Why we count carbohydrates in type 1 diabetes

Carbohydrates (also called carbohydrates) are one of the three energy sources in food, alongside protein and fat. The carbohydrate group includes sugars, starch and fiber. They are found mainly in cereals and cereal products, potatoes, fruit, milk, yogurt, pulses and sweet foods [1].

Digestion turns sugars and starch into glucose, which then passes into the blood. Fiber is the exception, because your body lacks the enzymes needed to break it down. It stays out of the dose calculation: if the label lists fiber outside the carbohydrate total, use that total as it stands; if fiber is included in the total, subtract it. When you count carbohydrates, you are in fact counting the part of what you eat that will later become pure glucose [2].

Yes, and the difference is large. Almost all the starch and all the sugars in a meal eventually become glucose available in the blood. Protein raises blood glucose only partly, slowly and mainly when the portion is larger [3].

Fat does not turn into glucose. It slows stomach emptying and reduces insulin sensitivity for a few hours. The result is a delayed rise in blood glucose. Carbohydrates are used to set the mealtime insulin dose. Fat and protein influence when blood glucose rises and can shape the way you deliver the meal bolus, for example through a dual-wave bolus, as the figure below shows [4].

In stage 3 type 1 diabetes, the beta cells no longer release the amount of insulin you need at a meal. You are the one who has to decide the insulin dose before every meal. Carbohydrate counting turns the amount of food at a meal into a number that you can use to calculate the insulin dose for that meal [5].

Every patient has an insulin-to-carbohydrate ratio, that is, the number of grams of carbohydrate covered by one unit of rapid-acting insulin. The ratio can be personalized, including by time of day. The insulin dose then follows the meal, instead of the meal having to fit a fixed dose. The practical benefit is the freedom to eat a varied diet at different times of day [6].

Carbohydrate counting is a tool, not a treatment in itself. It helps when four conditions are met:

• the insulin-to-carbohydrate ratio is correct;
• the carbohydrate estimate is close to the actual amount;
• the insulin dose is calculated correctly;
• the timing of the dose is right [7] [8].

The main benefit is predictability. You know what to expect after a meal, and you need fewer correction doses for blood glucose that is too high 2-3 hours later. However, routine carbohydrate counting cannot make up for a wrongly set basal insulin dose, an unsuitable insulin-to-carbohydrate ratio or missed insulin doses [9].

No. Counting means measuring, not restricting. There is no ideal percentage of carbohydrate for people with diabetes, and the right amount is decided for each person. Meals with a lot of carbohydrate are worth discussing in more detail with your doctor [10]. Carbohydrate counting was created to replace fixed menus and to allow a diet that varies in both quality and quantity.

Quality still matters, quite apart from quantity. Choose foods that are as minimally processed as possible and rich in fiber. Cutting the amount of carbohydrate in a meal remains a separate decision, one you make together with your doctor. Even if you reduce the portion at one meal, your carbohydrate total for the day can still be the right one for you, as long as you spread the same amount across several smaller meals [2].

Besides quantity, the speed at which blood glucose rises after eating different types of carbohydrate also matters. Quantity remains the most important factor: 50 g of carbohydrate raises blood glucose far more than 15 g, whatever the food [3].

The speed depends on the form of the food and on the composition of the rest of the meal. Sugary drinks and fruit juices raise blood glucose fastest, because they contain no fiber and leave the stomach quickly. Fiber, fat and protein in the same meal slow the rise in blood glucose produced by a given amount of carbohydrate [4] [11].

The glycemic index compares carbohydrate-containing foods according to the rise in blood glucose they produce for the same standard amount of carbohydrate. A low index means a slower rise and a lower peak, which is an advantage in type 1 diabetes [11].

In carbohydrate counting, the total amount is the main focus, and the glycemic index always remains secondary. It can help you choose between foods that otherwise seem similar and time your injection more precisely [12]. Glycemic index values are determined for foods eaten on their own. Bear in mind that the same food behaves differently within a mixed meal [4].

It depends on the treatment. Although this page belongs to the type 1 diabetes section, the question matters to a great many people, because most people with diabetes worldwide have type 2 diabetes [13] [14]. If you take insulin with meals, the logic is the same as in type 1 diabetes, so counting carbohydrates is very useful [15].

If your doctor has prescribed fixed insulin doses, consistency in what you eat matters more. You should then eat similar amounts from one day to the next, and often at set times too. When a dose adjusted to the meal is an option, it is usually preferable to a fixed-dose regimen. If you are on a fixed-dose regimen, do not change it on your own — talk to your doctor about whether it suits you. If you are not on insulin, carbohydrate counting matters less. A simple estimate of portion sizes is usually more than enough [5].

The principle of carbohydrate counting is learned quickly, in one or at most a few sessions. You learn which foods contain carbohydrate, how to read the nutrition label and how to move from grams to portions — for example, a 30 g slice of bread contains around 15 g of carbohydrate, and a medium potato around 30 g of carbohydrate. The rest is simply the time you devote to it in everyday life. In fact, most of the learning comes from daily practice [1].

Accuracy, however, takes months of practice, especially with meals cooked at home, where you can use a kitchen scale [16]. In time, you will manage when eating out too. This kind of education works better when it is spread over several months and continues with repeated support sessions. Estimates by eye improve quickly at first. In the long run, however, they become less and less accurate, because habit takes the place of weighing and small errors add up over time. Recalibrating means going back to the kitchen scale now and then, to compare your estimate with the measurement [17].

The best person to teach you carbohydrate counting is a dietitian experienced in diabetes. Learning to count carbohydrates is always part of the structured education programs run by specialist diabetes centers. In these centers, nurses, psychologists and specialist diabetes educators work alongside the doctor [5].

The doctor who prescribes your insulin also sets and adjusts your insulin-to-carbohydrate ratio, including by time of day. Apps, food databases and estimation from photographs are additional aids [18]. Individual and group sessions work equally well, including those held online (synchronous or asynchronous) [19].