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 Sixteen studies (n = 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.