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Eating with Diabetes: Counting ''Net'' Carbs

What Are Net Carbs? How Do They Affect Blood Sugar?

Since low carbohydrate diets became popular, the phrase "net carbs" has become a fairly regular fixture on the labels of food products. But, if you are not familiar with the term you may be wondering what in the world it means!

There are three types of carbohydrates: starches, sugars and fiber. All three types of carbs are added up and listed as Total Carbohydrates on the Nutrition Facts Label of a food product.

The concept of net carbs is based on the fact that, although it is considered a carbohydrate, dietary fiber is not digested the same way the other two types of carbohydrates (starches and sugars) are. While starches and sugars are broken down into glucose (blood sugar), fiber isn't treated the same way. The fiber you eat passes through the body undigested and helps add bulk to your stool (among other benefits). The indigestibility of fiber is where the idea of "net carbs" comes in. In fact, sometimes, net carbs are sometimes referred to as "digestible carbs.''

In recent years, food manufacturers have started including net carbs in addition to total carbs when labeling products. Many foods proudly display net carbs on their labels to entice both low-carb diet fans and people with diabetes.

While the concept of net carbs can be utilized in diabetes meal planning, read labels with a discerning eye. At present there are no mandated rules for calculating or labeling net carbs on food packages. The FDA does not regulate or oversee the use of these terms, and exactly what is listed as "net carbs" can vary dramatically from product to product. Some products calculate net carbs as total carbohydrates minus dietary fiber, other labels reflect net carbs as total carbohydrates minus dietary fiber minus sugar alcohols, and still others calculate net carbs as total carbohydrates, minus dietary fiber minus sugar alcohols minus grams of protein.

Many packaged foods that are marketed as high in fiber low in carbs actually add extra fiber, such as inulin, polydextrose and maltodextrin, to food products to lower the net carb serving. Most nutrition experts agree that these "stealth fibers " do not have the same health benefits and may not have the same benign affect on blood sugar levels as foods that contain naturally occurring fiber. As you can see, the whole issue of "net carbs" can get tricky very fast. And for people with diabetes, for whom carbohydrate counting and blood glucose control is a serious issue, referring to net carbs on a food label can have serious consequences.

However, counting net carbs can work for people with diabetes who use a meal-planning technique known as carbohydrate counting to help balance their blood sugar levels—when done correctly.

Here's how a person with diabetes can count net carbs safely and effectively:
  • The food in question must contain at least 5 grams of dietary fiber in the serving size you are planning to eat.
  • Read the Nutrition Facts label or look up the nutrition facts of the food to find both the total carbohydrates and total fiber for the serving size you plan to eat.
  • Subtract HALF the total grams of fiber from the total grams of carbohydrates to calculate the net carbs in your food serving.
  • Always perform this calculation yourself and do not rely on "net carb" totals listed on any food label.
Take the following example (see food label, left):

This product has 5 grams of dietary fiber, which means you can subtract half that amount (2.5 grams) from the total carbohydrate (23 grams) to calculate net carbs, which equals 20.5 grams per serving.

The whole point of counting net carbs versus total carbs is to allow someone to eat more of a carbohydrate-containing food without adversely affecting their blood sugar levels. If you find the issue of net carbs confusing, don't worry about it. There is no reason to use this technique if counting total carbohydrates works well for you. Both options can work as long as you are doing them correctly and reading "net carb" labels with a discerning eye.

For more specific information or help, talk to your health care provider. The American Diabetes Association's National Call Center also offers live advice from 8:30 a.m. to 8 p.m. EST, Monday through Friday at 1-800-DIABETES or 1-800-342-2383.

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Member Comments

  • This is not a full understanding of net carbs as I understood it. If you are eating whole foods like say a cucumber, then all the fiber can be subtracted bc there are no additives or starches or anything else that would affect the carb count. I thought this method was only to be used for processed foods. Like if your going to eat some chips then this would be true or a better way to count carbs. Has anyone else had it explained to them like it was explained to me? Have I been doing it wrong?
  • Informative article, very helpful when making food choices.
  • Im keeping the carbs down!
  • Trying to get my net carbs down... so good article.
  • I am never sure about amount of carbs I should have
    I need to keep reviewing Carb Counting over and over to completely understand it.
    SO very helpful!
  • Never heard to subtract only half the fiber. I'm new to low carbs and have been subtracting my total fiber grams from the total carb grams in the nutrition tracker. It seems to be working for me. Although, I am not diabetic and I eat mostly whole foods.
    Thanks for this. I had never heard of "net carbs" before!
    Yes, the "Low Carb Craze" was perfect for the tweekers amongst us to foul up the rules to suit themselves ! Just count the carbs and forget the trying to get two more bites of food......
    And a POX on doctors handing out diet sheets instead of referrals to a real dietician, those are "no nothing, don't bother me" doctors, should not be allowed to practice anymore!
  • Sounds a bit like voodoo to me: eating more of the food because the fiber is reducing the carb count is raising the calorie count; one expert says subtract half, another says subtract it all, the third says only make the subtraction when the fibre count is more than 7; stay within the range and all will be good. 8-)
  • Good article, When diagnosed with Type II diabetes I asked my Dr. about carb counting, he just handed me an info sheet which was very confusing, then I was told by a friend that it was meant to go with a diabetic exchange meal plan not provided.

    Anyway, now I'm convinced that I just need to count actual Carbohydrates instead of trying to play this loosely defined net carb game.

    And why can't I get a straight answer when I say, I'm this age, height, weight, and sex, How many carbs should I have per meal or per day?
  • Excellent article!
  • that was an eye opener. never realized the tricks they play with net carbs. why do you subtract only half the fiber grams?
  • For the last 6 months I have concentrated my efforts on watching carbs. Basically, not going over 35-45 carbs..per meal (usually 30 or so) I am a type 2 and its imperative for me to reduce my weight and get in far i have taken off approx 35-40#. I am excited to look and feel better.

About The Author

Amy L. Poetker Amy L. Poetker
Amy Poetker is a licensed and registered dietitian and certified diabetes educator with a master's degree in dietetics. Amy, who has spent most of her career working in diabetes education, is dedicated to the treatment of that disease and the prevention of related complications. See all of Amy's articles.