Meal-planning is one of the cornerstones of diabetes management, and carbohydrate counting is one of the basics of diabetes meal planning. Keeping track of the amount of carbohydrate you eat is important because carbohydrate (rather than protein or fat) is the type of nutrient that affects blood glucose levels the most. Both eating moderate amounts of carbohydrate and spreading out the total amount of carbohydrate eaten over the day can help with blood glucose control. Carbohydrate counting additionally allows people who use short-acting or rapid-acting insulin before meals to fine-tune their premeal insulin doses based on the amount of carbohydrate they plan to eat.
There are several methods of counting carbohydrates, and one of the most precise is using carbohydrate factors to calculate the amount of carbohydrate in a portion of food. To use this method, the weight (in grams) of a portion of food is multiplied by the percentage of the weight of the food that is carbohydrate (and not protein, fat, water, or other substances).
For example, carbohydrate accounts for 15% of the weight of any apple. If a particular apple weighs 225 grams, the amount of carbohydrate in that apple can be calculated as follows: 225 grams X 0.15 = 34 grams of carbohydrate.
This method can be particularly useful when eating foods that vary in size, such as fresh fruit, or that are not easily measured by other means. For example, if the label on a package of potato chips lists the serving size as 15 chips but most of the chips in the bag are broken, it’s nearly impossible to know how many chip pieces make up 15 whole chips. But you can weigh even the smallest potato chip crumbs and multiply the weight by the carbohydrate factor for potato chips.
Even when a food can be measured easily in a measuring cup, weighing it and multiplying its weight by its carbohydrate factor can produce a more accurate carbohydrate count. For example, it’s easy enough to measure out a cup of cornflakes. But a cup from the top of a newly opened box, with mostly whole flakes, has a different amount of carbohydrate from a cup from bottom of the box, which has just a few whole flakes and a lot of crumbs. Weighing the cup of cornflakes shows you exactly what you have.
Finding carbohydrate factors
Before you can use the carbohydrate factor of a food to evaluate your portion, you must know what it is. Perhaps the easiest way to get the carbohydrate factor for a food is to take the information from the Nutrition Facts panel that is on the label of all packaged foods. The Nutrition Facts panel on a box of Rice Krispies, for example, says that one serving of the cereal is 1 1/4 cups, which weighs 33 grams (under laboratory conditions). The Total Carbohydrate line shows that one serving contains 29 grams of carbohydrate. To get the carbohydrate factor for this cereal, divide the weight per serving (33 grams) into the total carbohydrates per serving (29 grams) for a carbohydrate factor of about 0.88 (meaning that 88% of the weight of Rice Krispies is carbohydrate).
To use this information, put your cereal bowl on your gram scale and zero it out. Pour in whatever amount of cereal you want, and multiply the weight by the carbohydrate factor (0.88). Then, while the bowl of cereal is still sitting on the gram scale, zero out the scale and pour in the milk. Use the carbohydrate factor for milk (0.05) to figure how many grams of carbohydrate you’ve added to the cereal. If you want some banana slices in your cereal, zero out the scale again and slice in as much banana as you want. Multiply the weight of the banana slices by the carbohydrate factor for bananas (0.23), and add that to your running total. Result? One bowl of cereal with the exact amount of carbohydrate known — and only one bowl and one spoon to wash.
For another example of calculating carbohydrate factors from a food’s Nutrition Facts panel, see “Carbohydrate Factors at a Glance.” For other resources for finding carbohydrate factors, see “Where to Find Carbohydrate Factors.” Our “Carbohydrate Factor Reference List” shows the carbohydrate factors for several foods.