Rethink Optimal Insulin Dose Calculations

Type 1 diabetes patients need to pay attention to the amount of fat as well as carbohydrates in their diet when calculating insulin doses, according to a new study.

“This study demonstrates that insulin dose calculations need to consider meal composition in addition to carbohydrate content and provides the foundation for new insulin-dosing algorithms to cover meals of varying macronutrient composition,” stated the researchers, led by senior author Howard A. Wolpert, MD, of the Joslin Diabetes Center in Boston, MA.

The results suggest a shift in the way insulin doses should be calculated for individual meals. Previously, studies have shown that both fat and protein can cause postprandial hyperglycemia, but not much is known about adjusting insulin to account for the amount of fat or protein in a meal.

Studies show that dietary fat and free fatty acids (FFAs) can impair insulin sensitivity and enhance hepatic glucose production. Lowering FFA levels in nondiabetics and type 2 diabetics can lead to both improved insulin sensitivity and glucose tolerance. Researchers have given considerable interest to the role of dietary fat and circulating FFAs in the pathogenesis of type 2 diabetes, but relatively little attention has been paid to the possible implications of FFA-induced insulin resistance for the treatment of type 1 diabetes.

“Restriction of dietary fat intake is an important nutritional consideration in individuals striving for tight glycemic control. Carbohydrate counting is a foundation for calculating meal-time insulin doses. However, to achieve optimal glycemic control carbohydrate counting needs to be combined with specific focus directed at identifying whether higher fat (or high glycemic index) meals are contributing to glycemic fluctuations, in conjunction with individualized guidance about changing to alternative meal/food choices with less glycemic impact. Some form of meal-planning should be an explicit focus of nutrition counseling in patients with type 1 diabetes,” said Wolpert.

The researchers set out to examine the differences in postprandial glycemia over a six-hour period after 10 adults with type 1 diabetes consumed low-fat, low-protein and high-fat, high-protein meals with identical carbohydrate content, covered with identical insulin doses. Later, the participants repeated the high-fat, high-protein meal with an adaptive model-predictive insulin bolus until target postprandial glycemic control was achieved. All patients were on an insulin pump.

With the same insulin dose, the high-fat, high-protein meal increased the glucose incremental area under the curve more than two-fold (13,320 vs. 27,092). To achieve target glucose control following the high-fat, high-protein meal, 65% more insulin was required with a 30%/70% split over 2.4 hours. The additional amount varied widely among study participants, ranging from 17% to 124%.

Most of the fat-related increase in glucose occurred 80 minutes after the meal, they noted.

The effect of fat on a patient’s insulin requirement varies widely. Therefore, the requirements for insulin dosing need to be individualized, they stated.

Protein has less of an impact on post-meal glucose. Insulin dose adjustment may be required with meals that contain at least 75 grams of protein.

The researchers published their results online in Diabetes Care.

Reference: Bell KJ, et al. Optimized mealtime insulin dosing for fat and protein in type 1 diabetes: application of a model-based approach to derive insulin doses for open-loop diabetes management. Diabetes Care. July 7, 2016.