Remember the protein: calculating meal-time insulin dosing in type 1 diabetes

This study examined whether the meal-time insulin dose should be calculated based on the carbohydrate count or the combination of carbohydrate plus protein. The study concluded that calculating the dose based on both carbohydrate and protein may be more effective.

Patients with type 1 diabetes can benefit from a low-carbohydrate diet (defined as less than 100 g of carbohydrate a day). This diet can help reduce weight, reduce insulin requirements, and improve blood sugar. Because of this, many patients may replace carbohydrates with higher amounts of protein. The protein and fat in meals can also affect blood sugar after meals. It is thought that if protein is considered when performing mealtime insulin injections, it might mean that the blood sugar stays in a tighter range.

This study included 16 patients with good knowledge of carbohydrate counting. For the four weeks before the test, they ate less than 100 g of carbohydrate per day. After a ten hour overnight fast, patients were given a protein shake, which had 14g of carbohydrates, 2g of fat, and 40g of protein. They then either injected insulin based on their own carbohydrate counting ratios, or they injected based on their own carbohydrate counting ratios PLUS additional insulin to account for the protein. Blood sugar levels were tested over three hours after the meal. Each patient completed six sessions. In  three sessions they only counted carbohydrates, and in the other three they counted both carbohydrates and protein.

When protein was accounted for, an average of 2.6 extra units of insulin were given. The average blood sugar over the next three hours was 8.6 mmol/L when the carbohydrates and protein were counted, and 10.0 mmol/L when only carbohydrates were counted. The amount of time in which patients had blood sugars over 8 mmol/L was 54.8% when the protein was counted, and 73.7% when the protein was not counted. There was no issue seen with low blood sugars when the additional dose was given.

This study concluded that counting the protein in a meal as well as the carbohydrates resulted in a lower average blood glucose and spending more time below 8.0 mmol/L after a meal.

Protein takes a longer time than carbohydrates to have an effect on blood glucose, which needs to be taken into account when calculating insulin dose. As this study was quite small, larger studies would be needed to make sure there are no issues with low blood sugars.

It is important to discuss any changes in diet or in insulin calculations with you doctor beforehand.