Although previous studies have established associations between specific gut microbiota (GM) and metabolic dysfunction-associated fatty liver disease (MAFLD), research examining the relationship between functional gastrointestinal symptoms and MAFLD, including advanced fibrosis, remains limited. This study aims to investigate the association between stool consistency, bowel movement frequency (BMF), and the occurrence of MAFLD and advanced fibrosis in U.S. adults. METHODS: This population-based study included 9,928 adults from the 2005-2010 National Health and Nutrition Examination Survey (NHANES), with a mean age of 47.19 ± 16.65 years, comprising 47.7% males and 52.3% females. Weighted logistic regression was used to assess the association between stool consistency, BMF, and MAFLD or advanced fibrosis. A linear trend was assessed by treating BMF categories as continuous variables with ordinal values. The dose-response relationship between BMF and MAFLD was analyzed using restricted cubic splines (RCS) regression. Sensitivity and subgroup analyses were performed to confirm the robustness of the findings. RESULTS: In the RCS regression, no significant nonlinear relationship was observed between BMF and the risk of MAFLD (p-overall 2 BMs/day, respectively, compared to those with once/day (p-trend < 0.001). For stool consistency, hard stools were associated with a decreased risk of MAFLD (OR 0.77; 95% CI 0.62-0.95), whereas loose stools increased the risk (OR 1.37; 95% CI 1.05-1.80), relative to normal stools. A significant interaction between BMF and age was observed. No significant associations were found between stool consistency or BMF and advanced liver fibrosis. Sensitivity analyses confirmed the robustness of these findings. CONCLUSIONS: This cross-sectional study demonstrates that a BMF of 3-6 BMs/week and hard stools are associated with a reduced risk of MAFLD, whereas a BMF of more than once/day and loose stools are linked to an increased risk of MAFLD. Moreover, no significant associations were observed between stool consistency, BMF, and advanced fibrosis among individuals diagnosed with MAFLD. CLINICAL TRIAL NUMBER: Not applicable.