Short answer: Carb counting means adding up the grams of carbohydrate in what you eat. MedlinePlus says people who take insulin can use it to work out the insulin dose they need at meals, and that a dietitian or diabetes educator teaches the method. The insulin labels give no formula: they say the dose is set for each person and may need to change with meal patterns. In trials, structured training helped A1C in adults with type 1 diabetes.
MedlinePlus explains that the body quickly turns carbohydrates into glucose, which raises blood sugar. Carbs are in fruit and juice, bread, cereal, pasta and rice, milk, beans, starchy vegetables such as potatoes and corn, sweets and snack foods. Most green, non-starchy vegetables are very low in carbs, and meat, fish and eggs have none.
In carb counting, one serving (sometimes called one carb) is the amount of food with 15 grams of carbohydrate. MedlinePlus says to use the total carbohydrate number on a food label, which already includes sugar and fiber, and to measure cooked foods after cooking. Some of its examples of about 15 grams:
| Food | Amount |
|---|---|
| Cooked long grain rice | 1/3 cup |
| Bread | One 1 oz slice |
| Milk or soy milk | 1 cup |
| Melon or berries | 1 cup |
| Cooked oatmeal | 1/2 cup |
| Popcorn (popped) | 3 cups |
MedlinePlus says people with diabetes who take insulin "can use carb counting to help them determine the exact dose of insulin they need at meals," and that a dietitian or diabetes educator teaches the technique. It suggests seeing a dietitian about every 6 months to refresh the skill.
The insulin labels leave the numbers to the care team. The Humalog label (section 2.3) says to individualize the dose based on a person's metabolic needs, blood glucose results and glycemic goal, and that dose changes may be needed with changes in physical activity, meal patterns (what is eaten or when), kidney or liver function, or during illness. Section 5.3 lists changes in meal pattern, including the mix of carbs, fat and protein, among things that can raise the risk of low blood sugar.
So the label does not give a carbs-to-units formula. How many units go with a given number of grams is set by the prescriber or educator for each person.
A 2014 review and meta-analysis (Bell 2014) pooled seven randomized trials of carb counting in type 1 diabetes, with 599 adults and 104 children. Across all trials, A1C was 0.35 percentage points lower with carb counting, which was not statistically significant. In the five trials in adults with a parallel design, A1C was 0.64 points lower. The authors called this some evidence for carb counting in adults.
The DAFNE trial (2002) taught 169 adults with type 1 diabetes to match insulin to what they chose to eat. At 6 months, A1C averaged 8.4% in those trained first and 9.4% in those still waiting. Severe lows, weight and blood fats did not change, and quality of life improved.
MedlinePlus suggests a log book, a sheet of paper or an app while learning, and says estimating gets easier with time. Dose Track logs each insulin dose with the time and a note, so meals, doses and readings sit on one timeline to review with your care team. Timing matters too: see how long before a meal to inject mealtime insulin.
Read more on Dose Track: HbA1c · Hypoglycemia (low blood sugar) · Blood sugar · Log a dose in Dose Track