Ilias Attaye,1,2,5,* Beverley Beynon-Cobb,1,3,5 Panayiotis Louca,1 Ana Nogal,1 Alessia Visconti,1 Francesca Tettamanzi,1 Kari Wong,4 Gregory Michellotti,4 Tim D. Spector,1 Mario Falchi,1 Jordana T. Bell,1 and Cristina Menni1,6,7,*

Chronic kidney disease (CKD) is a major public health burden, with dietary acid load (DAL) and gut microbiota playing crucial roles. As DAL can affect the host metabolome, potentially via the gut microbiota, we cross -sectionally investigated the interplay between DAL, host metabolome, gut microbiota, and earlystage CKD (TwinsUK, n = 1,453). DAL was positively associated with CKD stage G1 -G2 (Beta (95% confidence interval) = 0.34 (0.007; 0.7), p = 0.046). After adjusting for covariates and multiple testing, we identified 15 serum, 14 urine, 8 stool, and 7 saliva metabolites, primarily lipids and amino acids, associated with both DAL and CKD progression. Of these, 8 serum, 2 urine, and one stool metabolites were found to mediate the DAL-CKD association. Furthermore, the stool metabolite 5-methylhexanoate (i7:0) correlated with 26 gut microbial species. Our findings emphasize the gut microbiota's therapeutic potential in countering DAL's impact on CKD through the host metabolome. Interventional and longitudinal studies are needed to establish causality.