Carbohydrates Affect On Blood Sugar And Diabetes | Cornerstones4Care®

Carbohydrates and Blood Sugar

It can take time to figure out how different carbohydrates (carbs) affect an individual’s blood sugar. Many people who have had type 1 diabetes for a while, or have had a lot of experience at being a caregiver of someone with diabetes, are experts at carb counting. But if you're new to diabetes or just need a reminder, this section can help.

Carbohydrates, proteins, and fats are the main nutrients in food that give the body energy. Sugars and starchy foods are examples of carbohydrates. Carbohydrates include vegetables, fruits, beans, whole grain cereals, grains, pasta, breads, and milk. Carbs can raise blood sugar levels more than other nutrients. That’s why it’s important to be aware of the amount of carbohydrates a person with type 1 diabetes eats.

Naturally occurring sugars are found in certain foods and added sugars can also be introduced into other foods when they are processed, like the heavy syrup that is often packed with canned fruit. Foods containing these extrinsic or added sugars tend to contain fewer healthy nutrients than foods that contain intrinsic or natural sugars. Regardless of their source, foods containing simple carbohydrates, which are broken down faster than complex carbohydrates, will begin to raise blood sugar levels very soon after they are eaten.

Starches take longer to break down in the body. As a result, they cause the amount of sugar in the blood to rise more slowly. How fast these carbohydrates affect blood sugar is measured by a system called the Glycemic Index.

Foods containing large proportions of carbohydrates are:

  • Starches—bread, cereal, crackers, grains, rice, pasta
  • Starchy vegetables—potatoes, corn, peas, beans
  • Fruits and fruit juices
  • Milk and yogurt
  • Sugary foods—candy, regular soda, jelly
  • Sweets—cakes, cookies, pies, ice cream

Because carbs can raise blood sugar faster than other nutrients, it may seem to make sense to cut them completely out of one’s diet. However, everyone needs to eat some foods with carbs because they provide the body with energy, along with many vitamins and minerals.

Even sweets may be okay once in a while, but remember that they usually have a lot of calories, as well as carbohydrates and fat. And sweets contain little nutritional value.

Creating a personal meal plan can help people with type 1 diabetes to control their blood sugar, while keeping some favorite foods on the plate, too.

Carbohydrate (carb) counting and diabetes

Carb counting is a good way to better understand how food intake can affect diabetes. It can also help to control blood sugar.

To count carbohydrates, one needs to:

  • Know which foods contain carbohydrates
  • Find out how many carbohydrates are in those foods
  • Read food labels and use measuring tools, such as measuring cups, spoons, and a food scale
  • Understand how food, physical activity, and medicines can affect blood sugar levels

How to figure out the carb counts of favorite foods

When counting carbohydrates, knowing how to read Nutrition Facts labels can make it easier. Two important things to look for when using a food label to count carbohydrates are serving size and the total grams of carbohydrate. Don’t worry about counting sugar and fiber grams for this purpose. They are already included in the total carbohydrate number.

Always remember to check the serving size. Information on the label is based on the serving size. Keep in mind that packages often contain more than 1 serving. See how many grams of carbohydrates are in each serving. Then decide whether the food fits into your meal plan.

Here’s a brief carbohydrate chart adapted from the American Diabetes Association:


Serving sizes for some carbohydrate foods
(each has about 15 grams of carbs) 


1 small (4 ounces)


¼ large (1 ounce)


1 extra small (4 ounces)


1 slice (1 ounce) or 2 slices reduced calorie bread (1½ ounces)

cake (unfrosted)

2-inch square

cereal, unsweetened (ready-to-eat)

¾ cup

cereal, cooked

½ cup


2 small (2¼ inches across)


½ cup

crackers (saltines)


fruit, canned

½ cup

hamburger bun

½ bun (1 ounce)

ice cream (light)

½ cup

jam or jelly

1 tablespoon

milk, fat-free or reduced fat

1 cup

orange juice

½ cup

pasta or rice (cooked)

⅓ cup

green peas

½ cup

pinto beans or kidney beans (cooked)

½ cup

popcorn (popped)

3 cups

potato, mashed

½ cup

potato chips

¾ ounce (about 9 to 13)


¾ ounce


⅓ cup


1 tablespoon

sweet potato

½ cup

taco shells

2 (5 inches across)

tortilla, corn or flour

1 (6 inches across)


Discuss carbohydrates with the dietitian 

Dietitians are trained in helping people with diabetes find the right amount of carbohydrates for their meal plans. They can help split up the amount of carbs needed among meals and snacks to help manage blood sugar levels.

People with type 1 diabetes either need to take multiple daily insulin injections or need to infuse insulin from a pump. One of the benefits of taking several injections per day (or using a pump) is having more flexibility in insulin dosing and food choices. Blood sugar will need to be monitored closely, but it may be necessary to adjust the amounts of fast-acting insulin given before each meal in order to:

  • Cover the carbs in that meal
  • Lower a high blood sugar level
  • Plan for a rise in blood sugar caused by the next meal

Working with the diabetes care team is the best way to fine-tune food intake, insulin doses, and blood sugar control. Remember, skipping meals is a bad idea. It can lead to low blood sugar, especially for people who take insulin. It’s important to have snacks on hand when planned meals need to be delayed. But don't forget to count the carbs in the snacks!

Balancing carbohydrates with insulin

There are two common ways that people count carbohydrates. 

Matching your carbohydrate intake to match your insulin dose

To count carbohydrates this way, you need to limit the number of servings of carbohydrates you consume so that it matches your fixed insulin dose. Doing so can help improve blood sugar control.

Or, you can do it the other way around:

Changing insulin dose to match carbohydrate intake

Matching the amount of fast-acting, or mealtime, insulin you take before eating to the amount of carbohydrates you choose to eat at a meal is another way to count carbohydrates. 

Learn about 2 different fast-acting insulins.

All Carbs Are Not the Same!

Counting carbs is important, but you also need to watch how quickly, or slowly, certain foods with carbohydrates cause your blood sugar to spike. The measure of this is called the glycemic index (GI).

No Label? No Problem!

One of the fastest and easiest ways to get carbohydrate information on thousands of foods is to use our Meal Planning Tools. You'll find these and other useful type 1 diabetes support program resources online from the Cornerstones4Care® Diabetes Health Coach.