The association between tongue features and tongue coating microbiota and gastrointestinal cancer: a systematic review and meta-analysis

Background: Gastrointestinal (GI) cancers pose a significant health burden, highlighting the need for non-invasive biomarkers. Tongue inspection, a traditional diagnostic method in Chinese medicine, has been increasingly quantified via imaging and microbiome analysis. Objective: This review synthesizes evidence on tongue features and coating microbiota in GI cancer detection. Design: We systematically searched PubMed, EMBASE, Cochrane and Chinese databases until July 2025 for case-control or cohort studies comparing tongue characteristics or microbiota between GI cancer patients and healthy controls. Data were pooled using fixed- or random-effects models. Results: = 4,994) were included. GI cancer patients showed significantly higher rates of abnormal tongue body morphology (OR = 5.33, 95% CI 3.26-8.72), abnormal tongue body color (OR = 17.85, 95% CI 7.01-45.54), abnormal tongue coating texture (OR = 5.98, 95% CI 4.02-8.91) and abnormal tongue coating color (OR = 3.24, 95% CI 2.00-5.26) versus controls. Although α-diversity did not differ, certain taxa (e.g. Actinobacteria, Prevotella_7) were reduced in cancer patients. Subgroup analyses by cancer type showed generally consistent directions of association for abnormal tongue manifestations in gastric, colorectal and esophageal cancers, despite significant heterogeneity. Conclusion: Abnormal tongue features and specific microbial shifts are associated with GI cancers, suggesting potential non-invasive tools for early detection. However, due to heterogeneity and methodological limitations, further large-scale prospective studies are needed for validation.