Adjusting Insulin For Dietary Fat  

It may be time to start counting fat in addition to carbs to lower A1c effectively, and adjusting insulin for dietary fat consumption. 

Despite counting carbohydrates properly, many patients still have issues with glycemic control, especially after meals that are high in fat. Research has shown that dietary fat impacts glucose levels after meals. The American Diabetes Association recommends incorporating fat and protein into mealtime insulin dosing, but optimal insulin dose adjustments are still unclear. 

This study sought to determine the effect that dietary fat had on postprandial glucose in adults with type 1 diabetes, and to determine proper insulin dose adjustments to achieve postprandial glucose control in meals with varying fat content. This study was a randomized, within-subject trial that compared blood glucose after meals as well as insulin requirements after meals with different amounts and types of dietary fat. Participants had to be between 18 and 65; to have had type 1 diabetes for at least a year; to have used insulin pump therapy for a minimum of 6 months; with an HbA1c of ≤8.5%; and performed four or more blood glucose checks a day. Some of the reasons that patients were excluded were celiac disease, gastroparesis, or eating disorders. Patients were given a random, prepared test meal. They were required to complete an overnight fast, and their blood glucose was tested 30, 15, and 0 minutes before the test meal. After the test meal, their blood glucose was checked using a glucometer at 0 minutes, 15 minutes, 30 minutes, 45 minutes, 1 hour, and then every 30 minutes until 5 hours had passed. The test meals had equal amounts of carbohydrates (45g) and varying amounts of dietary fat (0, 20, 40, or 60g), and three types of fat – monounsaturated, polyunsaturated, or saturated fat. In arm 1, insulin doses for each patient were given based on their calculated insulin/carbohydrate ratio and administered 15 minutes before the meal. This was given as a 50/50% split over 2 hours to reduce the risk of hypoglycemia. In arm 2, insulin doses and duration were estimated using a model predicted bolus that was also given as a split over 2 hours. The primary outcome was the incremental area under the curve for blood glucose for 5 hours after the meal.  

In the 16 participants, there were no significant differences seen in the 5-hour incremental area under the curve for glucose based on the type of fat consumed, nor were there any statistically significant differences observed for any of the blood glucose metrics. Interestingly, increasing the amount of fat did not significantly change the overall 5-hour incremental area under the curve of glucose. The amount of fat did, however, significantly alter the dose-response when comparing early (0-2 hours) and late (2-5 hours) responses, with higher amounts of fat lowering the early glucose response (P < 0.001) and increasing the late glucose response (P = 0.001). Consuming both fat and carbohydrates significantly reduced the lowest blood glucose levels (P = 0.018) and caused the lowest level to occur earlier (P = 0.009). While the peak blood glucose did not significantly change, the time to peak was increased dramatically with increasing amounts of fat (P < 0.001). The study found that the incidence of hypoglycemia was significantly decreased with increasing numbers of fat in meals. Two instances of hypoglycemia were observed with the meals containing 20g of fat, both of which were mild and were seen towards the end of monitoring.  

This study found that the type of fat consumed has no significant impact on postprandial blood glucose. Instead, it is the amount of fat that impacts blood glucose. It found that insulin delivery should be adjusted based on the amount of fat consumed and that the dose may need to be modified to minimize the risk of hypoglycemia. The suggestions are as follows: 75/25% split over 1.25 hours for a meal with 20g fat, 65/35% split for a meal with 40g fat, and 50/50% split over 1.75 hours for a meal with 60g fat. It suggests that insulin be increased by about 20% for a meal with 60g of fat that also includes carbohydrates. These were appropriate for most of the participants, though the authors suggest personalizing the doses based on each patient. Further research is needed to find the impact that varying amounts of protein have on blood glucose and insulin requirements.  

Practice Pearls: 

• Increased amounts of fat in meals resulted in a later glucose peak when compared to lower fat meals. 
• With increasing amounts of fat in a meal, the researchers suggest splitting prandial insulin: 

• • 75/25% split over 1.25 hours for a meal with 20g fat 
  • 65/35% split over 1.25 hours for a meal with 40g fat 
  • 50/50% split over 1.75 hours for a meal with 60g fat. 

• It was suggested that insulin be increased 20% in meals with 60g fat that included carbohydrates. 

References for “Adjusting Insulin For Dietary Fat”:
American Diabetes Association. “9. Pharmacologic Approaches to Glycemic  Treatment:Standards of Medical Care in Diabetes-2019.” Diabetes Care, American Diabetes  Association, 1 Jan. 2019, care.diabetesjournals.org/content/42/Supplement_1/S90 

Kirstine J., et al. “Amount and Type of Dietary Fat, Postprandial Glycemia, and Insulin  Requirements in Type 1 Diabetes: A Randomized Within-Subject Trial.” Diabetes Care,  American Diabetes Association, 1 Jan. 2020, care.diabetesjournals.org/content/43/1/59. 

George McConnell, PharmD. Candidate, LECOM School of Pharmacy 

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