To determine the glycaemic impact of increasing protein quantities when consumed with consistent amounts of carbohydrate in individuals with Type 1 diabetes on intensive insulin therapy.

Participants with Type 1 diabetes [aged 10–40 years, HbA_1c ≤ 64 mmol/mol (8%), BMI ≤ 91st percentile] received a 30‐g carbohydrate (negligible fat) test drink daily over 5 days in randomized order. Protein (whey isolate 0 g/kg carbohydrate, 0 g/kg lipid) was added in amounts of 0 (control), 12.5, 25, 50 and 75 g. A standardized dose of insulin was given for the carbohydrate. Postprandial glycaemia was assessed by 5 h of continuous glucose monitoring.

Data were collected from 27 participants (15 male). A dose–response relationship was found with increasing amount of protein. A significant negative relationship between protein dose and mean excursion was seen at the 30‐ and 60‐min time points (P = 0.007 and P = 0.002, respectively). No significant relationship was seen at the 90‐ and 120‐min time points. Thereafter, the dose–response relationship inverted, such that there was a significant positive relationship for each of the 150–300‐min time points (P < 0.004). Mean glycaemic excursions were significantly greater for all protein‐added test drinks from 150 to 300 min (P < 0.005) with the 75‐g protein load, resulting in a mean excursion that was 5 mmol/l higher when compared with the control test drink (P < 0.001).

Increasing protein quantity in a low‐fat meal containing consistent amounts of carbohydrate decreases glucose excursions in the early (0–60‐min) postprandial period and then increases in the later postprandial period in a dose‐dependent manner.