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How do carbs affect my blood sugars?

By Megrette Fletcher, M.Ed., R.D., C.D.E
bagels in bowl

Take a look at the chart in our last post: How does eating affect my blood sugars?  Note that carbohydrates raise blood sugars–but they help stabilize them too. That is because eating too many carbs in one meal and not enough at the next is usually the cause of blood sugar swings.

Here’s why: When you have diabetes, your pancreas may not be able to make enough insulin to process all the carbohydrates you eat at one time. When you eat a large amount of carbohydrates at one meal, your blood sugar will rise. If you don’t eat enough carbohydrate at the next meal, your blood sugar will fall, causing your blood sugar levels to swing. These blood sugar swings often feel draining, lowering your natural energy level. So how many carbs do you aim for? Ideally, your diet (whether you have diabetes or not) will have about 45-75 grams of carbs eaten three times a day. For a great overview of carbohydrates, read chapter 12 of Eat What You Love, Love What You Eat for Diabetes.

If you see that your blood sugars are often elevated before lunch, eating less carbohydrate at breakfast may help keep your blood sugar in the target range two hours later. Here’s are two examples of how you could experiment with the number of carbs at breakfast to see how that affects your blood sugar two hours later:

Example # 1:
1 1/2 cups cereal = 44 grams carbohydrates
1 cup skim or 1% milk = 12 grams
8 oz juice = 30 grams
Total = 86 grams of carbohydrates
Possible changes:
1 cup cereal = 30 grams carbohydrates
1 cup skim or 1% milk = 12 grams
4 oz juice = 15 grams
Total = 57 grams of carbohydrates
Example #2
Bakery muffin or bagel = 85 grams carbohydrates
Large coffee w/milk & sugar = 15 grams
Total = 100 grams of carbohydrates
Possible changes:
Low-carb bagel = 45 grams carbohydrates
Large coffee w/milk & sugar = 15 grams
Total = 60 grams of carbohydrates

In our next post, we’ll see how fiber affects your blood sugars.


About the author

Megrette Fletcher is a registered dietitian, certified diabetes educator, author, and co-founder of The Center for Mindful Eating. Megrette is the 2013-2014 president of The Center for Mindful Eating, a non-profit, organization to assist health professionals to explore the concepts of mindful eating. She has written articles for and has been quoted about mindful eating in Diabetes Self Management, Today’s Dietitian, Today’s Social Worker, Bariatric Times, Glamour, Family Circle, The Wall Street Journal, US News and World Report, Women’s Day, and Oxygen Magazine. Megrette currently works as a diabetes educator in Dover, New Hampshire.


  1. Wayne says:

    Very nice list of substitutions. So, am I to read that your carb recommendations are 45 -75g per meal @ 3 meals a day. I think that’s pretty good. I know if I am for less than 150g per day I lose weight.

  2. Thank you for your comment. From your post, you understand that carbohydrates have the greatest effect on your blood sugar. Shifting the focus from restriction (limiting) to awareness (learning) of how different types of carbohydrates change your blood sugar level would be a great next step.
    For example: How does fiber containing carbohydrates affect your blood sugar or your feelings of fullness? Foods with >3 grams per serving are considered a high fiber source. Examples of these high fiber, carbohydrate containing foods include: fruit, whole grains, some starchy vegetables such as corn. For more information please read the post on fiber.
    By focusing on awareness of total carbohydrates many people find their overall blood sugar better managed. Often when blood sugars are in target, there is often a shift in hunger and a decreased food cravings.
    Mindful Eating can help a person become more aware of these changes. Working with your existing knowledge of nutrition, you may notice that when you refocus your awareness from restricting, limiting and counting to a more open and curious view your relationship with food changes.
    Questions to ask yourself before you eat:
    Why am I eating? Are you really hungry or is there some other reason?
    When am I eating? Is there a pattern to your eating? When stressed, while watching TV or making dinner?
    What am I eating? Can you notice anything about your food choices or food cravings?
    How am I eating? Are you eating in a way that allows you to enjoy and taste your choice fully?
    How much am I eating? Are you mindlessly eating? Do you taste your food or is your focus simply to eat?
    Asking the questions and being open to the answer they give can expand your learning about why you are eating. This is important information that can help you better manage your blood sugars.
    Megrette Fletcher M.Ed., RD. CDE

  3. Andrea Byer says:

    Andrea Byer

    wow, awesome post.Really thank you!

  4. CoraLynn Varone says:

    i thought that there was a way to use carbs via fiber to actually determine the amount of carbs you are consuming. If so could your give me the break down.

  5. Dietary fiber is not digested by the human body. When a person eats foods that are high in fiber, greater than 5 grams per serving, it is possible subtract the total fiber from total carbohydrates. In Eat What You Love, Love What You Eat, with Diabetes including fiber to the diet is a wonderful strategy to increase nutrition, fullness and blunt blood sugar rise. However, eating foods that you don’t like because they have fiber is not likely to be a long term strategy. Eat What You Love, Love What You Eat with Diabetes brings the concept of mindful eating which we have defined as eating with Intention and Attention. Including loved foods into your diet, simply because you love them brings joy and pleasure back to the table.
    So, if you love high fiber foods such as crunchy whole grain crackers or hearty whole wheat bread you could choose to subtract the fiber of these foods (if 5 grams or more) from the total carbohydrates to help you understand the effect of these foods on blood glucose rise. However, it is important to include loved foods into your meal plan. For example, you may choose to have a 1/2 sandwich on a rustic whole grain roll, (2 grams fiber) and pair this with a 2 cups tossed salad (2-5 grams fiber) a cup of low fat milk, and two pieces of chocolate for dessert. This meal has 4-7 grams of fiber and approximately 50 grams of carbohydrates and it offers foods from a wide variety of food groups.
    Testing your blood sugar before and 2-hour after a meal can help you evaluate the meal. The key point is, all carbohydrates fit into your diabetes meal plans, including those that are sweets or contain sugar. Enjoy!

  6. […] Carbohydrates are important when you have diabetes because the carbs in the foods you eat and the beverages you drink affect your blood sugar levels. This table provides a list of some popular flavors of milk alternatives and their carbohydrate content. I developed this general reference list by taking the average of the carbohydrate content of three popular brands. […]

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