Carbohydrate Counting 101

Carbs and Cals

Carbohydrate Counting is the method we now teach to allow those individuals on a basal bolus insulin regimen (a combined insulin therapy consisting of both background insulin and rapid acting insulin at meal times) to match their fast acting insulin to their dietary intake.

The premise is this method gives those on a basal bolus regimen (most likely those suffering with type 1 diabetes) more flexibility in their diet to eat whatever they want, whenever they want.

If you have had diabetes for many years, you may remember the days when you were given a set rapid acting insulin dose and told how many carbohydrates you can eat at meal times. This left patients diet very inflexible and little room for manoeuvre. If they did stray from their set carbohydrate doses, the blood glucose level would either spike above target levels or possibly induce hypoglycaemia. Therefore, carbohydrate counting allows more flexibility in your diet.

Carbohydrate counting essentially involves working out your carbohydrate intake at meals or snacks and then using a predefined ratio of insulin to carbohydrate to calculate how much rapid insulin you need to inject.

Lets get started

As the name implies, carbohydrate counting is concerned only with the foods which have a significant effect on your blood glucose levels, which are carbohydrates. Therefore, the first step is knowing which foods contain carbohydrate. I have produced another article on this previously that you can access by clicking here.

As a quick summary, carbohydrate containing foods can be split into 2 categories; starchy and sugar. Starchy carbohydrates consist of rice, pasta, potatoes, cereals, oats, any flour containing foods, batter and bread.

Sugar can be split into 2 sub-categories consisting of free/processed sugar or natural sugar.

Free sugars are sugars like cakes, biscuits, table sugar, sweets, sauces, full sugar pop drinks and honey, syrups and juices (these three are generally highly processed and/or act like free sugars once entering the body).

Natural sugars consist of fruit and milk sugars known as lactose. Therefore, any fruit needs to be considered for carbohydrate counting purposes and milk sugars, known as lactose, will also have an effect on your blood glucose levels with the exception of cheese whereby the lactose is processed out.

Calculating how much carbohydrate

Now you know what foods to look for, the second stage is calculating how many carbohydrates are in your meal.

Generally speaking, if the total amount at meals or as a snack is below 20g we would say this is insignificant and rarely requires rapid acting insulin. However, this is a general principle rather than a defined rule and some individuals may find they require some insulin with a small carbohydrate containing meal or snack.

There are several methods you can use in order to calculate the amount of carbohydrate in your meal. We’ll start with the most accurate method.

Food label reading

Every label containing food, by law, must provide you with the nutritional information per 100g. Some companies will help you out even further by providing the information per serving also.

Below is an example of a baking potatoes food label.

Typical Values 100g contains A typical 250g serving contains
Energy 345kJ (81kcal) 862kJ (203kcal)
Fat 0.1g 0.3g
Saturates <0.1g <0.1g
Carbohydrate 17.5g 43.8g
Sugars 0.8g 2.0g
Fibre 1.6g 4.0g
Protein 1.8g 4.5g
Salt <0.01g

Remember, for carbohydrate counting we are concerned with the total carbohydrate, not just sugars.

Lets pressure I was going to eat 180g of potatoes at my meal in this example. There are a few ways you can calculate the total carbohydrate content using the information provided per 100g.

The first and easiest way is to literally multiply by a percentage.

For example, I am having 180g of potatoes for my meal. I know there are 17.5g per 100g. I can therefore multiply 17.5 by 1.8 = 31.5g of carbohydrate in my meal.

Had I eaten 170g, I would multiple by 1.7,

160g multiply by 1.6,

140g multiply by 1.4

80g multiply by 0.8,

50g multiply by 0.5

40g multiply by 0.4

and so on.

The other way of doing of this is to divide the carbohydrate content by 100 and multiply by the weight of carbohydrate you are going to eat.

Carbohydrate content per 100g/100 X Weight of carbohydrate eaten.

Returning to the 180g example I would do the following:

17.5/100 X 180 = 31.5g.

Both get you the same answer. Personally I would use method one as it’s just a little bit quicker.


As you have probably guessed by now, in order to use the above example you will need to weigh carbohydrate containing foods prior to eating them. This isn’t as time consuming as it sounds and over time you will accumulate a working knowledge of the carbohydrate content for the typical foods and portions you eat.

Some patients even keep a crib sheet on their fridge with the values calculated for their staple foods. All they need to do is ensure you they are having the same portion at such meals.

If you cannot find the food label, all major supermarkets will have this information on their websites. All you need to do is log on and visit the grocery section of the site and search the food you want.

There are some shortcuts you can use when food label reading. For example, a slice of bread will be listed as one portion. You can then just add up the number of slices you have.

As the above potato food label demonstrates, the food label provides the nutritional information per portion, which equates to 250g. Therefore, if you find your portion works out as a quarter, half, three quarters or actually the same amount as the listed portion you can easily calculate the amount you are having. You may even weigh out your portions purposefully to match this method.

Carbs and Cals

This is a book and mobile application providing information on typical carbohydrate containing foods and lists various different portion sizes detailing the carbohydrate and calorie content of such foods. This allows the individual to eyeball the food on their plate and match it to the closest picture. This then provides you with the total carbohydrate for that meal.

Carbs and Cals Cabs and cals

Other applications

There is no shortage of other applications available on smart phones to help you estimate your carbohydrate content. Examples such as MyFitnessPal, Calorie Counter and MyPlate Calorie Tracker will all provide carbohydrate contents of foods once you have entered them in. However, for this to be accurate you will still need to know the portion you having.

Putting it into practice

We have now identified our carbohydrate containing foods, calculated the amount of carbohydrate in the food, now we need to know how much insulin to inject to match the carbohydrate.

This is the part where generic advice may not be suitable as it could compromise the patients safety. I will therefore outline the principle.

With carbohydrate counting we use a ratio of rapid acting insulin to the number of grams of carbohydrate.

For example, someone may use a ratio of 1:10g.

This would mean for every 10g of carbohydrate eaten, that individual needs 1 unit of rapid acting insulin.

Using this example, if I were to eat 60g of carbohydrate, I would need to take 6units of rapid acting insulin.

To find out your ratio you will need to contact your healthcare professional. A diabetes dietitian or diabetes specialist nurse should be able to give you a starting ratio or if you are newly diagnosed with type 1 diabetes you will be offered group education within the first year of diagnosis where your ratios and much more will be calculated.



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