Exploring Blastocystis and Gut Health: A Pilot Investigation of Microbiome and Metabolomic Signatures in a UK Cohort

Blastocystis is a common protistan coloniser of the human gut, yet its role in health and disease remains unclear. While some studies have linked it to gastrointestinal (GI) symptoms, growing evidence suggests an association with microbial diversity and gut health. This pilot study investigated the prevalence, subtype distribution, and ecological associations of Blastocystis in South East England, and explored its relationship with gut microbiota composition and metabolic profiles, particularly in individuals with or without irritable bowel syndrome (IBS) or ulcerative colitis (UC). We analysed stool samples from 46 participants using qPCR and sequencing to identify Blastocystis subtypes, 16S rRNA gene sequencing to characterise bacterial communities, and 1H NMR spectroscopy to profile the faecal metabolome. Blastocystis was detected in 47.8% of individuals, with subtypes ST1 to ST4 being the most frequently identified. Alpha diversity was higher in Blastocystis-positive individuals, significantly so in IBS cases. While Blastocystis status did not alter overall microbial or metabolomic beta diversity substantially, disease status (IBS/UC) did. Notably, several Blastocystis-associated taxa were negatively correlated with leucine and kynurenine metabolites implicated in inflammation and GI dysfunction. Leucine was positively associated with IBS status, while kynurenine is a known pro-inflammatory product of tryptophan metabolism. These correlations suggest that Blastocystis colonisation may reflect or contribute to gut environments with lower inflammatory potential. This study highlights the need for larger, longitudinal and subtype-resolved investigations to clarify the ecological and functional roles of Blastocystis in the gut microbiome. Our findings support the growing view that Blastocystis, particularly certain subtypes, may be more indicative of gut health than disease.