Association of diet with glycated hemoglobin during intensive treatment of type 1 diabetes in the Diabetes Control and Complications Trial

Persons with type 1 diabetes have received widely varying dietary advice based on putative effects on glycemic control. The objective was to determine whether diet composition was associated with subsequent glycated hemoglobin (Hb A1c) concentrations during intensive therapy for type 1 diabetes. We examined associations between quantiles of dietary intake and Hb A1c adjusted for age and sex in 532 intensively treated participants in the Diabetes Control and Complications Trial (DCCT) who had complete dietary data through 5 y of follow-up. Multivariate macronutrient density linear regression models tested the association of Hb A1c at year 5 with macronutrient composition and were adjusted for age, sex, exercise, triglyceride concentration, body mass index (BMI), baseline Hb A1c, and concurrent insulin dose. Higher insulin dose, lower carbohydrate intake, and higher saturated, monounsaturated, and total fat intakes were associated with higher Hb A1c concentrations at year 5. In age- and sex-adjusted multivariate macronutrient models, substitution of fat for carbohydrate was associated with higher Hb A1c concentrations (P = 0.01); this relation remained significant after adjustment for exercise level, serum triglycerides, and BMI (P = 0.02) but was no longer significant (P = 0.1) after adjustment for baseline Hb A1c and concurrent insulin dose. Among intensively treated patients with type 1 diabetes, diets higher in fat and saturated fat and lower in carbohydrate are associated with worse glycemic control, independent of exercise and BMI.