Adjusting Mealtime Insulin Doses

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 insulin-to-carb ratio. This ratio may be 1 to 15 (written as 1:15) for someone who is very sensitive to insulin. The ratio might only be 1:5 for someone who is less sensitive to insulin.

A ratio of 1:10 means that for every 10 grams of carbohydrate they eat, a person needs to inject 1 unit of rapid- or short-acting insulin. Your doctor 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 do this, 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 30 and 50 mg/dL.

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.


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