Timing your insulin for meals

When it comes to managing Type-1 Diabetes, insulin is without any doubt the biggest tool in our arsenal. With a wide varieties of insulin out there like Novorapid, Humalog, etc. it can be confusing to corroborate whether the insulin we’re on is suited to our lifestyle or not. Let’s go over the classification of insulin types first before we see how can we use them more efficiently to manage T1D.

1. Ultra-rapid acting: They start acting within 10 mins of injecting and are usually advised to taken just before one starts their meal

2. Rapid acting: They take around 15–20 mins after injecting to start lowering your levels

3. Short acting: Their onset can be anywhere between half an hour to an hour and they last longer in your bloodstream as compared to rapid acting insulins

4. Intermediate acting: The onset time can vary between 1–2 hours post injecting and has a very gradual lowering effect

5. Long acting: These can last from anywhere between 18 to more than 24 hours depending on the variant. Most of these have a very flat action profile i.e. their peak is very minimal and hence works well as a basal or ‘background’ insulin.

The chart below analyzes the different types of insulin based on their onset, peak and duration of action:

To have a graphical look at the action profile consider the graph below:

Notice the sharp peak for the pink-colored ultra/rapid acting insulin, the gradual peaks for the Regular and NPH insulins and the almost flat action profiles for the long acting insulins.

But why do we need to know this?

This is a question some of you might be wondering about. To put it simply, knowing the action profile of your insulin can help you time your meal and dosing better to avoid those mountain peaks on your CGM monitor.

Carb counting helps in deciding how much bolus you would be needing for you meal but does carb counting all by itself help you avoid those peaks in your levels? NO!

Consider you’re having a glass of juice for which you know the carb content accurately and hence are able to estimate the bolus requirement. There’s still a high chance that your levels will peak out-of-range and then fall back soon after. While it’s not all bad as long as it does fall back in range soon, would it not make you happier if your levels would have been in range throughout without making you think (even if for a short while) “why is it shooting up?” or “when will it come down?”

So before we answer on how to effectively tackle this peak, we’ll need to introduce two terms: Glycemic Index (GI) and Glycemic Load (GL)

The Glycemic Index (GI) is a measure of the blood glucose-raising potential of the carbohydrate content of a food compared to a reference food (generally pure glucose)

Carbohydrate-containing foods can be classified as high (≥70), moderate (56–69), or low GI (≤55) relative to pure glucose (GI=100). Consumption of high-GI foods causes a sharp increase in postprandial blood glucose concentration that declines rapidly, whereas consumption of low-GI foods results in a lower blood glucose concentration that declines gradually.

The Glycemic Load (GL) is obtained by multiplying the quality of carbohydrate in a given food (GI) by the amount of carbohydrate in a serving of that food.

In simple words, GI is defined for individual food items whereas GL is defined for meals (usually comprising multiple food items). For example, if we add protein to our carbohydrate rich meal, it brings down the GL of the meal whereas the GI of individual food items remain unaffected.

Below is a graphical look of the two extremes of food GI:

Most of the items we eat will have the GI graph in between the two extremes shown above.

Now coming to our previous question:

“How can we reduce the meal spikes to better manage our type-1 diabetes?”

The answer is simple: We just need to sync the peak of our meal’s GL with the peak of our bolus insulin’s action profile!

So consider the same scenario where we are bolusing for juice. We know the carb content already and hence are able to estimate our bolus dose accurately. The GI of juice is on the higher side and hence will peak in 15–20 minutes (refer to the GI graph above). Now if our bolus insulin is say Fiasp, we know it’ll peak in 30–60 mins. So a good way to match their peaks would be to bolus around 15 minutes before our juice so that once the juice’s action of raising our blood sugar levels is peaking after 15–20 mins, it’d have been around 30 minutes since our Fiasp dose and it’s activity of lowering your blood sugar will be at it’s peak too, thus avoiding huge blood sugar variations.

This might seem like too many factors to consider at once but once you start playing around with timing your dose differently for different kinds of meals, you start getting a hang of it and before you know it, it would already have started making a big impact on your diabetes management! :)