Share this Article

Advanced Carb Counting

Sixteen Tips and Tricks for Calculating Carbohydrate Content Accurately and Efficiently

Managing type 1 diabetes effectively absolutely relies on determining how many grams of carbs there are in the serving of food in front of you. But this process can be overwhelming and time-consuming. Here we share with you the tips and tricks of carb counting that have simplified our lives as D-parents, and made managing diabetes, well… more manageable!

1. Calculating carbs by weight is more reliable than by volume

It’s habit to whip out the measuring cups to figure out the volume of those Saturday-morning Cheerios, but you may get more accurate results by turning to your nutritional scale. Think about what happens when you fill a measuring cup with large or irregularly shaped items – such as dry cereal, or whole strawberries, or chunks of potato – the volume of food can vary each time you measure, depending on how big the pieces are and how the material settles. (The bigger the air spaces between the pieces of food, the less accurate your volume measure is.) The weight of a given sample of food, however, is not affected by how big the pieces are, how the material settles, nor whether there are pockets of air between the pieces. So weight is consistent, and thus is a more reliable measure for carb counting (if you have a nutritional scale with a food database OR you know the carb factor for a given food).

2. Carb Factoring is a handy way of determining the carb content of a food.

A Carb Factor is a number which describes what percentage of a given food is carbohydrate. For example, the carb factor of Kellogg’s Cornflakes is 0.83, which means that 83% of its weight comes from carbohydrates; the carb factor for fresh strawberries is 0.06 which means that carbohydrates make up 6% of its weight; the carb factor for our family’s recipe for pineapple fried rice is 0.16 so 16% of its weight is carbs.

Why is this handy to know? Well, calculating a carb factor once and then writing that number on the package (of cereal, or crackers, or yogurt…) saves you time. You simply weigh a portion of that food and multiply by the carb factor to determine the carb content. In addition, your child has the flexibility to eat any size portion of a given food while still accurately determining the carb content; she doesn’t have to eat exactly 1/20 of that banana bread, or servings of cereal in 1/4-cup increments – she can dish out whatever portion fits her appetite and calculate carbs from there. Also, carb factors allow you to “reverse engineer” meals, to determine how much of a given food is needed to make a certain goal number of carbs.

3. The Glycemic Index of a food has a significant impact on post-meal blood sugars.

While the carb content of a food determines how much it will raise blood sugar, the Glycemic Index (GI) of a food describes how quickly it will raise blood sugar. This is largely because a food’s GI describes how quickly (or slowly) that food will be digested. A food with a low GI value will be digested more slowly than a food with a high GI value; thus a low GI food (such as oatmeal) will raise blood sugar slowly, while a high GI food (such as Cheerios) will raise blood sugar quickly.

More information on GI values, how they affect blood glucose, and how to adjust insulin dosing and timing based on a food’s GI value:
An Introduction to the Glycemic Index
Glycemic Index Explained

4. When counting carbs, it’s important to think critically.

There are times when the carb count you calculate may seem too high or too low – trust your gut and do some more research before giving your child insulin based on this result. Double-check the carb count using a different method of carb calculation (see Introduction to Counting Carbs and Carb Factoring). If still in doubt, it’s wise to monitor your child’s blood sugar closely (for resulting highs or lows) for a few hours after eating, in case the carb count is off.

5. Measuring Corn on the Cob, Apples on the core and Watermelon on the rind on a nutritional scale may be misunderstood.

Depending on the brand and age of the scale, when you use it to calculate the carb content of a cob of corn, the weight of the cob is likely included in the calculation, even though it will not be eaten. That is to say, if you place a full cob on the scale and enter the Cob Corn function, the scale output may say that there are 40g of carbs in the sample, but this calculation assumes that the full weight of the food on the scale is corn kernels, when in fact about half of the weight is the cob. One solution to this problem is to calculate the total carbs, including the cob, using the scale’s “Cob Corn” food category. Then after your child has eaten the corn, repeat the process with just the cob (using the same food category, ex. “Cob Corn”), and then subtract the second result from the first. This results in a carb count for just the amount that was actually consumed. In effect, you are calculating carbs for the total weight of the cob + kernels, acting as if the cob was corn kernels; then you are subtracting out the cob amount, leaving you with just the carb content of the kernels consumed.

The same process applies to whole apples and watermelon with the rind – you may simply use the scale’s “Apple With Skin” category (or similar – different models of scales have different category labels) or the “Watermelon” category for the pre- and post- measures.

Tips from the Trenches

When our family eats corn on the cob, we follow the above process. But in order to calculate the meal insulin dose so our son receives insulin before he eats, we estimate the corn to contain 20g of carbs. Then, when the meal is done, we calculate the actual amount of corn consumed and give him more insulin or more carbs as needed.

6. When used to find the carb content of mixed dishes, the results from the database in a nutritional scale may be accurate… or not.

There is great variety in mixed recipes such as lasagna, cinnamon buns, or baked beans: some lasagna recipes are heavy on the noodles, some heavy on the ground beef; some baked bean recipes go for the sweet effect with lots of molasses or sugar, others go for the savoury effect, using less sugary ingredients. Some pizza slices have thick crusts. Some cinnamon buns have tons of icing.

When you access the “lasagna” function in your scale’s database (as opposed to using the scale to calculate the weight of the lasagna only, and then using a recipe-specific carb factor to calculate the carb content of a serving), the scale results are based on a reference “recipe” or composition, which may or may not match the carb content of the actual recipe used for the food your child is eating. So take the scale results with a grain of salt. Where a carb factor is not known and cannot be determined, the scale’s database for mixed dishes will at least get you into the ballpark in terms of accuracy, but is not likely to hit a home run.

Note that the results for individual foods, such as fruits and vegetables, do not present this problem. A strawberry is a strawberry is a strawberry; that’s not true for lasagna.

7. For dry foods that you eat cooked, such as pasta, rice, barley, and quinoa, carefully consider how the carb content is cited on the package.

Usually, the weight of the portion size on the package’s nutritional information panel refers to a dry (uncooked) weight. You cannot use this weight to determine a carb factor, as the dry weight will be different from the final cooked weight (which includes the water absorbed through boiling). If the package does not specify dry vs. cooked, you may choose to check your results against another method of carb calculation before using the result to dose insulin. For example, compare the result to one of your “rule of thumb” guidelines: if you know that a cup of cooked pasta contains about 30g of carbs, and your calculation from the package results in 80g of carbs per cup, then something is wrong; likely the portion size on the pasta box refers to the dry weight, not the cooked weight. If still in doubt, it’s wise to monitor your child’s blood sugar closely (for resulting highs or lows) for a few hours after eating, in case the carb count is off.

8. Visual estimation of carb content is a handy skill to develop.

With a little practice, you can get “close enough” to the actual carb content of a food item by using visual estimation techniques. This is particularly handy when you are away from home, away from your scales and measuring cups and books and apps.

This is a learned skill. You can hone your visual estimation skills by estimating a given portion, then measure the actual carb content, and compare the two results. Over time, the amount of error will drop; you will get better and better at visually estimating carb content. Also, apps like Figwee and Carbs & Cals can help with visual estimation.

approximately 15g of carbs

approximately 35g of carbs

(Photo credit: Figwee)

9. The serving weight cited in the nutritional information on food labels does not always correspond to the actual contents of a given package.

For example, in single serving packages (such as chips or snack crackers), the amount of product contained in the package can, within the law, vary by a small percentage. This percentage of error may be enough to affect blood sugar. Further, some companies concern themselves with making sure the package contains the stated amount of product at a minimum, but if there is extra product in the bag, they see that as a bonus for the consumer. This may mean that your child is not getting enough insulin for the amount of product she has eaten, resulting in post-snack highs. If you see out-of-target blood sugars often in relation to a certain packaged food, next time you may want to check the actual weight of the serving size (using a kitchen scale) to make sure the resulting carb count for the portion is correct.

10. Be wary of the stated carbs in products purchased at grocery store bakeries.

The carb info listed on the package may not be as precise as you need it to be for dosing insulin. Carb content may be stated based on a certain portion size, but this may not be consistent with the portion size contained in a given package. For example, once when buying cheese sticks, I noticed that some cheese sticks were about 8” long, while some were shorter, about 6” long (all were about the same width). However, the carb content on all packages was listed according to “1 cheese stick”. But which cheese stick? The 6-inch one or the 8-inch one? In addition, a bakery label may reflect an average carb content across several different types of cookies, for example. In this case, it’s impossible to determine if the chocolate chip cookies you hold in your hand are higher than, lower than or the same as the average carb content of all the cookies produced in that bakery. In all cases, it is wise to double check your carb calculation using an alternate method and monitor your child’s blood sugar for a few hours afterward.

11. White Bread, Buns, and Bagels have a Carb Factor of about 0.5.

When you have home-made white bread, or store-bought white buns with no carb information on them, or with carb info on the package that seems suspect (i.e., you think to yourself, “That seems like a lot of carbs for this one little slice of bread!”), you can double check carb content by using a carb factor of 0.5. To do this, weigh the slice, arriving at a weight in grams. Multiply this weight (in grams) by 0.5. For example, if a given slice of bread weighs 30g, it has about 15 grams of carbs in it. When you use this rule of thumb, it would be wise to monitor your child’s blood glucose closely following the meal to make sure you have not given too much or too little insulin.

12. Potatoes (baked, boiled, or roasted) have a carb factor of about 0.2.

In other words, 20% of the weight of the serving is attributable to carbs. For example, if you have 100g of mashed potatoes, you can estimate that there is about 20g of carbs in that serving. The exceptions to this “rule of thumb” are french fries and hashbrowns which have a carb factor of about 0.25.

13. “Lite” often also translates to “higher carb”.

In the salad dressing and other condiments, the fat contained in the regular, full-fat version doesn’t raise blood sugar. When they replace the fat with something else, the “something else” may be high-fructose corn syrup or some other carb-rich ingredient, which increases the carb content of the “lite” version over the regular. Whether you choose one version or the other depends on your goals for your family’s nutrition – that is, is it more important to you that your family eats low fat salad dressing, or low carb salad dressing? There’s no universal “right” answer, but with information, parents can make informed choices.

14. Adding pure cocoa to homemade pancake batter doesn’t add any carbs.

And chocolate pancakes are yummy!

15. Kids with diabetes CAN have pizza!

We just need to know how to deal with the carbs and fat that pizza contains.
Pizza is a tricky food to carb count, for a few reasons:

  • There is no standard crust thickness, yet the thickness of crust may greatly affect the carb count.
  • A pizza is rarely cut into 12 exactly-equal slices, so the carb content varies between slices of the same pizza.
  • The cheese and meat toppings are high in saturated fat, which slows down digestion and increases insulin resistance, often resulting in high blood glucose readings several hours later.

More information on dosing insulin for tricky foods:
Glycemic Index Explained
Reduce Post-Meal Spikes Caused by Fat and Protein
The Pizza Solution:
  • Using a carb factor (based on weight and accurate nutritional info) will yield the most accurate carb count possible for a given portion.
  • Using the extended bolus feature on a pump, or splitting/delaying the meal insulin dose if on injections, may help mediate the effects of a low glycemic and/or high fat meal.
  • You may find that your child also needs a correction dose of insulin 8-9 hrs later because of the insulin resistance caused by the saturated fat. Some pumpers have found success in avoiding the need for this correction dose by adding a temporary basal increase for several hours after pizza is eaten, to counteract insulin resistance. Consult your diabetes team and/or pump company for guidance on using temporary basal functions.

16. Carb counting is not an exact science – it’s largely trial and error.

But you can get closer and closer with practice. When in doubt, start with a reasonable estimate, and document what you did, as well as the resulting blood glucose. In this way, you can more easily see what works well for your individual child (and what doesn’t); you can more easily spot the trends.

The above information was reviewed for content accuracy by clinical staff of the Alberta Children’s Hospital Diabetes Clinic.

This material has been developed from sources that we believe are accurate, however, as the field of medicine (in particular as it applies to diabetes) is rapidly evolving, the information should not be relied upon, as it is designed for informational purposes only. It should not be used in place of medical advice, instruction and/or treatment. If you have specific questions, please consult your doctor or appropriate health care professional.

Share this Article