BACKGROUND/OBJECTIVES: Chronotype and ultra-processed food (UPF) intake are individually associated with metabolic risk, but their combined effect remains unclear. This study examined the interaction between chronotype and UPF intake in relation to insulin resistance, assessed by the triglyceride-glucose (TyG) index. SUBJECTS/METHODS: Data were obtained from 542 adults in the Gangwon Obesity and Metabolic Syndrome (GOMS) Study. Chronotypes were classified into morning, intermediate, and evening types using Morningness-Eveningness Questionnaire-based clustering. UPF intake was assessed using a food frequency questionnaire and classified according to the Korean-adapted NOVA classification system. Intake was expressed as a percentage of total energy and divided into quartiles. General linear models were used to examine the interaction between chronotype and UPF intake in relation to the TyG index, with adjustments for relevant covariates. An additional analysis examined the association between TyG quartiles and diabetes prevalence. RESULTS: A significant interaction between UPF intake and chronotype was observed only in the evening-type group ( = 0.043). In this group, TyG values were significantly higher in Q3 and Q4 compared to Q1 ( = 0.005). The TyG index also varied significantly across chronotypes and UPF intake quartiles ( = 0.005 and = 0.046, respectively). The odds of diabetes increased across TyG quartiles, with ORs of 3.52 (Q3) and 5.41 (Q4) compared to Q1. CONCLUSION: The association between UPF intake and the TyG index varied by chronotype, with evening types showing greater vulnerability. These findings suggest that biological rhythms may modify the metabolic impact of diet, highlighting the need for personalized prevention strategies.