Bile Acids
Plain-English definitions of microbiome research vocabulary — the terms you'll see across articles, testing services, and probiotic claims.
Compounds produced by the liver to aid fat digestion. Primary bile acids are modified by gut bacteria into secondary bile acids, which have signalling functions affecting metabolism, immune regulation, and gut motility. The microbiome's role in bile acid metabolism is a key mechanism linking gut bacteria to metabolic health.
Related terms
Metabolome
The complete set of small-molecule metabolites (such as short-chain fatty acids, amino acids, vitamins, and bile acids) found within a biological system. The gut metabolome — largely produced or modified by the microbiome — provides functional information about what gut bacteria are actually doing, beyond simply which species are present.
Firmicutes
The largest bacterial phylum in the human gut, encompassing diverse genera including Lactobacillus, Clostridium, Faecalibacterium, and Ruminococcus. Many important SCFA producers belong to this phylum. An elevated Firmicutes-to-Bacteroidetes ratio has been associated with obesity in some studies, though the relationship is complex and inconsistent.