The Triglyceride–Glucose Index and Colorectal Adenoma: A CHungcheong Association for the Study of Intestinal Disease (CHASID) Multi-Center Cross-Sectional Study

Background/Objectives: Insulin resistance is increasingly recognized as a cause of colorectal neoplasms, but its measurement requires fasting insulin, which is not routinely available in clinical settings. The triglyceride–glucose (TyG) index, derived from fasting triglyceride and glucose, has emerged as a simple surrogate of insulin resistance. We aimed to evaluate the association of the TyG index with colorectal adenoma, identify a clinically usable cut-off, and examine whether the association is preserved across major subgroups. Methods: We conducted a cross-sectional analysis of 7251 asymptomatic adults who underwent screening colonoscopy and same-day biochemistry at university hospital health care centers in Daejeon and Chungcheong province of South Korea between November 2019 and June 2022. The TyG index was calculated as ln[fasting triglycerides (mg/dL) × fasting glucose (mg/dL)/2]. Multivariable logistic regression was used to estimate odds ratios (ORs) for adenoma; discrimination was evaluated by area under the receiver-operating-characteristic curve (AUC), and the optimal cut-off was identified by Youden’s J. Large adenoma (≥10 mm) was analyzed as a secondary outcome. Results: Among 7251 participants (mean age 54.1 ± 11.2 years; 59.7% male; mean BMI 24.7 ± 3.4 kg/m2), 2402 (33.1%) had at least one colorectal adenoma. Adenoma prevalence rose monotonically across TyG quartiles (Q) (Q1, 26.3%; Q2, 32.0%; Q3, 35.5%; Q4, 38.7%; p for trend <0.001). A 1-standard deviation (SD) increase in TyG index was associated with adenoma prevalence in the fully adjusted model (OR 1.13, 95% confidence interval (CI) 1.06–1.20), and the Q4-versus-Q1 OR was 1.29 (1.09–1.53). The optimal cut-off for adenoma was TyG index = 8.55 (AUC 0.564, sensitivity 59.1%, specificity 50.8%); the association was modestly stronger for large adenoma (AUC 0.585; adjusted OR per 1-SD 1.25, 1.09–1.43). Subgroup analyses showed consistent effects across sex, age, body mass index, hypertension, diabetes, and metabolic-syndrome strata (all p for interaction >0.17). Conclusions: In a large screening cohort, an elevated TyG index was associated with the presence of colorectal adenoma, with a graded dose–response relationship and a modestly more pronounced association for large adenoma. Although discrimination by TyG index alone is too modest to support its use as a stand-alone screening tool, the index may serve as a low-cost adjunct within a multifactorial risk-stratification framework.