This study characterized the dose effect of whey protein isolate (WPI) ingestion on glucagon secretion, glycemia, and the underlying mechanisms in adults with type 1 diabetes. Twelve insulin pump–treated adults with type 1 diabetes (mean ± SD age 47.3 ± 16.4 years; BMI 26.1 ± 3.8 kg/m2) and six adults without diabetes (age 36.2 ± 20.9 years; BMI 27.3 ± 5.8 kg/m2) received 1) control (water), 2) low-dose WPI (0.25 g/kg), or and 3) high-dose WPI (0.5 g/kg). Those with diabetes replaced subcutaneou