Ulvan Acts as a Prebiotic Polysaccharide Enhancing the Production of Indoles and Short-Chain Fatty Acids In Vitro: A Metabolomics Study
A 48-hour lab-based fermentation study investigated the prebiotic potential of ulvan, a sulfated polysaccharide extracted from Ulva lactuca L. (a species of green seaweed), using fecal samples from four healthy adult donors to simulate what happens when ulvan reaches the colon. Researchers compared ulvan against inulin, and a no-fiber control to isolate the effects of ulvan specifically. Both targeted and untargeted metabolomics were used to capture the full range of metabolic activity produced during fermentation.
The results revealed that ulvan significantly stimulated production of short-chain fatty acids (SCFAs), particularly acetic acid, reaching levels statistically comparable to inulin by 24 and 48 hours. Ulvan also selectively shifted tryptophan metabolism toward the production of indole-3-propionic acid (IPA) and indole-3-acetic acid (IAA) — metabolites associated with intestinal barrier protection and immune regulation, while reducing the accumulation of less favorable byproducts like tryptamine and indole. Broader metabolic profiling also identified increases in cyclic proline dipeptides linked to beneficial microbial groups including Bacteroides, Bifidobacterium, and Lactobacillus species. These findings support the classification of ulvan as a fermentable prebiotic fiber capable of selectively promoting beneficial metabolic activity.
The study also highlights that individual responses varied across donors, reflecting how baseline microbiome composition can influence prebiotic outcomes, which is a pattern consistent with what the field sees across fiber research broadly. Because this was a lab model, it can’t fully replicate the complexity of the human gut, and the researchers did not sequence the microbiome, so the specific bacteria driving these effects weren’t directly identified. Future studies should combine in vivo trials with microbiome sequencing to confirm these mechanisms in humans. Overall, this research positions ulvan as a promising functional ingredient that supports gut health not only by fueling beneficial bacteria, but by directing microbial activity toward the production of metabolites with real biological significance.
