If you’re into keto, you’ll probably already have an understanding of net carbs and fibre, however, there is some complexity to it that many nutritionists don’t even understand.
How to Calculate Net Carbs
30-June 2022, by Lee Sandwith
In this article, I will briefly explain some of the more complex aspects of net carbs in relation to fibre and calories.
Let’s kick off with a little reminder some basic info on carbs.
Simple and complex carbs
As you probably know, there are different types of carbs.
At the highest level, they are categorised into two broad group: simple carbs and complex carbs.
Both simple and complex carbs are broken down in the small intestine and later become used as a source of energy in the body.
Simple carbs are broken down (or metabolized) extremely quickly, whilst complex carbs are much more difficult to break down.
This is why you’ll often hear that the best carbs to consume, should you choose to do so, are complex carbs as they take longer to break down, and therefore keep you fuller for longer.
Essentially, both are still types of sugar, but complex carbs are longer molecules of the same stuff.
Whether you’re a carb lover or carb hater, this basic nutritional science cannot be ignored. It’s very basic metabolism.
Other types of carbs
There are two other types of carbs which are important in the context of keto: fibers and sugar alcohols, such as Erythritol, Monkfruit and Xylitol.
Fibre and sugar alcohols can’t be broken down as easily and our bodies don’t absorb them well to use them for energy.
These types of carbs don’t trigger an insulin response as glucose does not get into the bloodstream which would inhibit your body from getting into the state of ketosis.
It’s for these reasons that people following keto often disregard them from their daily carb count.
The basic concepts outlined above lay the foundations for the term net carbs.
Net carbs are the net (i.e. the difference) between the carbs that can be digested by the body and those which cannot.
Net carbs = total carbs – fibre - sugar alcohols
However, things get a little trickier when you dig deeper, in reference to fibre.
Net carbs = Total carbs – fibre – sugar alcohols
Different types of fibre
There are two types of fiber: soluble and insoluble fiber.
Insoluble fiber does not dissolve in water and can help speed the passage of bowel movements thereby preventing constipation. It contains no calories, nor does it spike blood glucose or insulin levels, and isn’t broken down by the gut
On the other hand, soluble fiber dissolves in water, and is digested by bacteria in the large intestine.
However, researchers have recently established that our bodies can actually derive a small number of calories from soluble fibre and that it can be absorbed by the intestine and used in the process of gluconeogenesis.
This means that fibre may slightly increase blood sugar and might have a small effect the process of ketosis.
How fibre is shown on nutritional labels
Because of the nuances between soluble and insoluble fiber, the way products are labelled, and the way calories are calculated, differ in different parts of the world.
Let’s start with calories.
The dictionary definition of a calorie is 'the energy needed to raise the temperature of 1 gram of water through 1 degree C'.
Typically, both carbs and fat as considered as deriving 4 kcal per 1g, and fat 9 kcal per 1g.
However, because fiber is more the most part indigestible, this also needs to be accounted for.
In the EU, this is dealt with by listing the fibre and carbohydrates separately on the label, and then calculating the calories by considering carbs as 4 kcal per 1g and fiber 2 kcal per 1g.
In the USA the fibre is [usually] listed as a sub-set of the total carbs and the calories counted by considering the total carbs as 4 kcal per 1g, not accounting for fibre by reducing the calories slightly as they do in the UK.
When I say “usually”, it seems that it is also acceptable to count calories using the EU method, so it gets a little complicated.
This poses two issues.
Firstly, the calories on any given product might be slightly different from country to country depending on which methodology they use.
And secondly, how you will calculate net carbs will also depend on from where your product originates.
If the product is from the EU, it’s easy as the ‘Total Carbs’ equates to net carbs so all of the work is done for you. If the product is from the US, you might have to deduct the fibre from the total carb count.
Take a look at the nutritional labels below.
You can see in this image how the labelling of fibre differs in the UK and USA. In the UK, the fibre is listed as a separate line item to carbohydrates. Therefore, the carbohydrates line is your net carbs.
In the first US label (the middle one), fibre is listed as a sub-set (indented line item) under the total carbohydrates. Therefore, your net carbs are 27g:
Net carbs = 30g total carbs – 3g fibre = 27g net carbs.
In the second US label, carbs are listed exactly the same as the UK version. Confusing hey? Don’t worry, there’s a simple way to think about it.
So what should you do?
I really wouldn’t worry so much about the difference in calories posed by fibre. We really are splitting hairs when trying to decide whether fibre derives 2 kcal or 4 kcal per gram.
Just accept that this isn’t an exact science and understand that your calories and net carb calculations will never be perfect, it’s always just an estimate.
It’s just good to know that this stuff gets quite complicated when you dig deep, but there are ways to keep it simple.
Start by focussing on net carbs rather than total carbs. If you feel that you’re struggling to get into ketosis, it might be an idea to start calculating total carbs.
If you use an app like carb manager, someone has probably already done the hard work for you, so you’ll only need to run any calculations on any weird and wonderful products that you come across.
If you’d like to understand this better, you can watch a video I recorded on this very subject, and if you’d like to discuss your nutrition with a professional, you can book a free 30-minute consultation with me.
About the author
Lee Sandwith holds a Masters Degree in Clinical Nutrition and is a registered nutritionist with the Association for Nutrition. You can book a free 30 minute consultation with Lee here.