Associations of bowel movements and stool types with risk of chronic kidney disease

The gut-kidney axis is increasingly recognized in chronic kidney disease (CKD) pathophysiology. Although stool frequency and consistency reflect gut microbiome status, their association with CKD remains underexplored. This study aimed to examine the relationship between bowel habits and CKD risk. In this cross-sectional analysis of 11,760 adults from National Health and Nutrition Examination Survey 2005 to 2010, stool frequency (weekly) and consistency (Bristol Stool Form Scale) were assessed. CKD was defined as estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73m2 and/or urine albumin-to-creatinine ratio (uACR) ≥ 30 mg/g. Weighted logistic regression adjusted for multiple confounders was used; subgroup and mediation analyses were performed. Diarrhea-like stool (Bristol Stool Form Scale types 6/7) was independently associated with higher CKD risk (odds ratio [OR] = 1.57, 95% confidence interval [CI]: 1.14-2.27), consistent across eGFR < 60 (OR = 1.42, 95% CI: 1.01-1.99) and uACR ≥ 30 mg/g (OR = 1.55, 95% CI: 1.03-2.23). Mediation analysis indicated that systemic inflammation (C-reactive protein) explained 10.1%, 8.5%, and 15.3% of these associations for eGFR decline, elevated uACR, and overall CKD, respectively. Subgroup analyses supported robustness across demographic and clinical strata. Bowel movement frequency was not significantly associated with CKD. Diarrhea-like stool consistency, partly mediated by systemic inflammation, is associated with increased CKD risk.