AimSecondary analyses were conducted from a randomized trial of an adaptive behavioural intervention to assess the relationship between protein intake (g and g/kg) consumed within 4 h before moderate‐to‐vigorous physical activity (MVPA) bouts and glycaemia during and following MVPA bouts among adolescents with type 1 diabetes (T1D).Materials and MethodsAdolescents (n = 112) with T1D, 14.5 (13.8, 15.7) years of age and 36.6% overweight/obese, provided measures of glycaemia using continuous glucose monitoring [percentage of time above range (>180 mg/dl), time in range (70‐180 mg/dl), time below range (TBR; <70 mg/dl)], self‐reported physical activity (previous day physical activity recalls), and 24 h dietary recall data at baseline and 6 months post‐intervention. Mixed effects regression models adjusted for design (randomization assignment, study site), demographic, clinical, anthropometric, dietary, physical activity and timing covariates estimated the association between pre‐exercise protein intake on percentage of time above range, time in range and TBR during and following MVPA.ResultsPre‐exercise protein intakes of 10‐19.9 g and >20 g were associated with an absolute reduction of −4.41% (p = .04) and −4.83% (p = .02) TBR during physical activity compared with those who did not consume protein before MVPA. Similarly, relative protein intakes of 0.125‐0.249 g/kg and ≥0.25 g/kg were associated with −5.38% (p = .01) and −4.32% (p = .03) absolute reductions in TBR during physical activity. We did not observe a significant association between protein intake and measures of glycaemia following bouts of MVPA.ConclusionsAmong adolescents with T1D, a dose of ≥10 g or ≥0.125 g/kg of protein within 4 h before MVPA may promote reduced time in hypoglycaemia during, but not following, physical activity.