Clinical Application of the Effects of Fat, Protein, and Glycemic Index on Postprandial Glucose Control

Mealtime insulin dosing calculation should focus on meal composition—including fat, protein, and glycemic index—rather than carbohydrate counting alone, according to a systematic review published in the June issue of Diabetes Care.

Nutritional label

“Current guidelines only focus on carbohydrates as the basis for calculating insulin doses; however, data indicates that other micronutrients—namely fat and protein—can affect insulin requirements, and the other issues depend on the type of carbohydrates ingested,” explained senior author Howard A. Wolpert, MD, Associate Professor of Medicine, Harvard Medical School, and Director of the Joslin Institute for Technology Translation, both in Boston, Mass.

Beyond Carbohydrate Counting
“In clinical practice, patients need to be aware that these factors [fat, protein, and glycemic index] can impact on blood glucose levels,” said Dr. Wolpert. This concept is included in the American Diabetes Association’s 2015 Standards of Medical Care in Diabetes, which states, “For selected individuals who have mastered carbohydrate counting, education on the impact of protein and fat on glycemic excursions can be incorporated into diabetes management.”1

“And when it comes to review patients’ glucose logs, one needs to assess whether fat or protein are factors causing glucose fluctuations, and if they are, [health care practitioners] need to give patients guidance and counseling on identifying problem foods and making better food choices,” Dr. Wolpert said. There has to be a broader recognition that carbohydrate counting alone is too simplistic and monolithic, he said.

Incorporating Fat, Protein, and Glycemic Index into Insulin Dosing
The researchers identified a total of 21 studies on the effects of dietary fat (n=7), protein (n=7), and glycemic index (n=7) on acute postprandial glucose control in type 1 diabetes, all of which showed that these factors modify postprandial glycemia. They developed an algorithm for mealtime insulin dosing that includes the following elements:

  • Fat
    • For meals ≥40g fat, consider increasing total insulin dose starting with 30% to 35% increment using combo bolus with 50:50 split over 2 to 2.5 hours.
    • Review early postprandial glucose level and add more insulin upfront if levels are increased early postprandial.
    • Review late postprandial glucose levels and adjust total insulin dose as needed.
    • For patients taking insulin injections, consider giving an additional insulin dose (equivalent to 30% to 35% of the preprandial dose) 1 hour after mealtime or consider preprandial injection of regular +/- analog insulin.
  • Protein
    • Insulin may not need to be adjusted for protein-only meals <75 g protein.
    • For meals with ≥40 g protein and ≥30 g carbohydrates, consider increasing the total insulin dose by 15% to 20%.
  • High glycemic index
    • Consider administering insulin >20 minutes prior to meal or, if using an insulin pump, give an additional insulin dose upfront.
    • Consider alternative lower glycemic index meal choices.

Experiential Dosing
“What it really comes down to in practice is for patients to learn from experience how to dose insulin appropriately. In fact, most patients who have had type 1 diabetes for a long time and who are doing well have actually learned from experience how much insulin they need to dose for different meals,” Dr. Wolpert said.

Calculating Bolus Doses is Challenging for Patients
“The systematic review by Bell et al is a useful contribution to our knowledge of prandial insulin requirements in the context of continuous subcutaneous insulin delivery,” commented Fergus Cameron, MD, MBBS, DipRACOG, FRACP, Professor in the Department of Endocrinology and Diabetes and Centre for Hormone Research, Royal Children's Hospital and Murdoch Childrens Research Institute, and Department of Paediatrics, University of Melbourne, Victoria, Australia.

“It must be said though that the carbohydrate content of a meal is the dominant determinant of prandial insulin requirements and that many patients struggle to accurately (within 10-15 g) calculate carbohydrate content (as their research group has shown in other research)2 or, in the case of younger patients, to remember to bolus for meals at all,” Dr. Cameron said. “Interestingly though, their group also has previously shown that carbohydrate counting does not need to be all that accurate (+/- 10 g) to obtain good prandial insulin cover,” Dr. Cameron said.3

“The issue of use of glycaemic index in an ambulant setting was demonstrated to be effective in non-pump settings many years ago,” Dr. Cameron said.4 “Conceptually then, in a real-world setting, it is difficult to understand that given that the predominant requirement for prandial insulin is to cover carbohydrates and if a) people routinely only calculate this to within 10-15 g and b) this imprecise calculation doesn’t seem to matter, why would calculation of fat and protein (minor contributions to post prandial blood glucose levels) be important? This is difficult question to resolve in the context of the trial data reviewed. It begs the question as to whether the benefits seen are due to the fat and protein content affecting the glycaemic index of a whole mixed meal or the gluconeogenic potential of the fat and protein per se,” Dr. Cameron said.

“Having said this though, additional calculations of protein and fat content is in the realm of ‘advanced pumping’ for highly competent pump-users. Meal contents vary both within and between days. Pump-users need simple, intuitive and easily adaptable instructions as to how to calculate bolus requirements,” Dr. Cameron concluded. He added that translation of the algorithm for insulin dosing by Bell et al into a practical tool that can easily be used by patients is challenging.

Commentary by Amy Hess-Fischl MS, RD, LDN, BC-ADM, CDE
As a diabetes educator for over 17 years working with type 1 diabetes, it has been clearly evident that carbohydrate alone is not the only factor that affects postprandial blood glucose control. With the increased use of continuous glucose monitors, it has truly helped assess how to better adjust insulin doses to match when the foods are digesting.

It is easy to say that we should eliminate these foods to reduce the effect on blood glucose control, but we all know that quality of life plays a crucial role in managing this condition, and people with diabetes want to consume pizza and other higher fat foods occasionally. Our job is to help individualize their treatment plans to match their needs.

July 20, 2015




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