Background Insulin resistance (IR) increases vascular risk in individuals with Type 1 Diabetes (T1D). We aimed to investigate the relationship between dietary intake and IR, as well as vascular biomarkers in T1D. Methods Baseline data from three randomised controlled trials were pooled. Estimated glucose disposal rate (eGDR) was used as an IR marker. Employing multivariate nutrient density substitution models, we examined the association between macronutrient composition and IR/vascular biomarkers (tumour necrosis factor-α, fibrinogen, tissue factor activity, and plasminogen activator inhibitor-1). Results Of the 107 patients, 50.5% were male with mean age of 29 ± 6 years. Those with lower eGDR were older with a longer diabetes duration, higher insulin requirements, and an adverse vascular profile (p < 0.05). Patients with higher degrees of IR had higher total energy intake (3192 ± 566 vs. 2772 ± 268 vs. 2626 ± 395 kcal/d for eGDR < 5.1 vs. 5.1–8.6 vs. ≥ 8.7 mg/kg/min, p < 0.001) and consumed a higher absolute and proportional amount of fat (47.6 ± 18.6 vs. 30.4 ± 8.1 vs. 25.8 ± 10.4%, p < 0.001). After adjusting for total energy intake, age, sex, and diabetes duration, increased carbohydrate intake offset by an isoenergetic decrease in fat was associated with higher eGDR (β = 0.103, 95% CI 0.044–0.163). In contrast, increased dietary fat at the expense of dietary protein intake was associated with lower eGDR (β = − 0.119, 95% CI − 0.199 to − 0.040). Replacing fat with 5% isoenergetic amount of carbohydrate resulted in decreased vascular biomarkers (p < 0.05). Conclusion Higher fat, but not carbohydrate, intake is associated with increased IR and an adverse vascular profile in patients with T1D.