What Is Insulin to Carb Ratio?

You may have run across this term “insulin to carb ratio” and have wondered, what can that possibly mean for me? Is this some type of mathematics that my body is doing? Am I supposed to be calculating a math problem? Is there a hidden formula? And, if I’m supposed to use insulin to carb ratio (ICR or I:C), what should the ratio be?

Mealtime insulin to carb ration

Well, you’ve come to the right place for the answers. Insulin to carb ratio isn’t used by all people with diabetes. You may be asked to use this mathematical equation of ICR only if you are injecting “mealtime” insulin as part of your medication regimen for diabetes management. If you do not take “mealtime” insulin, you will not use an insulin to carb ratio.

A breakfast example

If you do take “mealtime” insulin, your doctor or your certified diabetes care and education specialist will help you set your insulin to carb ratio (I:C). As an example, let’s say your doctor set your insulin to carb ratio at breakfast for 1:15. This means that you will inject 1 unit of insulin for every 15 grams of carbohydrate eaten. Sound confusing? No worries, I’ll explain further. This is how you would put the I:15 ratio into play.

If you are planning to eat ½ cup of oatmeal, a poached egg, and a cup of black coffee for breakfast, you would inject 1 unit of insulin since the total grams of carbohydrate for this meal was 15 grams from the oatmeal. If you plan on eating 1 cup of oatmeal, a scrambled egg, and a cup of black coffee, you will inject 2 units of insulin since the total of this breakfast meal is 30 grams carbohydrate.

Why is insulin to carb ratio used?

The insulin to carb ratio formula was designed to help with blood glucose management in fine-tuning the amount of insulin to inject based on the total grams of carbohydrate consumed. It is not a set rule but instead can vary depending on how much insulin you will inject per grams of carbohydrate consumed. The insulin to carb ratio isn’t just one set of numbers throughout the day. Often your I:C ratio will be different at different times of the day. My personal I:C ratios right now vary between 1:9 and 1:19.

Can your ratio change?

These numbers may also change over time simply because there are semi-permanent or temporary variables that change within our daily lives. For instance, if you are going through menopause or sprained an ankle and can’t participate in your regular physical activity or are experiencing a lot of stress or restless night sleeping. All of these instances can catch up with you making changes in your diabetes management which may include an adjustment in the ICR.

Making adjustments

Our blood sugar levels vary throughout the day and night, so this I:C ratio gives us an opportunity to help our body. It’s highly recommended to continue checking your blood sugar levels and note if there is a pattern of higher or lower readings. If you are seeing above or below target readings consistently in a pattern your educator or doctor may make tweaks to your insulin to carb ratio. It’s also notable that insulin pump systems and various apps will conveniently make the meal-time calculations for us once we have entered our I:C ratios for various times of day.