To determine the separate and combined effects of high-protein (HP) and high-fat (HF) meals, with the same carbohydrate content, on postprandial glycemia in children using intensive insulin therapy (IIT). Thirty-three subjects aged 8-17 years were given 4 test breakfasts with the same carbohydrate amount but varying protein and fat quantities: low fat (LF)/low protein (LP), LF/HP, HF/LP, and HF/HP. LF and HF meals contained 4 g and 35 g fat. LP and HP meals contained 5 g and 40 g protein. An individually standardized insulin dose was given for each meal. Postprandial glycemia was assessed by 5-h continuous glucose monitoring. Compared with the LF/LP meal, mean glucose excursions were greater from 180 min after the LF/HP meal (2.4 mmol/L 95% CI 1.1-3.7 vs. 0.5 mmol/L -0.8 to 1.8; P = 0.02) and from 210 min after the HF/LP meal (1.8 mmol/L 0.3-3.2 vs. -0.5 mmol/L -1.9 to 0.8; P = 0.01). The HF/HP meal resulted in higher glucose excursions from 180 min to 300 min (P < 0.04) compared with all other meals. There was a reduction in the risk of hypoglycemia after the HP meals (odds ratio 0.16 95% CI 0.06-0.41; P < 0.001). Meals high in protein or fat increase glucose excursions in youth using IIT from 3 h to 5 h postmeal. Protein and fat have an additive impact on the delayed postprandial glycemic rise. Protein had a protective effect on the development of hypoglycemia.