The calculation of mealtime insulin doses is primarily based on the carbohydrate content of the meal because carbohydrate has the largest effect on postprandial blood glucose levels among the macronutrients. However, the fat and protein content of the meal can also influence postprandial blood glucose levels. In people with T1D, increasing the protein and/or fat content of a carbohydrate-containing meal increases postprandial blood glucose levels 2–5 hours after consumption[1] in a seemingly dose-dependent manner,[2][3] which necessitates additional insulin. It’s unclear how much more insulin is needed to optimize blood glucose control following a mixed meal containing large amounts of fat and protein, as it significantly varies between individuals.[1][4]
In studies that compared a low-carbohydrate diet (50–100 grams of carbohydrate per day) to a high-carbohydrate diet (205–245 grams of carbohydrate per day), total daily insulin dose was lower with the low-carbohydrate diet.[5][6][7]