Impact of Fat, Protein, and Glycemic Index on Postprandial Glucose Control in Type 1 Diabetes: Implications for Intensive Diabetes Management in the Continuous Glucose Monitoring Era

Access: Bell et al (2015) Impact of Fat, Protein, and Glycemic Index on Postprandial Glucose Control in Type 1Diabetes: Implications for Intensive Diabetes Management in the Continuous Glucose Monitoring Era. Diabetes Care 2015;38:1008–1015.

Who is the lead author or research group?

This paper was co-authored by the lead researchers from the Universities and Hospitals with the most effective and influential research programs for type 1 diabetes and nutrition.

The University of Sydney, Australia. This group previously pioneered work on the Glycaemic Index and Food Insulin Index.

The University of Newcastle, Australia. This group is pioneering research into different bolus methodologies for fat and protein.

The Joslin Diabetes Centre, Boston. Leading Diabetes Centre in the US.

Harvard Medical School. Leading international nutritional science centre.

This combination of authors and centres turns this paper into THE MUST READ in this area.

Type of Research:

Systematic Review of all pertinent research papers between 1995-2014 in the main electronic search databases: PubMed, MEDLINE, Embase, Cochrane Library.

Rigour of The Research

Pros

Originally 156 studies were identified but only 29 studies passed the strict eligibility criteria. This level of scrutiny gives this papers recommendation extra credibility.

Cons

It is not surprising a lot of the papers did not make the cut, because the quality of nutrition-related trials is often poor.

Reviewer Code

PG – Phil Graham

JP – John Pemberton

Key Findings

Fat: Seven studies passed the eligibility criteria.
- As fat intake increases, so does blood glucose level.
  - JP: It’s time to accept that it’s not just carbohydrate that impacts on blood glucose level.
  - PG: Dietary fat has the ability to impact blood glucose levels. While it may not influence blood glucose as quickly as carbs or protein, it is important to know the fat content of your meal when dosing.

Fat reduces the rise in blood glucose level in the first 2-3 hours due to delayed gastric emptying.
- JP: If all insulin is given up front for high-fat meals there may be an increased risk of hypoglycaemia.
- PG: Dietary fat can slow down the release of glucose from the gut when a meal containing carbohydrates and fat is consumed. This needs to be accounted for when dosing bolus.

Fat increases the blood glucose level after three hours significantly.
- JP: More insulin is needed after three hours for high-fat meals, therefore split bolus (MDI) or dual wave (Pump therapy) is needed to prevent late hyperglycaemia.
- PG: It is equally important to monitor blood glucose levels before meals and 3 hours after. More insulin may be needed to account for meals higher in dietary fat.

Addition of 35g fat to a meal can increase glucose level by 2.3mmol/l (40mg/dl).
- JP: A fat intake of 35g is more than would be consumed for a “standard healthy meal”. Therefore, it is unlikely that fat needs to be considered for usual meals.
- PG: Unless you are eating carb/fat rich foods like pizza, fries or chocolate, you most likely don’t need to account for dietary fat.

Addition of 50g fat can increase the insulin requirement of a meal by two-fold.
- JP: For meals that contain high fat (35 grams or more), extra insulin will be needed. The insulin dose may even need to be doubled if fat intake hits 50g. NOTE, this is easily achieved when consuming a heavily cheesed pizza, an indulgent three-course meal.
- PG: You definitely need to consider administering more insulin for carb/fat rich foods like pizza, fries or chocolate with a fat intake above 35g.

Protein: Seven studies passed the eligibility criteria.
- As protein intake increases, so does blood glucose level.
  - JP: It’s time to accept that it’s not just carbohydrate that impacts on blood glucose level.
  - PG: Protein has the capacity to increase blood glucose.

Protein intake starts to increase the blood glucose level after an hour and a half.
- JP: The additional insulin is needed earlier when compared to fat. Therefore, the additional insulin should before the meal rather than splitting the dose.
- PG: Protein has the potential to increase blood glucose levels faster than dietary fat alone. Therefore, insulin should be dosed sooner rather than later.

Protein consumed with carbohydrate requires more insulin than when protein is consumed alone.
- JP: A different calculation is required when determining the insulin dose for protein with carbohydrate compared to protein alone.
- PG: More insulin is needed for carb/protein based meals compared to protein-only meals.

Glycaemic index (GI): Seven studies passed the eligibility criteria.
- High GI foods (>70) spike blood glucose level.
- Low GI foods lower overall glucose response, reduce glucose peak and can increase the risk of hypoglycaemia.
  - JP: May need to reduce usual insulin dose for very low GI meals.
  - PG: Low GI meals impact blood glucose more slowly and can increase the risk of hypoglycaemia. Be mindful when dosing – less can be more in this case.

Total carbohydrate is more important than GI when determining insulin dose.
- JP: It is more important to get total carbohydrate count accurate first. Then try to reduce the GI of a meal with better quality choices.
- PG: Take time to calculate the total carbohydrate content of your meal, then look at ways and means to reduce the Glycaemic index. Adding fibrous green veg is a good start.

Different methods for giving extra insulin for fat, protein, and fat and protein together:
- Fat and Protein Unit (FPU) method: A complex calculation that equates the impact of 100kcal of fat and protein to equal the impact of 10g carbohydrate.
  - Both studies using the methodology showed a big increase in hypoglycaemia.
    - JP: The complexity of calculations and increase risk of hypoglycaemia means this method has very limited practical application.
    - PG: There is a high degree of hypoglycaemia risk when using the FPU method. Its reliability should be questioned.

Food Insulin Index method: A method that uses research on the insulin requirement of different foods, not just the glucose impact as the glycaemic index does. The method gives actual foods an insulin requirement ratio, not just the carbohydrate value.
- Two studies show improved glucose levels in the three hours after eating. However, the research data is limited to three hours after eating, and the impact of fat comes into play long after that.
- The food insulin index is currently limited to 147 foods, and for it to be used widely a larger variety of foods is needed.
  - JP: This system needs more work before it can be used widely in the type 1 diabetes population.
  - PG: More research is required before this method can be trusted and used in people living with type 1 diabetes.

Studies using insulin doing algorithms driven by Continuous Glucose Monitoring (CGM) data improve glucose levels after eating.
- The findings need translating into equations that can be applied to commercial CGM systems, and people not using CGM.
  - JP: Future insulin pumps and CGM systems are working towards closing the loop. It may be a number of years before they are available commercially. Also, this technology requires very accurate CGM and the fact the person wants to wear several devices
  - PG: The technological innovations in diabetes management are very exciting. More research is needed to perfect these technological systems in relation to the ever-changing dynamics of human lifestyle.

Using all the available data the authors produced a flow diagram for healthcare professionals on how to approach adjusting insulin doses for fat, protein and glycaemic index:

Reviewers insight into how the research can be applied to people with Diabetes.

This review for the first time clearly proves some crucial points that many people with Type 1 Diabetes know from their personal experiences:

It’s not just carbohydrate that impacts blood glucose. Fat and protein both impact, and therefore require insulin.

Carbohydrate counting works when “standard healthy meals” are consumed, where the fat and protein moderate and consistent. But when large fat or protein meals are eaten, more insulin is needed.

The insulin to carbohydrate ratio is actually a ratio for your usual meals and takes into account the insulin requirement for your usual fat and protein intake.

This paper is especially important for people with diabetes who are into building muscle and improving body composition. Why? It is now clear that protein intake needs to be about 2g/kg (1g/lb) to optimise muscle building, and preserve muscle tissue when dieting. Therefore protein portions are larger compared to the general population, and more insulin will be required.

In the Training Lab, there have been two courses specifically designed to convert this research into practical strategies. They are packed full of simple strategies you can apply to improve your diabetes control. The courses are:

These courses will help you decide on the best insulin dosing strategy for you, depending on your dietary intake. The courses are also full of tried and tested strategies to control after-meal high glucose levels.