IMPORTANT: Always discuss with your healthcare team everything directly linked to treatment of the disease. Below are not to be seen as medical advisories, only as basic knowledge that you can discuss with your team for individual recommendations. Please also remember that the idea of carb counting is highly theoretic/mathematic, but since the body is complex and diabetes as well, carb counting is no guarantee. Everything affects the glucose.
Carb counting is a method of estimating needed amount of insulin for a certain amount of carb intake (1). Everything affects the glucose but particular carbs needs insulin to be metabolized and used as energy. There are a few methods to estimate needed amount of insulin, and a correction dose to lower a high glucose value.
500 RULE
Divide 500 with your TDD, Total Daily Dose (total amount of insulin you take one day, including both bolus and basal). The result is an estimate how much carbs is covered by 1U (unit) insulin.
Example: Someone has a TDD of 50U insulin. 500/50 = 10. That means 10 grams of carbs covered by each unit of insulin. Theoretically.
350 RULE
Many are affected by hormones in the mornings, and that can also cause a temporary insulin resistance. This might affect the insulin needs, and therefore another rule can be used for breakfast. 350 rule is similar to the 500 rule but the purpose is to cover the extra insulin needs in the mornings.
Example: Someone has a TDD of 50U insulin. 350/50 = 7. That means 7 grams of carbs covered by each unit of insulin. Again, theoretically.
700 RULE
As the methods above but this is for situations when you have an improved insulin sensitivity, i.e. when being more physical active.
Example: Someone has a TDD of 50U insulin. 700/50 = 14. That means 14 grams of carbs covered by each unit of insulin. Again, theoretically.
MORE ACCURATE COUNTING
This method is the most used one in my home country, Sweden. Particular the method is used for children with autoimmune diabetes. Basically it´s based on calculating the amount of carbs and take a dose that gives an accepted glucose after meal and 2-3 hours later. It takes a while to find the individual insulin-to-carbs-ratio, ICR, and you should keep detailed written records when testing, also to find if any patterns in mornings etc. When using this method you can also, to some extent, adjust the timing of the bolus, fine tuning.
Example: I had 40 gram carbs for lunch, took 4U insulin and 3 hours later my glucose was 6 mmol/L (108 mg/dl). 1U covers 10 grams of carbs, so this ICR can be tried in other occasions eating something similar.
Compare meals, keep records and don´t focus at the carbs only. Use carb counting as a basis and remember, diabetes is not an exact science. There are several variables to contend with, so don’t hesitate to “throw out” results that are highly inconsistent with the rest of your data. Use your physician and endo team as much as you can. Remember that carb counting is theoretical and everything affect the glucose. You can learn a lot and find patterns that you get certain control over, but you can never win over diabetes. There are no shortcuts and you must remember, there may be a price putting too much efforts chasing a perfect glucose all the time. It´s not only a matter of physical well-being. Aim for a tie.
OVERKILL – NOT RECOMMENDED
Well, strange headline but there is a more advanced version of carb counting that is intriguing, even though very complicated. It is well established that not only carbs affect the glucose value and insulin need, also fat and protein have some impact. A number of studies have tried to find a more accurate way of including fat and protein when calculating the insulin dose (2, 3, 4). Most efforts in this area is made by Ewa Pańkowska, her bolus guide is referred to as “The Warsaw Method”. The method is based on using an insulin pump and uses both CU (carbohydrate units) as well as FPU (fat protein units), where insulin for the carbs is to be delivered immediately as a quick bolus and for fat and protein as a modified extended bolus. 1 FPU equals 100 kcal from protein and fat (kcal for protein and fat all together) and requires the same amount of insulin as 10 grams of carbs. The extended bolus depends on number of FPU. 3h for 1 FPU, 4h for 2 FPU etc. Studies shows great results but this method is very challenging and it´s extra important to consult your endo team before consider giving it a try.
100 RULE, 1800 RULE, CORRECTION DOSE OR ISF (INSULIN SENSIVITY FACTOR)
The 100 rule is used to calculate about how much how much insulin is needed to reduce glucose when having a hyperglycemia, high blood glucose. This is highly theoretic as well, and just gives a hint. Please be aware of that you might get a temporary insulin resistance if having a hyperglycaemia, which means you need more insulin than the factor shows. The 100 rule is calculated through divide 100 with your TDD (Total Daily Dose, including bolus and basal).
Example: You have a TDD of 50U. 100/50 = 2. That means 1U reduce blood glucose 2 mmol/L. The method is based on use of fast acting insulin such as Novorapid/Novolog, Humalog, FIAsp and Apidra. For other insulins, talk with your endo team.
If you measure glucose with mg/dl, the procedure is similar (5).
Example: You have a TDD of 50U. 1800/50 = 36. That means 1U reduce blood glucose 36 mg/dl.
References:
- https://www.niddk.nih.gov/health-information/diabetes/overview/diet-eating-physical-activity/carbohydrate-counting
- Systematic review; ”Impact of Fat, Protein, and Glycemic Index on Postprandial Glucose Control in Type 1 Diabetes: Implications for Intensive Diabetes Management in the Continuous Glucose Monitoring: http://care.diabetesjournals.org/content/38/6/1008.long
- http://journals.sagepub.com/doi/abs/10.1177/1932296816683409
- https://www.liebertpub.com/doi/10.1089/dia.2011.0083
- https://www.healthline.com/health/insulin-sensitivity-factor#calculating-the-factor
