This is an extract from information available as Module E4B/P3B in our Essential and Advanced courses for Healthcare Professionals.
This is a short practical session to provide an experience of the day-to-day issues of Type 1 management. The information applies to any dietary choice for Type 1. It is not specific to ketogenic diets. This practical module concerns bolus insulin calculations.
Insulin dosing for food.
Much of this course content concerns the impact of food on blood glucose. All three macronutrients impact blood glucose levels in the following order, carbohydrates, protein, and fat.
The most important metric for people with Type1 diabetes is the carbohydrate content of a meal.
Carbohydrate content is easily assessed. There are numerous nutrition calculators available for fresh foods. Most supermarket websites will have this information. There is also www.myfitnesspal.com which is a popular resource. The Carbs and Cals app is similarly useful. https://play.google.com/store/apps/details?id=com.chello.carbsandcals&hl=en_GB&gl=US. Also, Carb Counter markets itself as suitable for a keto diet https://apps.apple.com/gb/app/carb-counter-carbs-and-cals/id1482997900
Reading Food Labels
There will be a food label on the packet for any wrapped food. The carb content of other foods can be found in one of the apps above.
When assessing a food label, the first thing to do is ignore the front-of-pack label. (fopl) It is an industry initiative to provide a quick reference about the health of the food in the pack. However, it is based on the SACN (Scientific Advisory Committee on Nutrition) recommendations for high carbohydrate, low-fat diet. Often, manufacturers manipulate the portion size of the fopl to make the food seem healthier than it is. Sugars are on the front label but often bear no relation to carbohydrates on the rear label. In this example, there are 25g of total carbohydrates in a tiny 30g serving of this cereal. Few people in practice eat such a small amount. It might be a useful exercise to measure 30g of breakfast cereal.
The rear pack label is useful as it contains all the information required for people with Type 1 diabetes to make informed decisions about insulin management for any macronutrient.
The easiest thing to do is examine the number of carbohydrates per 100grams. As a very rough guide, any food with a carb content under 10g/100g will be okay, bearing in mind that carbs add up over a day. In this example, a tiny portion of this cereal would provide almost the whole day’s carbohydrates for a ketogenic diet.
Fructose-containing foods will not form part of a ketogenic diet apart from berry fruits. Sugar alcohols are unlikely to cause glycaemic control problems, so they can be ignored. However, a few people notice a glucose-raising effect, so this information should be conveyed for completeness.
The total amount of carbohydrates for food combinations should be counted for the meal, and the insulin estimation will be based on the ICR ( Insulin to Carbohydrate Ratio). Typically a starter of 1:10 is used for a rough approximation. The patient will refine this over time. Many people who have had Type 1 for roughly 10 years or more will have some insulin resistance, especially if they have been on a high carbohydrate low-fat diet. They may be in the habit of injecting roughly the same amount per meal. These people are unlikely to get swings in glucose control, but their glucose levels will tend to run high. Their insulin volume is not so critical (due to the insulin resistance,) but there is still a risk of hypoglycaemia. Once on a keto diet, they will likely notice that they regain some insulin sensitivity over time. Therefore, it is good practice to re-educate your patients to work out their ICR and count carbohydrates.
Work through these examples of common foods, not necessarily ketogenic foods, because initially, some patients need to re-learn carb counting before transitioning. Understanding a range of foods will give a better framework for carbohydrate values.
Calculating Bolus Insulin Volumes ( Fiasp, Novorapid, Humalog, etc)
Start by working out the bolus insulin dose for the carbohydrate content. Then do the same for the protein content, which is half of the ICR. For example, if ICR is 1:10, IPR will be 1:20. Then, add the two together to work out the volume of insulin estimated for the meal. Fat will not be included in these calculations. It might be necessary to allow for fat later, but it does not need to be part of the calculations at this stage in learning. Fat can cause a slightly raised glucose plateau in some people. As long as patients know of it, they can work with this effect once they are on to the refinement phase. This course is primarily about getting patients started safely.
Grams of carbohydrate per serving = <0.5
Grams of protein per serving =15
Units of insulin for carbs based on 1 unit insulin for 10g carbohydrate ICR (1:10) = 0
Units of insulin for protein based on 1:20 =0.75
Total units of bolus insulin for this food. 1 unit of rapid-acting insulin. Pumps will get more accurate dosing but for practical purposes, round up. Remember 1 unit of insulin reduces blood glucose by around 2-3mmol/l. Some people are more sensitive than others. Some insulin pens will give 0.5 unit doses if some people are particularly insulin sensitive. Count all foods that make up the meal in the same way. It gets easier with practice and familiarity.
The injection timing will be determined to a small extent by whether this is a carb-heavy or protein-heavy meal. Protein usually causes peak glucose after 2-3 hours, so injection during a meal might work. Carbs give a peak within an hour of a meal, so if a meal is carb-heavy, then inject before a meal. People with Type 1 diabetes for more than ten years will have a degree of insulin resistance, so they will be less sensitive to the injection timing. However, this might change over time as insulin sensitivity improves on a ketogenic diet.
Grams of carbohydrate per serving =45.1
Grams of protein per serving =9.1
Units of insulin for carbs based on 1 unit insulin for 10g carbohydrate ICR (1:10) = 4.5
Units of insulin for protein based on 1:20 =0.5
Total units of bolus insulin for this food. 5 units of rapid-acting insulin.
Because this is a carbohydrate-heavy meal injection likely to be more beneficial before a meal, the timing will depend on the patients’ experience.
Grams of carbohydrate per serving of 2 slices =39.4g.
Grams of protein per serving =9.4g.
Units of insulin for carbs based on 1 unit insulin for 10g carbohydrate ICR (1:10) = 4
Units of insulin for protein based on 1:20= 0.5
Total units of bolus insulin for this food. 4.5 units of rapid-acting insulin. Round up or down based on experience. Round down for safety. Round up if the patient is more insulin resistant.
If this is to form part of a sandwich, the insulin dose must account for the spread and filling. Note that the sugar content and carbohydrate content are likely to be different. Always choose carbohydrate content.
Total grams of Carbohydrates per portion, including milk = 24 g
Total grams of Protein Per portion, including milk = 8.9 g
Volume of bolus insulin based on 1:10 ICR= 2.5 units
Volume of bolus insulin based on 1:20 IPR= 0.5 units
Estimated bolus insulin for this meal = 3 Units
It will be necessary to allow for full-fat milk, but in practice, there will be little difference.
Total grams of Carbohydrates per 2 squares (20g)= 3 g (2.8)
Total grams of Protein Per 2 squares (20g) = 2 g
Volume of bolus insulin based on 1:10 ICR= 0.3 units
Volume of bolus insulin based on 1:20 IPR= 0.1units
Estimated bolus insulin for this meal = 0.4 Units
It is not possible with 1-unit pens to accommodate such small volumes. Individuals will learn what to do from experience. Half-unit pens are available for insulin sensitive people.
Total grams of Carbohydrates per 100g= 3g
Total grams of Protein Per 100g = 3.6g
Volume of bolus insulin based on 1:10 ICR= units 0.3
Volume of bolus insulin based on 1:20 IPR= units 0
Estimated bolus insulin for this meal = 0 Units. Sometimes sugars get realised on boiling as cellulose breaks down.
Total grams of Carbohydrates per 100g= 6.2 g
Total grams of Protein Per 100g) = 0.4 g
Volume of bolus insulin based on 1:10 ICR= 0.6 units
Volume of bolus insulin based on 1:20 IPR= 0 units
Estimated bolus insulin for this meal = 0.5-1 Units. Glucose gets released on boiling as cellulose fibre breaks down.
Total grams of Carbohydrates per 60g( no one eats 30g!) = 50 g
Total grams of Protein Per 60g = 3.8g
Volume of bolus insulin based on 1:10 ICR= units 5
Volume of bolus insulin based on 1:20 IPR= units 0.2
Estimated bolus insulin for this meal = 5.2 Units. (5 in practice).
Total grams of Carbohydrates per 25g= 2.2g
Total grams of Protein Per 25g = 6.8 g
Volume of bolus insulin based on 1:10 ICR= 0.2 units
Volume of bolus insulin based on 1:20 IPR= 0.34 units (0.5 for practical purposes)
Estimated bolus insulin for this meal = 0.5 Units. Some might use a unit as nuts can easily be overconsumed.
Chicken Chow Mein
Total grams of Carbohydrates per pack= 47.8 g
Total grams of Protein Per pack = 34.9 g
Volume of bolus insulin based on 1:10 ICR= 5 units
Volume of bolus insulin based on 1:20 IPR= 1.5 units
Estimated bolus insulin for this meal = 6-7 Units
Total grams of Carbohydrates per apple= 16g
Total grams of Protein per apple = 0.5 g
Volume of bolus insulin based on 1:10 ICR= 2 units
Volume of bolus insulin based on 1:20 IPR= 0 units
Estimated bolus insulin for one apple = 2 Units. Some apples can be very large and sweet and so contain more carbohydrates than one would think.
Total grams of Carbohydrates per bar= 23 g
Total grams of Protein per bar= 4 g
Volume of bolus insulin based on 1:10 ICR= 2.3 units
Volume of bolus insulin based on 1:20 IPR= 0.2 units
Estimated bolus insulin for this snack = 2-3 Units.
Clearly, with 23g carbs and 19g sugar per bar, this is not suitable for people with Type 1 or Type 2 diabetes whether or not on a keto diet, but it is just used for illustration purposes.
With practice, people become adept at carbohydrate estimating. For food combinations and meals, simply estimate the macronutrients and use the calculated bolus insulin to suit. It should be clear now that smaller amounts of carbohydrates will require smaller volumes of insulin.