Relationships among the triglyceride-glucose index, its changes, and the development of metabolically obese normal weight are strengthened by increased visceral fat area.

Background: Metabolically obese normal weight (MONW), obesity with a normal body mass index, is often neglected due to the seemingly normal weight but has a high risk of metabolic diseases. This study aimed to assess associations among the triglyceride-glucose (TyG) index, its changes (∆TyG index), and metabolically normal, normal weight (MNNW) to MONW transition via a population-based cohort study.

Methods: Participants aged 40-65 years in 15 Chinese communities were recruited. A total of 530 participants [mean age: 53.00 (48.00-58.00) years; 346 (65.3%) female participants] with complete data on anthropometry, metabolic indicators, abdominal visceral fat area (VFA), and a normal body mass index (BMI) (18.5 ≤ BMI < 24) were included in the cross-sectional analysis. In total, 253 participants [mean age: 53.00 (48.00-58.00) years; 171 (67.6%) female participants] who had follow-up and maintained a normal BMI were included in the follow-up analysis. MONW was defined as two or more abnormal metabolic components but with a normal BMI. Multivariate logistic regression, Cox proportional hazards regression, and restricted cubic spline regression were used to assess associations among the TyG index, ∆TyG index, and MONW-MONW and MNNW-MONW transition.

Results: An incrementally higher risk of MONW was observed with the increasing TyG index quartiles in the cross-sectional analysis. The adjusted odds ratio (OR) in the TyG index quartile 4 was 31.81 (95% CI 11.47-88.20) for MONW, and there was a significant MONW risk for TyG >9.04. A positive linear association between the ∆TyG index (p trend = 0.001) instead of the TyG index (p for non-linearity = 0.034) and MNNW-MONW transition was observed. The adjusted hazard ratio (HR) in the TyG index quartile 3 was 2.35 (95% CI 1.02-5.41), and in the ∆TyG index quartile 4 was 3.60 (95% CI 1.48-8.79) for MNNW-MONW transition. Subgroup analyses revealed the correlations among the TyG index, ∆TyG index, and MONW-MONW and MNNW-MONW transition were more evident in individuals with larger VFA, and similar results were obtained in sensitivity analysis.

Conclusion: The elevated TyG index and ∆TyG index were associated with higher risks of MONW-MONW and MNNW-MONW transition, and these associations were strengthened by VFA. In addition, the ∆TyG index may be a better indicator for predicting MNNW-MONW transition.