You will also need a reliable source of nutrient information, such as one of the printed or electronic listings mentioned earlier, to know how much carbohydrate is in a standard portion. The list in “Carbohydrate Per Cup” gives approximate carbohydrate counts for one cup of some common foods. Using this information, you can calculate that the 1 1/4-cup portion of cantaloupe pictured in “Estimating Portion Sizes,” at 20 g per cup, has about 25 grams of carbohydrate (20 x 1 1/4). Three large handfuls of popcorn would have 5 g/cup x 3 cups, or 15 g carbohydrate. Half a “baseball” of peas has 30 g/cup x 1/2 cup, or 15 g carbohydrate.
This approach allows you to closely estimate the carbohydrate count of a food item if no other means are available. Again, it is best to practice this method with some packaged food items (where a label is available) to hone your skills.
The “type A” way
If you’re looking for a more scientific, precise (albeit somewhat less practical) method of carbohydrate counting, carbohydrate factors are for you. This technique involves weighing a portion of food on a scale and then multiplying the weight of the food (in grams) by its carbohydrate factor (which represents the percentage of the food’s weight that is carbohydrate). Doing so will produce a fairly precise carbohydrate count for that portion of food.
For example, apples have a carbohydrate factor of 0.13, which means that 13% of an average apple’s weight is carbohydrate. If an apple weighs 120 grams, the carbohydrate count is 120 x 0.13, or 15.6 grams.
As is the case with portion size estimation, carbohydrate factors should only take into account the food portion that will actually be consumed. Peels, rind, skin, seeds, or packaging should be removed before weighing. The apple measurement, for instance, may slightly overestimate the carbohydrate count since the apple core is not usually eaten.
Here are carbohydrate factors for some common foods:
- Apple: 0.13
- Apple pie: 0.32
- Bagel: 0.51
- Baked potato: 0.22
- Carrot (raw): 0.06
- Cheese pizza: 0.32
- Ice cream (chocolate): 0.27
- Spaghetti (cooked): 0.26
Condensed lists of carbohydrate factors can be found in my book (The Ultimate Guide to Accurate Carbohydrate Counting) and in the book Pumping Insulin, by John Walsh and Ruth Roberts.
You can also find the carbohydrate factor of any food listed in the USDA’s National Nutrient Database for Standard Reference by looking up the carbohydrate content in 100 grams of the food item, then using that number as the percentage of carbohydrate by weight. For example, 100 grams of Cheerios contains 74.68 grams of carbohydrate. That means that Cheerios are about 75% carbohydrate. If your portion weighs 30 grams, you would multiply 30 x 0.75 to get 22.5 grams of carbohydrate.
Registered Dietitians (RDs) who are also Certified Diabetes Educators (CDEs) take great pride in helping people with diabetes learn to count carbohydrates. To find a diabetes and nutrition expert near you, call the American Dietetic Association Nutrition Hotline at (800) 366-1655, or the American Association of Diabetes Educators referral service, 800-TEAM-UP-4 (832-6874).