Flexible Insulin Therapy:
Mealtime (bolus) dose adjustment
In Flexible insulin therapy (FIT), each mealtime insulin dose has two components: A ‘food dose’ that covers the carbohydrate content of that meal, and a ‘correction dose’ that takes into account your pre-meal blood glucose level and any exercise that you plan to do after the meal.
That's what makes this type of insulin therapy flexible. It allows you to change the insulin dose to fit your lifestyle. Calculating a mealtime dose takes a little practice, but it is not that hard. In fact, some of the newer insulin pumps have a built-in calculator that does this for you. Let's look at the steps in detail.
Step 1 : Cover the Carbohydrates
In order to cover the total carbohydrate servings in a meal you need to know your carb-to-insulin ratio. This ratio may be 15 to 1 (written as 15:1) for someone who is very sensitive to insulin. The ratio might only be 5:1 for someone who is less sensitive to insulin. A ratio of 10:1 means that for every 10 grams of carbohydrate they eat, a person needs to inject 1 unit of rapid- or short-acting insulin. Your diabetes educator can help you find the carb-to-insulin ratio that is right for you.

Step 2: Add or Subtract a Correction Dose of Insulin based on your Blood Glucose Level
To complete this step, you must know your Insulin Sensitivity Factor (ISF). This is sometimes called a ‘correction factor’. Your insulin sensitivity factor is simply a measure of the impact that insulin has on your particular body. Put a bit more technically, it’s the amount by which your blood glucose is reduced by one unit of rapid, or short-acting insulin in a period of two to four hours.
Your doctor can tell you what your insulin sensitivity factor is. For most people with diabetes, it is typically between 1.5 and 3.0 mmol/L per unit of insulin.

To calculate a blood glucose correction dose:

  • Measure your pre-meal blood glucose.
  • Subtract your target blood glucose level from your current test result.
  • Divide the resulting number by your ISF.
  • The result is your correction dose of insulin.

Let’s see how this calculation applies to our two previous examples:

Example: Active Teen on an Insulin Pump
The teenager from our last example calculated his lunch bolus dose at 7 units of rapid-acting insulin. Let’s suppose that his ISF is 2 mmol/L per unit of insulin, and that his target pre-meal glucose is 6.0 mmol/L.

Our teenager’s pre-meal blood glucose test reveals a level of 4 mmol/L. He subtracts 6.0 (the target level) from 4.0 (the actual level). The result is -2.0. Because the number is negative, he must correct his bolus dose downward. To find out exactly how many units to reduce the dose, he divides 2 (the difference between the actual and target levels) by 2 (his ISF). The result of this equation is 1 unit. He adjusts his pump to deliver 6 units of insulin instead of the 7 units he had previously calculated.

Example: Adult Woman Using Syringes
This woman had calculated her breakfast bolus dose to be 5.0 units of short-acting insulin. To calculate her correction dose, we need to know that her ISF is 1.5 mmol/L. We also need to know that her pre-breakfast blood glucose tests at 12.0 mmol/L and that her target pre-meal level is 6.0 mmol/L.

The woman subtracts 6 (her target level) from 12 (her actual level), for a difference of 6 mmol/L. She divides 6 by 1.5 (her ISF), and the result is 4 . She adds these 4 units to the original 5 units she had calculated, for a total breakfast bolus dose of 9 insulin units.

Step 3: Adjust for exercise
Many people underestimate how much exercise can lower blood glucose. If you enjoy active sports or even a brisk walk after lunch, you might be at risk for developing hypoglycemia during the exercise, or for several hours afterward. If you plan to exercise at some point after eating, you must lower your bolus dose to compensate. For added safety, keep glucose tablets with you during and after the exercise period.

The table below shows how bolus dose adjustments should be made for certain levels of exercise and blood glucose. This table is just an example - your situation may vary. Ask your doctor which exercises are right for you, and what specific adjustments you should make to your bolus dose.

Examples of insulin adjustment for exercise

Duration and intensity of exercise

Blood glucose level before exercise

4-6 mmol/L

6-10 mmol/L

10-14 mmol/L

Long duration, moderate intensity. (Examples: 60 minutes or more of playing team sports, golfing, cycling or swimming.)

Retest your blood glucose level after each hour of activity. Eat glucose tablet(s) if necessary.

Reduce insulin by 1 unit for every hour of activity.

Reduce insulin by 1 unit for every hour of activity.

Reduce insulin by 1 unit.

Moderate duration, high intensity. (Examples: 30 to 60 min. of running, high-impact aerobics, or kickboxing.)

Reduce insulin by 2 units.

Reduce insulin by 1 unit.

No adjustment needed.
Moderate duration, moderate intensity. (Examples: 30 to 60 min. of fast walking, tennis, swimming or jogging.)

Reduce insulin by 1 unit.

No adjustment needed for a glucose level of 6-7 mmol/L

Reduce insulin by 1 unit for a glucose level of 7-10 mmol/L.

No adjustment needed.

Short duration, low intensity. (Examples: 30 min. of yoga, walking or leisurely bicycling.)

Reduce insulin by 1 unit.

No adjustment needed.

No adjustment needed.

Let’s see how exercise adjustment applies to one of our previous examples:

Example: Active Teen on an Insulin Pump
The teenager with the 6.9 unit lunch bolus has three hours of football practice after lunch. That’s considered long duration, moderate intensity exercise. Recall that his actual pre-meal blood glucose is 6.0 mmol/L. The table above shows that he should reduce his bolus insulin by 1 unit for each hour of exercise. That’s a reduction of three units. Instead of taking a 6.9-unit lunch bolus dose, he sets his pump to deliver 3.9 units of insulin.