What on Earth is Pre-Bolusing?

(Everything in this article in my own experience and is not to be considered medical advice. Please, consult your diabetic team before making any adjustments to your care)

What is pre-bolusing?

Pre-bolusing is the act of doing insulin prior to meals in order to balance the insulin action time and the action time of carbohydrates, in view to reduce post-prandial meal spikes.

Simply: doing insulin a certain amount of time prior to meals, which allows to eliminate the post-meal spike.


Why even bother to pre-bolus?

- Massive reduction in your HbA1C, as you stay in range much more.

- A lower standard deviation of your blood sugars.

- Easier blood sugar control, due to no spikes, blood sugar is less likely to go into hypoglycaemic levels after.

- You will be able to correct after a meal (once you have figured out your pre-bolus time), as you will see your blood sugars rise if the amount of insulin was insufficient, which will no longer be due to a spike.

- Improved energy levels and mood, as you will not feel lethargic after meals, and then tired when the blood sugar starts to rapidly fall.


How to start pre-bolusing.

This section is the most important. It comes in several sections: testing the time, understanding the meal, fine tuning, understanding when to correct again. It is very important that you figure out the times for yourself, as they vary for every individual. You must-must-must be very cautious about the time you take between giving the insulin and starting to eat.


Testing the time

A CGM or a Flash Glucose Monitor would be most preferable in figuring out how much time you need to pre-bolus. However, it is possible with just a regular meter, if you are willing to test many times. You will need to keep a very detailed and accurate record of what your blood sugar is and what was the timing of all of your actions.

I would recommend to start with a pre-bolus time of about 10-15 minutes maximum, reason being that fast-acting insulin aspart starts working in 15 minutes.

It is preferable that you eat pretty simple, same meals when figuring out your timings for your meals. Choose foods that you eat often and learn to pre-bolus for them.

Here is how to figure out exactly how much time you need to pre-bolus, broken into simple steps. You need to record the time, blood glucose value and what type of food, how many carbs you eat for every step.

1. Measure your blood sugar 15 minutes before your meal. Inject your insulin at this point.

2. Measure your blood sugar right before you start eating.

3. Eat your meal.

4. Measure your BG 20 minutes after your meal. Do not inject more insulin at this point, even if very high. You need the data from the high.

5. Measure your BG 40 minutes after your meal. Do not inject either.

6. Measure your BG 60 minutes after your meal. Measure again in 1.5 h and 2 h.

7. Look at your recordings. What was your blood sugar behaviour?

a) Has your blood sugar gone up and then rapidly came down to the starting point?

The pre-bolus timing needs to be extended, the insulin dose should be correct.

b) Has it gone up and stayed?

The timing may be wrong (cannot tell), the amount of insulin is definitely insufficient.

c) Has the blood sugar gone up a little and then became hypoglycaemic?

Too much insulin, timing may be wrong too (cannot tell).

d) Has it not moved much?

That is the perfect timing and amount of insulin for that time of day and type of meal.

8. Make adjustments according to the data that you have found from your previous test.

9. Repeat until you are satisfied and there is no significant peak after your meal. That will be your ideal timing.


Understanding meal composition (carbs, fats, protein)


Different types of meals will affect your blood sugars in different ways.

Fast-acting carbohydrates will work much faster as will cause a faster rise in blood sugars, which means you may need extra time for pre-bolusing for those types of meals. For example, say you normally leave 20 minutes between the insulin injection (or delivery for pump), for these meals you may want to leave 25-30min. You will need to test the desired time out via the suggested method above.

High fat meals – usually 30g of fat or more- prolong digestion. If you inject the full dose before a meal as a pre-bolus, you will most likely drop to very low blood sugar levels, which will need to be treated with extra carbohydrates. However, 3 hours after the meal you will get an “unexpected” rise in your blood sugars, which will be hard to get down if missed.

Therefore, when doing your insulin for a fatty meal, try splitting the dose: do a half up front and the other half in 2 hours (so that the insulin has time to start working before the rise starts). This will allow a more spread-out coverage and will prevent you going low straight after the meal. For individuals on a pump there is an option of an extended bolus, which could be used instead of the second injection: you do ½ the dose upfront and put an extended bolus for the rest of the dose.

High-protein meals may have a similar effect on blood glucose to high fat meals, but normally to a lesser extent. It is down to the individual’s reaction to high protein, but I would not split the dose in two, and just do all upfront.

Please, remember that all is very individual and you must test to identify patterns in your own blood sugars before proceeding with any modifications to your pre-bolus times or the ways you use insulin in your management.

Other variables that can affect the timing and dose

There is a huge number of variables that may affect the need for pre-bolusing and the amount of time left between insulin and the meal. They include, but are by far not limited to the below:

· BG level prior to the injection for the meal.

· Activity level prior to meal.

· Activity level several hours or even the day before the meal.

· The time of day (it is likely you may need different pre-bolus times for different times of the day).

· Stress levels that day and time.

· The weather and temperature in your environment and outside.

· Hormones (adrenaline, cortisol, growth hormones, puberty).

· Some weird unexplainable stuff happening in the universe, that affects your blood sugars in an unknown manner (haha, that you cannot predict, though).

It is important to consider those factors when making a decision on how long to pre-bolus every time you do it. At first, it will be challenging, but you get used to it, and then it just starts coming automatically.

-Fine tuning – combining factors

Combining all the factors, the meal composition and the current glucose levels is not the easiest of things, but once you start doing it, you will understand how important it is for your wellbeing and mood. You will get accustomed to doing pre-boluses and considering the factors.

Practice makes perfect.

Do not be frustrated with yourself at any point.

Understanding when to correct again

With experience, you will understand how insulin works in your body and at some point, you will be able to tell a spike from a blood sugar rise from an insufficient insulin dose. That will be amazing for your management, as you will then know if you need to correct or if that is just a spike and you can just leave to come down to level.

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