Is Carbohydrate Counting the Optimal Approach for Determining the Insulin Dosage for a Patient With Newly Diagnosed Diabetes?

Q: What is carbohydrate counting?

A: Carbohydrate counting helps manage blood glucose levels in patients with diabetes mellitus. This dietary tool has been used since the 1920s when Dr Elliott Joslin taught it to his patients. Carbohydrate counting is effective for both patients with type 1 diabetes and those with type 2 diabetes.

There are two types of carbohydrate counting: basic and advanced. The goal of basic carbohydrate counting is to eat a set number of carbohydrates with each meal. When the amount of carbohydrates eaten is kept stable, and the patient is on a consistent medication regimen, there will be less variability in blood glucose levels. Advanced carbohydrate counting uses an insulin-to-carbohydrate ratio to determine the exact amount of insulin necessary for a given meal or snack. Advanced carbohydrate counting allows for more flexibility in eating and insulin administration as well as potentially better glucose control.

Q: Why does carbohydrate counting make sense?

A: Although insulin therapy is the cornerstone of diabetes management, a dietary strategy is necessary for proper insulin dosing. Carbohydrate is the primary nutrient affecting postprandial glucose levels. The more carbohydrate that is consumed at one time, the higher the blood glucose level will rise. Therefore, if the amount of carbohydrate in a meal is known, a person can administer the exact amount of insulin necessary to cover the meal. By doing this, elevated postprandial glucose values can be avoided, leading to better glucose control and improved quality of life.

Q: Who can benefit from carbohydrate counting?

A: Carbohydrate counting is essential for persons with diabetes who hope to improve their glucose control. For patients who inject insulin, an accurate carbohydrate count can allow for more accurate dosing of pre-meal fast-acting insulin such as aspart, lispro, or glulisine. More accurate dosing can decrease both glucose variability and the chance of harmful hyperglycemia or hypoglycemia. Carbohydrate counting is also important for those who use oral diabetic medications or manage their diabetes with diet and exercise. An accurate carbohydrate count makes it easier to eat consistently from one day to the next and determine if additional treatment is necessary.

Q: What are the difficulties of carbohydrate counting?

A: There are many potential barriers to carbohydrate counting. Many patients report that counting carbohydrates is too time-consuming and are unwilling to put in the effort. Others report difficulty in understanding the strategy and the necessity for it. 

To many patients, a “lifetime of calculations” seems unnatural and frustrating. Studies have shown that, when given a choice, patients are more likely to discontinue carbohydrate counting compared with other strategies.¹ 

Physicians rarely have the time to teach carbohydrate counting during appointments; therefore, it must be taught by dieticians or other appropriately trained health care providers. Unfortunately, in some practices a lack of diabetic support staff can make this impossible. However, while counting carbohydrates can require dedication and time in the beginning, it often becomes easier with experience. It has been noted that, either for convenience or preference, most people eat the same 75 foods.² Once carbohydrate counts have been determined for these foods, there is no need to recalculate them. As the patient becomes more experienced with carbohydrate counting, these calculations become second nature. Therefore, for those patients who stick with it, the resultant improvement in glucose control is well worth the initial effort.

Q: What are the benefits of carbohydrate counting?

A: Carbohydrate counting allows for increased flexibility with meal choices, missed meals, and changes in appetite. It may also serve as a “cue-motivator” by encouraging patients with diabetes to pay closer attention to dietary choices and better adhere to sensible weight-management strategies. Overall, it can enhance quality of life, simplify meal planning, and allow for better glycemic control.

Q: What is an insulin-to-carbohydrate ratio and how is this calculated?

A: The insulin-to-carbohydrate ratio is the amount of carbohydrate covered by one unit of fast-acting insulin. For example, an insulin-to-carbohydrate ratio of 1:15 means it takes one unit of fast-acting insulin to cover 15 grams of carbohydrate. However, everyone responds differently to insulin. Therefore, one unit of insulin may cover 15 grams of carbohydrate in some adults, whereas it may only cover 5 grams of carbohydrates in others. A starting insulin-to-carbohydrate ratio is usually estimated for a patient using the 500 rule. Dividing 500 by the total daily dose of insulin can approximate the grams of carbohydrate covered by one unit of insulin. However, this is only a starting point; the carbohydrate ratio must be fine-tuned by analyzing pre-meal and post-meal blood glucose readings with known carbohydrate intakes.

Q: Does carbohydrate counting make a difference?

A: Yes. The effectiveness of carbohydrate counting has been well documented in the type 1 diabetes population. In children, precision with carbohydrate counting is associated with lower HbA_1c values and less glucose variability.^3,4 Furthermore, carbohydrate counting results in improved glycemic control in a short period of time with no weight increase despite a higher total daily insulin dose.

Carbohydrate counting is a useful adjunct to glycemic control in adults with type 2 diabetes. However, its necessity for good glycemic control has been less studied in this population. In our experience, carbohydrate counting remains the optimal approach to determining insulin dosage with each meal in this population. If patients are able and willing to eat the same amount of carbohydrate with each meal, a basic carbohydrate counting strategy can be used. For those more motivated patients, advanced carbohydrate counting is the optimal strategy for fine-tuning glycemic control.