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Which substances besides human metabolites can appear in metabolomic studies of urine?

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Diagram illustrating metabolism with two sections: anabolic reaction on the left shows energy used to build larger molecules from smaller ones, while catabolic reaction on the right shows larger molecules breaking down into smaller molecules with energy released. — Metabolomics In anabolic reactions, a cell uses energy to combine small molecules into larger molecules. In catabolic reactions, molecules are broken down, and energy is released.

In addition to classic human metabolites, metabolomic studies of urine frequently detect a wide array of exogenous and microbial substances. These include:

Dietary components: This category encompasses various food additives and botanical compounds derived from the diet.1
Microbial products: Urine contains substances resulting from the fermentation processes of gut microbes. A notable example is hippuric acid, which is formed when the liver conjugates glycine with benzoic acid released by intestinal bacteria breaking down dietary plant matter.12
Pharmacological agents: A great variety of drugs and their associated metabolic products are commonly measured in urine.31
Unknown substances: Nontargeted metabolomic approaches often identify molecular variables that currently lack known identities.1

The presence of these diverse compounds reflects the complex influence of diet, the microbiome, and environmental exposures on the human metabolic profile.12