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Background and Aims: Bile acids (BA) are vital regulators of metabolism. BAs are AQ6 secreted in the small intestine, reabsorbed, and transported back to the liver, where they can modulate metabolic functions. There is a paucity of data regarding the portal BA composition in humans. This study aimed to address this knowledge gap by investigating portal BA composition and the relation with peripheral and fecal BA dynamics in conjunction with the gut microbiome., Approach and Results: Thirty-three individuals from the BARIA cohort were included. Portal plasma, peripheral plasma, and feces were collected. BA and C4 levels were measured employing mass spectrometry. FGF19 was measured using ELISA. Gut microbiota composition was determined through metagenomics analysis on stool samples. Considerable diversity in the portal BA composition was observed. The majority (n = 26) of individuals had a 9-fold higher portal than peripheral BA concentration. In contrast, 8 individuals showed lower portal BA concentration compared with peripheral and had higher levels of unconjugated and secondary BA in this compartment, suggesting more distal origin. The altered portal BA profile was associated with altered gut microbiota composition. In particular, taxa within Bacteroides were reduced in abundance in the feces of these individuals., Conclusions: Characterization of the portal BA composition in relation to peripheral and fecal BA increased insight into the dynamics of BA metabolism in individuals with obesity. Peripheral BA composition was much more diverse due to microbial metabolism. About 24% of the portal samples was surprisingly low in total BA; the underlying mechanism requires further exploration., (Copyright © 2024 American Association for the Study of Liver Diseases.)