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Background: It has been suggested that dietary freedom in functional insulin therapy may be detrimental to glycemic control in type 1 diabetes. This study evaluates the effect of carbohydrate intake on glycemic control and postprandial blood glucose concentrations. Methods: Insulin pump data from 148 adults with type 1 diabetes, trained in functional insulin therapy, using pumps for ≥6 months, with ≥2 weeks of consecutive downloaded data, ≥80% use of a bolus calculator, ≥3 capillary blood glucose tests/day, and a concurrent HbA1C, were analyzed. More detailed periprandial data (pre- and postmeal glucose, carbohydrate intake, insulin bolus) were collected from a subset of 105 downloads (3495 meals). Results: Mean (± SD) age of contributors was 43 ± 13 years, HbA1C 7.84% ± 0.93 (62.19 mmol/mol); daily carbohydrate intake 166 ± 71 g. HbA1C reduced with increased meals/day ( r = –.370, P < .0005) and increased with mean carbohydrate content/meal ( r = .198, P = .043). However, total daily carbohydrate intake had a weak but significant negative association with HbA1C ( r = –.181, P = .027). There was no association between standard deviation of carbohydrate intake and HbA1C ( r = .021, P = .802) or between meal carbohydrate content and postprandial change in blood glucose ( r = –.004, P = .939) for meals with early postprandial (1-3 hours; n = 390) readings. There was a weak positive correlation ( r = .184, P = .008) between meal carbohydrate content and late (4-7 hours; n = 390) postprandial readings. Discussion: With appropriate training, patients using insulin pumps can accommodate a flexible diet with variable carbohydrate intake, without detriment to glycemic control. However, large carbohydrate meals may contribute to poorer outcomes, through impact on late postprandial glycemia.