When a doctor diagnoses insulin-dependent diabetes, you will quickly learn that precise carbohydrate counting and correct insulin dosing for meals and higher blood sugars are both key to effective diabetes management.

But terms like “insulin to carbohydrate ratio” and “correction factor” can get confusing, especially if you’re newly diagnosed with the condition.

This article will explain how insulin works when eating food and how to dose insulin to keep blood sugars in range.

All humans need insulin to live. It helps digest the glucose (sugar) contained in most foods, particularly:

  • fruits
  • dairy
  • vegetables
  • grains
  • any food where sugar is added in processing

All carbs are processed into glucose that’s eventually converted into energy that fuels the brain and body.

As that sugar moves from the bloodstream into cells, it makes your blood sugar levels rise.

In people without diabetes, the body automatically adjusts for this cycle on a natural autopilot.

For people with diabetes, the insulin-producing cells in the pancreas don’t make insulin the same way they do in those without the condition. That means people with diabetes must address that insulin functionality for regulating glucose levels themselves.

People with type 2 diabetes (T2D) may not require insulin treatment because lifestyle changes can manage the condition.

That is not the case for type 1 diabetes (T1D). T1D is an autoimmune condition. People with T1D require insulin treatment by injection or with a diabetes device because their bodies don’t make it on their own.

Snapshot of different insulin brands

The particular type of insulin you take depends on many factors, including prices and insurance plan coverage.

Talk with your diabetes care team or endocrinologist about the best options for you, particularly if affordability or access are getting in the way of the life-sustaining insulin you need.

Several types of insulin exist, but they generally fall into three broad categories:

Long-acting insulin

This insulin is typically taken just once or twice per day. The dose doesn’t tend to change much day to day. This is known as “basal” insulin.

It works in the background throughout the day but doesn’t account for factors like food, exercise, stress, or other factors that impact glucose levels. Some common name brands include:

  • Lantus
  • Levemir
  • Basaglar
  • Semglee
  • Tresiba
  • Toujeo

Rapid-acting insulin

Some people with diabetes take rapid-acting insulin for most meals, snacks, and drinks. It works in the body more quickly and brings down blood sugars faster.

Rapid-acting insulin usually stays in the bloodstream for a few hours (depending on the brand and your body’s reaction to it); this is called a “bolus” of insulin.

The dose of rapid-acting insulin can vary greatly depending on how many carbs you’re consuming. Some main brands include:

  • Humalog
  • Novolog
  • Apidra
  • Fiasp

Human insulin

This is an older type of insulin that was first available in the 198s and before. The most commonly known brands include Humulin or Novolin R (Regular) and NPH insulin.

The pharma companies making this insulin are Novo Nordisk and Eli Lilly. Its brand names are Novolin or Humulin.

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People using insulin pumps rely solely on rapid-acting insulin for both their bolus insulin and basal insulin. The insulin pump releases a very small amount of insulin in constant increments throughout the day, mimicking a human pancreas.

People who don’t use an insulin pump may be injecting insulin multiple times a day. That might mean they take one or two long-acting insulin injections per day, whether that’s with a vial and syringe or a plastic prefilled insulin pen.

This is in addition to their rapid-acting insulin, which can also be taken in the form of a syringe and vial or with an insulin pen.

An insulin-to-carb (I:C) ratio is the amount of rapid-acting insulin required to essentially “cover” the number of carbs a person eats or drinks.

While many people tend to focus on calories when discussing food labels and nutritional information, those who live with diabetes and require insulin often look first at the carb counts on nutrition labels.

Everyone’s I:C ratio varies. This is because everyone’s diabetes is different. But as an example, an I:C ratio may look something like this:

Insulin-to-carb ratio formula

If your I:C ratio is 1:15, that means you take 1 unit of fast-acting insulin for every 15 grams of carb you’re eating or drinking.

So, if you eat and drink 45 grams of carbs for breakfast, you will then take 3 units of rapid-acting insulin for your meal.

This does not include any additional insulin (correction factor) that you would calculate to get a higher blood sugar into normal range. It also does not account for how different foods and drinks have differing effects on blood sugars and may require more complicated calculations.

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Always talk with your diabetes care team about what your goal blood sugar range should be. Those healthcare professionals can help you figure out your ideal I:C ratio based on many factors, including your:

  • age
  • sex
  • activity level and lifestyle
  • diet
  • sensitivity to insulin

Simply calculating your I:C ratio for a meal doesn’t take into account your insulin correction factor. This figure is how much 1 unit of rapid-acting acting insulin will lower your blood sugar.

For example, if you are dosing insulin for a particular carb amount, you’d want to take less insulin for those carbs if you’re having a blood sugar lower than 70 mg/dL.

You would also need additional insulin beyond the I:C ratio if you have a higher blood sugar at the time.

Correction factors are just like I:C ratios in that they can vary individually and even depending on the time of day. This is all part of the discussion with your diabetes care team to determine what might be the best rates for your needs.

To figure out a rough estimate of your I:C ratio, divide the number 500 by your total daily dose (TDD) of insulin, which includes both long-acting and rapid-acting insulin. This is known as the “500 rule.”

To roughly calculate your correction factor, take the number 1,800 and divide that by your TDD. This is known as the “1,800 rule.”

Remember, always work with your care team to finely tune both your I:C ratio and correction factor.

Most insulin pumps now do this math automatically when recommending a bolus of insulin. However, for people taking multiple daily injections, calculating these figures manually is required for all meals, snacks, and drinks.

Is there a typical insulin-to-carb ratio or correction factor?

Like all things diabetes, there is no typical or magic number.

However, a 1:15 insulin-to-carb ratio and 1:50 correction factor may be a good place to start before fine-tuning dosage and care.

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Both insulin-to-carbohydrate ratio and correction factor are important tools to have in your diabetes tool belt. They can help you better manage your diabetes and blood sugar levels so you feel better.

Insulin-to-carb ratio and correction factor can change over time. They depend on many elements, including lifestyle, diet, life circumstances, weight, sex, age, and health goals.

Always work with your doctor and care team to determine your most appropriate insulin-to-carb ratio and correction factor.